Metal Corrosion and Zinc Wasting


On the long list of complex technical topics that boat owners face, corrosion of underwater metals is one of the most complicated, potentially most expensive and least well understood.  While it is not possible to ease the complexity or terminology of the topic, I can at least describe several related “stray current” metal corrosion phenomena in this one place.

Some readers may feel this topic is “beyond their pay grade.”  Like it or not, we all have a stake in understanding the basics.   At some time in boat ownership, most owners will face one or more corrosion issues.  Even for those for whom the topic is both uninteresting and obscure, all boaters should know how these phenomena are similar and how they are different.  Some familiarity will allow the affected owner to hire the right expert, understand remediation recommendations, and possibly avoid problems in the first place.

AC and DC “stray” electric currents flow in the water.  Because these currents flow outside their normal electrical conductors and devices, they are referred to as “stray currents.”  Worst case, all types of fault currents can be present at the same time.  Boaters should consider all electrical currents that flow in the water as a bad thing.


The basic concept in all corrosion is always the same: there is a voltage difference between two or more different metals, or alloys of metal, which are a) connected together electrically and b) immersed in an electrically active liquid.

The three major “stray currents” flowing in water (or in the earth’s crust) are:

  1. AC “ground fault” currents, resulting mostly from wiring errors aboard boats and occasionally from inadequate equipment design, incorrect equipment selection or AC appliance/equipment malfunction,
  2. DC “Galvanic” currents, resulting from the natural behavior of dissimilar metals in mineral-containing ground water, fresh surface water or sea water, and
  3. DC “Electrolysis” currents, a DC “ground fault” current, resulting from wiring errors, equipment faults, and improper equipment use.

While the basic electro-chemical processes and terminology of corrosion are always the same, the cause is context-specific.  Understanding the context (AC fault current, DC galvanic current, or DC Electrolysis current) is essential to avoiding confusion caused by the shared terminology.

“Electrolysis,” or “Electrolytic corrosion,” is  frequently confused with, but very different from, “Galvanic corrosion.”  To repeat, the concepts and terminology are shared and common to both phenomena; it is the “cause and origin” of the driving voltage that is different.  

No matter the terminology, corrosion currents are a silent attack on every boat, and can cost many hundreds or thousands of dollars for those who don’t mount an appropriate and effective defense.


AC fault currents flowing in the water are often dangerous to people, pets and wildlife.

Worst case, AC fault currents can lead to death by “Electric Shock Drowning:” (ref:  Children and pets must never swim in a marina’s basin.  Boat owners and professional divers performing in-water maintenance on boats must be alert to the causes and consequences of AC electric currents in the water.

In general, AC fault currents DO NOT deteriorate the underwater metals of boats and do not cause rapid zinc wasting.   There is a great deal of technical understanding about environmental AC ground fault currents that comes from the utility and transportation industries (power transmission, buried utilities, pipeline and railroad).   The 60 Hz AC power found across North America changes polarity 120 times per second.   Whatever molecular metal material that might be removed from a metal in one half-cycle is re-deposited in the second-half cycle.  (Cit: “DC Currents in the Bilge – Not AC – Is the Culprit When Metal Fittings Corrode,” Robert Loeser, Seaworthy Magazine, October, 1996).   AC fault currents must be very large before metal corrosion results.   The AC voltages found around pleasure craft docks (less than 600V) DO NOT cause zinc wasting.

Aluminum can be an exception.  Aluminum can be damaged by AC stray currents IF the density of the fault current is greater than 40 Amps per square meter of aluminum surface area (40A/M2).  What that means in English is: a relatively high AC fault current in the water will cause erosion to a relatively small chunk of underwater aluminum.  This combination would be unusual, but not impossible, in pleasure craft marinas.  One m2 is equal to about 10.75 ft2, so it would only take 3.7 amps of AC stray current to cause corrosion damage to a 1 ft2 aluminum part.  This is not an extraordinary leakage current, but 1 ft2 is a small piece of aluminum.  So trim tabs and outdrives may be “relatively” “safe” at levels that would waste aluminum anodes installed for galvanic protection.  On boats without other aluminum parts, aluminum anodes can waste quite rapidly in proportion to the size of a moderate in-water AC fault current.

Readers can find information on testing for AC ground and leakage fault currents in layman’s language on this website, here:   The reference article helps owners bring their boat into compatibility with National Electric Code (NEC) standards that require ground fault sensors on docks, and it also dovetails well with identifying and eliminating corrosion issues.

Be aware that some in-water AC stray currents can originate from sources on land.  In that case, the fault current will flow on the green AC safety ground wire (a component of the boat’s bonding system), originating in the basin water and flowing back into the shore power infrastructure.  This situation is not caused by a problem on the boat, and in general, is not something a boat owner can fix.  Always report this finding to marina management.


  1. Assess the boat for AC ground fault and leakage fault conditions.  (ref:
  2. Correct all issues in order to establish a defect-free starting-point baseline.
  3. Consider installing Equipment Leakage Current Interrupter (ELCI) sensors on boat shore power AC service circuits.  (ref: ABYC E-11, 11.11.1 and
  4. Where automatic ELCI sensors are not installed, perform frequent manual monitoring of AC shore power cords with a decent-quality clamp-on Ammeter.  (ref:
  5. Correct any newly discovered issues as soon as they present themselves.


  1. DC galvanic currents are associated with small voltage potentials that are a naturally-occurring characteristic of all metals.  The specific voltage is determined by the atomic structure of the individual metal (or metal alloy).
  2. Different metals have different naturally-occurring electro-potentials.
  3. A “Galvanic Series” is a list of metals sorted by their naturally-occurring characteristic electro-potentials.  Different “references” can be used for ordering a “galvanic series.”  The best reference for salt water is a silver/silver chloride cell.
  4. A “galvanic couple” is any combination of two or more dissimilar metals or metal alloys connected together electrically and immersed in an electrolyte.
  5. An “electrolyte” is an electrically conductive liquid (generally) medium.
  6. Dry Corrosion” is the direct attack on a metal by dry gasses (air, oxygen) through chemical reactions which result in surface oxidation.
  7. Wet Corrosion” is the direct attack on a metal by an aqueous solution (strong or dilute, acidic or alkaline) through electro-chemical reaction.  Moisture and oxygen can act by themselves.


The underwater metal alloys on a boat together with the minerals in the surface water in which the boat is floating create the elements of a “galvanic cell” (a battery).  Galvanic currents will always be generated when a boat with dis-similar metals occupies water containing dissolved minerals.  A zinc/copper galvanic couple (common “dry cell” flashlight battery) is a “galvanic cell.”  A “lead/acid” automotive or boat battery (wet cells, AGM or Gel) are examples of “galvanic cells.”

When the metals making up the galvanic cell (battery) are actually the underwater component parts of a boat (bronze, aluminum, stainless steel), the naturally-occurring galvanic currents result in corrosion of some of the underwater metal.   The mineral concentration of sodium, calcium and magnesium salts and many others in the surface water affect the speed at which galvanic corrosion proceeds.

The flow of electrons in a DC galvanic current is always from a more active metal (anode) to a less active metal (cathode) on a Galvanic Series.   All environmental surface water, whether fresh or salt, acts as an electrolyte.  Salt water carries more mineral ions than fresh water, so is more “efficient.”

Galvanic corrosion is a slow process that occurs over many months.  Since it’s the anode in a galvanic cell that dissolves, the point of avoidance/remediation is to artificially force the metal(s) to be protected relatively more cathodic compared to a sacrificial metal present in the electrolyte (water).  This is done by adding a “sacrificial anode” made of a very active metal (aluminum, magnesium, zinc) to the mix of less active but more valuable underwater metals on a boat.

Perhaps a ”before” and ”after” view:


Figure 1 shows a ”before view” of a galvanic couple lying in seawater.  The stainless steel (SS) is the anodic alloy, so it erodes due to the natural galvanic voltage between it and it’s cathodic bronze couple-mate.


Figure 2 shows an ”after view” of the same galvanic couple with the addition of a sacrificial zinc anode.  The zinc forces the SS relatively  more cathodic (relative to the zinc), so the SS part is now protected from corrosion.  The zinc is the most active (anodic) metal in this new couple.  By corroding, the zinc acts to protect all of the more “valuable” metals.

Ongoing zinc maintenance is required to provide continuing protection of the more important components of the couple.  Additional valuable corrosion control techniques include the installation of galvanic isolation devices in shore power ground conductors, cable TV coax ground sheathes, and the ground conductors of (now pretty much obsolete) wired telephone and wired Ethernet connections.


The propulsion and genset drive engines on most cruising-sized pleasure craft are fit with two-stage engine cooling systems.  In diesel cooling systems, a coolant (“fresh water”) circulates through the engine block, heads, oil-cooler, turbo-charger, and intercooler.  A heat exchanger transfers waste heat from the fresh water coolant to environmental raw water, where it is eliminated via the raw water exhaust.  Commonly, a second heat exchanger transfers waste heat from transmission fluid into exhausted raw water.

Electro-chemically, the raw water passing through the heat exchanger is an electrolyte.   Heat exchangers contain several different alloys of copper and nickel.  The alloys used in heat exchangers are designed to have galvanic voltage potentials that are close to one another on the salt-water galvanic series.  That greatly slows, but does not stop, the galvanic corrosion which occurs within heat exchangers.  The dissimilar metals of the heat exchanger act as the galvanic couple and the raw water is the electrolyte.

If galvanic corrosion in heat exchangers is allowed to continue uninterrupted, pinpoint leaks will develop in the shell or tubes of the exchanger.  Similarly, pinpoint leaks can develop in raw-water cooled oil coolers, transmission coolers and intercoolers.   The result over time is damage to expensive heat exchangers, as well as the possibility of secondary damage to the engine itself.   Boat owners  must be aware that there are zincs located within the raw water channels in engines and heat exchangers.

Boats with wood, steel and aluminum hulls require special anti-corrosion techniques.  Many sacrificial anodes are required to protect the surface area of metal hulls.  Too many anodes can cause paint to peel from a metal hull, and cause damage to the woods of a wooden hull.  Alternatively, systems such as Electro-Guard ( apply a voltage to a metal hull.   These “Impressed Current Cathodic Protection” (ICCP) systems protect the hull plates and welded joints from galvanic attack by making the hull cathodic to its surrounding environment.   This is one of many areas that are “different” for owners of metal-hulled boats vs hulls of fiberglass reinforced plastic (FRP).


SS, bronze, brass and galvanized steel are metallic alloys that contain several elemental  metals within their compounding mix.   Dissimilar metals within the alloy can experience galvanic corrosion.  “Single metal” corrosion results in micro-fractures in the material’s structure, and often results in surface pitting.  The process can proceed to structural failure.

Anodic and cathodic areas form on the surface of alloys due to surface imperfections in the alloy mix, lack of oxygen and/or other environmental factors.  The anodic areas in the matrix give up electron(s).  The ions left behind form into the visible hydroxyl oxidation residue that is shed.  Corrosion currents flow at the expense of the anodic metal of the circuit, which corrodes continuously.

SS shaft logs and propeller shafts, SS rudders and rudder posts, SS fasteners that attach swim platform brackets to an FRP hull, SS keel bolts, SS exhaust port fasteners, etc, etc, are all candidates for a form of single metal galvanic corrosion called “crevice corrosion.”

In brass that contains more than 15% zinc, like the manganese bronze alloy often used in propellors,  unprotected fittings can undergo a single metal galvanic corrosion process called “dezincafication.”  Zinc within the brass alloy erodes away, leaving behind a weak matrix of copper and small percentages of other metals (such as nickel, chromium, manganese) of the original casting.  What’s left is structurally weak and can fail catastrophically.  “Dezincification” leaves a characteristic “pinkish” color to what once had a golden bronze color; particularly so in broken, exposed areas of a part.

In stainless steel, this process is called “CREVICE CORROSION.”  In aluminum, the analogous process is called “POULTICE CORROSION.”  When stale water lies against stainless steel for long periods or time, the water looses it’s content of dissolved oxygen.  Oxygen-depleted water in prolonged contact with stainless steel promotes crevice corrosion, leading to possible structural failure in stainless steel parts and fittings.  Similarly, water that lies in contact with aluminum for long periods of time promotes poultice corrosion.  Poultice corrosion can result in pinpoint leaks in aluminum fuel tanks.

For thruhulls especially, boaters should use fittings of bronze or Marelon; BRASS FITTINGS SHOULD NEVER BE USED UNDERWATER.

For those interested, I have more details on Galvanic Corrosion and the Galvanic Series for salt water on this website, here:

BoatUS has a good article on electrochemical corrosion on their website, here:

David Pascoe has a good article on electro-chemical corrosion on his website, here:


  1. Install a complete bonding system if one is not currently present.
  2. Install zincs to protect bonded underwater metals.
  3. Perform routine maintenance of zincs on underwater metals: propellor shaft, rudder, and other underwater metal structures.
  4. Maintain the “master” zinc that protects the boat’s bonding system.
  5. Maintain zincs protecting engine and transmission cooling system components.
  6. Use deck fill screw-on covers that are galvanically compatible with under-deck fittings to avoid galvanic corrosion and hidden fuel leaks.
  7. Install an appropriately rated Galvanic Isolator in the shore power safety ground if one is not already present.
  8. Install galvanic isolators to telephone, Ethernet and TV Cable feeds that come onto a boat from shore.


The source of the voltage that drives the process is what distinguishes a “Galvanic current” from “Electrolysis,” or an “Electrolytic” current.  Recall that galvanic voltages are a function of the natural atomic electro-potential of the metals of a galvanic couple.  The voltages which cause electrolysis are man-made, not naturally-occurring.  The voltages that drive electrolytic corrosion are often significantly larger than galvanic voltages, and the destructive impact of a DC fault causing electrolytic damage is much faster and more aggressive than galvanic currents.

In Figure 3, the metallic actors (SS and bronze alloys) are the same as shown in Figure 1.  In this case, the elemental voltage polarity of the couple has been reversed by the application of an outside source of DC voltage.  This is a DC fault scenario.  The bronze thruhull in this example will disintegrate, freely giving up it’s copper content into the surrounding sea water.


Figure 3: A DC Fault Injecting Power to the Bonding Buss Resulting in Corrosion of Important Underwater Metal Alloys

Electrolysis voltages originate with an externally- supplied DC source; i.e., a battery or its equivalent.  Causes can be a wiring error, chafed/frayed DC conductor, defect or age-deteriorated insulation on a bilge pump B+ wire lying in bilge water, a defect in a DC power supply or a DC generator, a failed piece of DC equipment or misapplication of use of DC equipment.   A common wiring error that can lead to electrolysis currents results from incorrectly wiring the neutral return circuit of a DC device to the boat’s bonding system.  NEVER USE THE DC BONDING SYSTEM FOR THE ELECTRICAL RETURN PATH FOR DC CIRCUITS.

DC electrolysis currents are equivalent to the industrial process called “electroplating.”   In a marina, failed DC equipment can deliver a DC voltage into the basin water.  On a boat, wiring error or a failed piece of equipment can apply a DC fault voltage to the boat’s ground buss.  Electrolysis current flows IN ONE DIRECTION through the ground path and into the surrounding basin water.  The anode literally dissolves.  The fault can be on the same boat as the failed equipment, on a neighboring boat or in nearby land based equipment.  Or it can be, simply, in between a source point and a return point.  The fault can be located in shore-side infrastructure wiring, or it can be because of misuse of equipment by a contractor, such as a welder or a DC motor on a marine railway or travel lift.

It is a law of physics that electric current always seeks the path of least-resistance back to their source.  Scenario: imagine three adjacent slips on a dock.  In slip #1 is a boat with a fault and dumping a DC electrolysis current into the basin water.  Slip #2 is empty.  In slip #3 is a boat providing a path to ground for the fault current via it’s shore power cord.  So far, only boat #1, the boat with the fault, has a corrosion problem.

Now a transient boat comes into slip #2.  The fault current previously passed through slip #2 on the way to ground, but when the transient arrived, that boat’s protective electrical system (Bonding System) becomes inserted into the path of the fault current.  The transient’s bonding system has a lower resistance than the surrounding basin water.  The fault current passes into the transient via one or more underwater metals, passes on through the transient’s bonding system, and exits back into the basin “on the other side” of the transient.  The fitting(s) where the current exits the transient will corrode.  That fault current is now causing damage to boat #1 and boat #2.  Boat #2 is a true victim, safe if plugged into shore power, potentially damaged if not.

All fault currents are always opportunistic.  They simply follow the rules of physics to find the “path of least resistance” back home.

The rate at which metal loss occurs is proportional to the voltage involved and to the many Ohms Law factors that determine the magnitude of accompanying current flow.  At its worst case, this process can sink a boat astonishingly quickly (a matter of hours/days), because with large uni-directional electrolytic currents (electroplating), metal mass can erode away from the anodic terminal(s) very quickly.   The part that gives up metal mass will ultimately suffer structural failure if the process is not interrupted.  If it happens to a thruhull on a boat in the water, the boat will sink.   All underwater metals – propellors, rudders, struts, trim tabs and radio ground planes – can be effectively “dissolved” by these stray electrolysis currents.

The best articles I know of for an understanding of this topic are by Capt. David Rifkin, who has good reference articles on his website, here:

Nigel Calder, Ed Sherman of ABYC and Steve d’Antonio have also written about these phenomena,  mostly in fee-based subscription publications like Professional Boatbuilder and Passagmaker Magazine, or in their own for-fee publications.


Like all metal corrosion, zinc wasting is a form of electro-chemical corrosion, always due to DC currents.  Electrical measurements of the basin occupied by the boat would be necessary to determine which mix of stray currents are present at any given time, but zinc wasting is a DC phenomena, and by far most commonly, a galvanic phenomena.

Boat owners can do their own basin-water testing, but it is not a process I would recommend for the electrical layman.   An understanding of the theory of these types of faults, understanding the probes and tools that are necessary, and the skills to correctly interpret test results are necessary.  This can be quite confounding, even to experts.

Boat owners that experience corrosion issues would be better served to hire an ABYC CORROSION-CERTIFIED MARINE ELECTRICIAN.  That said, skilled and knowledgeable boat owners can do their own DC testing with a silver/silver chloride half-cell.  High quality Digital Voltmeters (DVM) can detect AC ground fault currents, DC galvanic currents and electrolysis currents, but detection and evaluation is highly specific and sensitive to the placement of the measurement electrodes, quality of the test equipment, and conductivity of the surrounding basin water.

By the time a layman has bought the tools, learned to use them, and learned to interpret the results, said layman would be better off financially in hiring a professional who could provide the diagnosis and remediation recommendations as a one-time service.


  1. Diligently avoid having DC wiring wetted or submerged in bilge water.
  2. Never use the boat’s bonding system as a B- “neutral” return circuit for DC attachments.
  3. Avoid facilities (marinas, municipal or private docks, boatyards, etc) where the infrastructure appears to be poorly maintained.
  4. Be alert in marinas located in industrial neighborhoods where ground fault currents from shore sources may be more likely; check with the dockmaster for known issues in the basin.
  5. Avoid facilities with numerous boats that are in a poor state of maintenance and repair.



Oxidation occurs with the release of electrons and the simultaneous shedding of positively charged metal atoms which detach from the surface of the metal.  These particles enter the electrolyte solution as positively charged ions.  Chemically:

Fe → Fe++ + 2e (example with Iron);

Zn → Zn++ + 2e (example with Zinc);

Pb → Pb++ + 2e (example with lead).


Free electrons reach the cathode and react with hydrogen ions in the electrolyte.  Hydrogen bubbles will often form on the cathode; clearly visible in lead/acid batteries.  Chemically:

2H+ + 2e → 2H


If acid is not available, water itself will break down (dissociate) to generate hydrogen ions (H+).  The specific chemistry here depends on the composition of the electrolyte.  Assuming water, water dissociates, forming free hydrogen and hydroxyl ions:

H2O ⇌ H+ + OH

Then, metal ions combine to form metallic oxide, which is the corrosion product:

Fe++ + 2(OH) → Fe(OH)2, or

Zn++ + 2(OH) → Zn(OH)2, or

Pb++ + 2(OH) → Pb(OH)2

Electrical System Topology

Electrical System Schema:

The schema of Sanctuary’s vessel-wide electrical system contains three major divisions.  This diagram is specific to Sanctuary, showing two 30A shore power connections and a fully-integrated but modestly sized inverter/charger.  That said, the overall model generalizes very well to larger electrical systems based on voltage, inlet, inverter/charger and load capacities and configurations.

  1. AC electrical system division of the vessel includes:
      • 120V Shore Power inlet connections
      • AC Generator (Genset)
      • ABYC-compliant Generator Transfer Switch
      • AC Branch Circuit Distribution Panel(s) – (NewMar – House loads; Weems & Plathe – heat pumps, raw water circulator)
      • Galvanic Isolator
  2. DC electrical system division of the vessel includes:
      • Battery Bank
      • Propulsion engine alternator
      • DC Branch Circuit Distribution Panel(s)
      • Individual component attachments (Thrusters, Windlass, Autopilot, Entertainment, Inverter/charger, etc.)
  3. Interface, or Bridging, or Power Conversion division of the vessel includes:
      • Magnum MS2012 Pure Sine Wave Inverter/Charger

General Topology of the Vessel Electrical System:


An Adobe Portable Document Facility (.pdf) version of this drawing is available by clicking this link: 20161019_electrical_system_topology.

AC Electrical System

AC System Overview:

Note: An electrical diagram of Sanctuary’s AC Power Distribution  System as described in this article is located here (Adobe Portable Document Facility (.pdf) file): 20161022_ac_electrical_distribution_system.

The ship is wired to operate from two single-phase, grounded-neutral, 120VAC, 30A shore circuits originating in a dockside shore power system.  Neither the shore grounded (white) neutral conductor (white) nor the ungrounded energized conductor (black) is connected to the safety ground (green) aboard the ship (ABYC E11,

The ship’s AC safety ground (green) and DC negative buss (black) are connected together in the engine room (ABYC E11, and subs).

The ship is fit with a ProMariner® Prosafe-1™ galvanic isolator.  AT the time of it’s installation, the device complied with the then requirements of ABYC A28, 28.13 (now obsolete). The diode pack of the device is installed in series with the ship’s incoming green safety ground wire. The isolator and its control module are located in the ship’s electrical closet. The enumerator/monitor is mounted at the ship’s electrical control center located stbd, in the companionway to the vee berth.

Note: the ProMariner® galvanic isolator control module was disconnected in May, 2016.  The design of the enumerator/control module places a ground fault on the incoming shore power circuit.  That ground fault is used by the device to test the ship’s safety ground wire for continuity.  That ground fault can trip shore power ground fault sensors.  Disconnecting the enumerator does not affect the purpose or operation of the diode pack itself, but it does defeat the self-checking feature of the OEM design of the enumerator/monitor.

The ship is fit with two 120VAC, 30 Amp SmartPlug® marine shore power inlet connections (ABYC E11, and subs). “Shore 1” corresponds to a Newmar® ACDC-1™ “house” AC Load Center (identified with the numeral “1”). AC branch circuit breakers (ABYC E11, and subs) serving the genset battery charger, refrigerator/freezer, 120VAC water heater, inverter/charger and several house utility outlet circuits are installed. “Shore 2” corresponds to a Weems and Plath® “heat pump” Load Center (identified with the numeral “2”). AC branch circuit breakers (ABYC E11, and subs) serving two reverse cycle heat pumps and a raw water circulator pump (“air conditioner” units) are installed.  It is not necessary to connect both shore power circuits in order to use either one; each is completely independent of the other.

The ”AC Master Breaker” on the NewMar® “house” AC Load Center and the ”Master Breaker” on the Weems and Plath® “heat pump” Load Center function as shore power disconnect switches (ABYC E11, and subs and 1). These double-pole breakers isolate their respective AC shore power circuits from the ship’s on-board AC distribution system. The 120V energized current-carrying (“hot”) buss on the AC side of the NewMar® Load Center has been modified from its OEM configuration. Breakers 1-4 on the NewMar® panel are fed by shore line-in or generator power. Breakers 5-8 on the NewMar® panel are fed by the onboard inverter/charger as described later in this document.


  1. NoteThis section of E11 was upgraded to include ELCI in the July, 2012 release of the standard. Sanctuary complies with the July, 2009, release, E11, Sanctuary is not fit with ELCI at this time.

The ship is fit with an ONAN® MDJE™ onboard generator. The generator is powered by aa Onan 2-cylinder, 4-cycle diesel engine. Diesel fuel for the generator engine is drawn from the ship’s onboard fuel tanks. The generator has a 2-stage (fresh water with heat exchanger) cooling system. The generator is rated for continuous operation at 7.5kW, 60Hz. Generator operation (glow plugs, start/stop) is controlled by two rocker switches mounted at the ship’s electrical control center.  The generator and its diesel engine are mechanical devices that require periodic preventive maintenance. Refer to the Onan manual for maintenance schedules.  The generator’s AC output is wired in a 240VAC configuration. The generator starter motor is fed through a BlueSea Systems ML-RBS remotely operated DC disconnect switch (ABYC E11,,

The ship is fit with a Blue Systems® p/n 9093 manual Generator Transfer Switch. The GTS transfers the ship’s AC distribution load centers to either the shore power inlets or the onboard generator. When shore power is available, and the load center disconnect switches are set “on,” the corresponding green “Shore Power” LED on the GTS operator’s panel becomes illuminated. The GTS is of the break-before-make design. This prevents simultaneous cross-connection of incoming shore power source(s) and the ship’s generator (ABYC E11, This allows the generator to be started and run for servicing while the ship is simultaneously connected to energized (live) shore power connections.

Shown following is the wiring layout of the GTS as installed. Shore power service cords feed “Source 1” and “Source 2.” The 240V onboard Generator feeds “Source 3.” The NewMar® AC Load Center for “house” loads is connected as “Load 1;” the Weems & Plath® Load Center for  heat pumps is connected as “Load 2.” The GTS is shown in the “Shore” position. If the generator is “running,” the green “Generator” LED on the GTS operator’s panel becomes illuminated. If both shore and generator power are available at the same time, both sets of LEDs will be illuminated.


The ship is fit with a Magnum® MS2012™ Pure Sine Wave Inverter/Charger.

  1. When either shore or generator power is available, the device operates in “Passthru” mode to forward AC power to utility outlets via circuit breakers 5–8 on the NewMar® AC Load Center and to simultaneously charge the ship’s battery bank. When shore or generator power is not available, the device operates in “Invert” mode as the AC power source for circuits 5-8. The device automatically switches between its “passthru” and “invert” modes as availability of shore or generator power changes.
  2. The neutral buss for branch circuits powered by the inverter/charger is isolated from the neutral buss for branch circuits powered solely by shore or generator power. Magnum requires this separation, which they base on ABYC A31, However, AC neutrals are defined to be “grounded conductors.” Therefore, this ABYC reference seems obscure, since it refers to separation of “ungrounded conductors.”
  3. Configuration of the operational status of the inverter/charger is manually selectable via the ME-RCtm Remote Control mounted at the ship’s electrical control center area.
  4. The “fault” lamp on the ME-RCtm Remote Control indicates a problem that prevents normal operation of the inverter/charger. The two most common faults are spike voltages and out-of-tolerance frequency deviations. These faults sometimes occur when the ship is operating on the generator as its AC power source and heavy loads cycle “on” and “off.” These “faults” can be manually cleared by recycling DC power via the inverter/charger battery disconnect switch in the engine room space.
  5. DC electrical energy to power the inverter/charger originates from either 1) the propulsion engine’s alternator (supplemented by the battery bank), if the ship’s propulsion engine is running, or 2) solely by the ship’s battery bank, if the ship’s propulsion engine is not running. In the absence of shore or generator power, the DC ampere-hour (aHr) capacity of the ship’s battery bank can be conserved by discontinuing use of the Inverter/Charger and its attached AC loads.

Finally, the ship is fit with a 700-watt Xantrex® Modified Sine Wave (MSW) utility Inverter. This inverter is an alternative AC power source that can feed a utility outlet power strip on the ship’s salon nav station. This inverter is a stand-alone device that is not integrated into the ship’s AC distribution system. It is available to power the satellite TV receiver/DVR and the TV. DC energy supply for this inverter is as described above. The device mounted on the aft bulkhead of the ship’s standing closet.

DEFINITION: “Secured State” of the Ship’s AC Electrical System

Aboard Sanctuary, a “secured state” for the AC Electrical System is defined to exist when all of the following conditions exist:

  1. All individual AC house circuit breakers on the NewMar® AC Load Center are in the “off” position,
  2. All individual heat pump circuit breakers on the Weems & Plath® Load Center are in the “off” position,
  3. The “AC Master Breaker” on the Newmar® AC Load Center and the “Master Breaker” on the Weems and Plath® Load Center are both in the “off” position,
  4. The generator transfer switch is in the “off” position,
  5. Shore power service cords are disconnected and stored aboard,
  6. The generator is not running,
  7. DC power to the Xantrex® MSW Inverter is discontinued via it’s disconnect breaker, located in the electrical closet,
  8. DC power to the Magnum® MS2012tm system-integrated Inverter/Charger is discontinue via the DC rotary disconnect switch located in the engine room, stbd bulkhead.

References to ABYC E11 contained in this document:

All references to ABYC E11, AC AND DC ELECTRICAL SYSTEMS ON BOATS, are to the July, 2012, release of the standard unless otherwise noted.

DC Electrical System

DC System Overview:

Note: An electrical diagram of Sanctuary’s DC System as described in this article is located here (Adobe Portable Document Facility (.pdf) file): 20161022_dc_electrical_distribution_system.

The ship’s DC electrical system is a “negative ground” system. (ABYC E11, 11.4.24 and

The DC system is of the “ungrounded” system design (ABYC E11, 11.4 and E11,

The ship’s AC safety ground (green) is bonded to the Ship’s DC negative buss (black) in the engine room. (ABYC E11,

DC energy for the “house” and “engine start” services originates in a single battery bank comprised of six, 6 volt, flooded deep cycle “Golf Cart” batteries. Over-current protection (OCP) for the battery bank is provided by BlueSea Systems®, Type MRBF™, 200A fuses. (ABYC E11, and and subs).  Details of that design decision are discussed in my article, “Battery Bank: Separate vs Combined,” on this site.

A single Group 27 start-service battery is used to start the ship’s generator. A BlueSea Systems® model ML-RBS™ remotely operated disconnect switch, with p/n 2145 remote switch, is fit in the generator’s battery feed circuit.

The ship’s Main DC Disconnect Switch (ABYC E11, and subs) for the DC feed to the NewMar® Load Center and other attached DC loads is located in the engine room, stbd bulkhead, above the ship’s battery bank.

The ship’s OEM NewMar® Model ACDC-1™ Branch Circuit Load Center/Distribution Panel is located to stbd in the forward companionway to the vee berth. Because there is a combined battery bank for house and start functions, the OEM Battery Selector Switch is discontinued and removed. The left half of the Newmar® Load Center serves as the DC Load Attachment Center for many DC attachments, including:

  • navigation, anchor lights and deck lights,
  • LPG safety shutoff valve,
  • refrigerator/freezer DC feed,
  • house drinking water pump,
  • raw water wash-down pump,
  • DC lighting,
  • salon VHF radio,
  • windshield wipers and horn,
  • toilet macerator, and
  • stereo.

This panel provides over-current protection for attached loads via circuit breakers. (ABYC E11,

The ship is fit with a Blue Sea® System WeatherDeck™ DC Circuit Distribution Panel, located stbd on the flybridge. It is the primary load attachment center for the ship’s navigation instruments, including:

  • chart plotters (including Radar),
  • auto pilot controller,
  • VHF radio,
  • depth sounder,
  • under-console AIS receiver and wi-fi multiplexor, and
  • flybridge DC utility outlets.

This panel provides over-current protection for attached loads via circuit breakers. (ABYC E11,

The ship is fit with a Magnum® MS2012™, Pure Sine Wave (PSW) Inverter/Charger. DC over-current protection is provided by a 300A Class “T” fuse (ABYC A31, and subs; The DC Disconnect Switch for the inverter/charger is located in the engine room, stbd bulkhead, above the ship’s battery bank. (ABYC E11, and subs)

DC Power for some ship equipment attaches to the vessel’s DC Distribution System independently of the NewMar® load center. These attachments have individual over-current protection. These attachments include:


Location of Attachment’s
Disconnect Switch
or OCP

(ABYC E11, and subs, 11.10 and subs)

1 propulsion engine
a) starter motor feed and
b) control, instrumentation and instrument lighting circuits
fwd surface of galley drawer cabinet, floor level, aft of stbd salon door; switch is accessible without opening the engine room. This circuit is without OCP. (ABYC E11,, Exception 1)
2 Lewmar® H900 windlass tagged; on vessel’s electrical control center
3 Dickson® stern thruster Inline fuses, respective operator’s panel
4 Garmin® GHP10tm autopilot system tagged; engine room, stbd, mid-ships, above battery boxes
5 Magnum® MS2012tm, 2kW, PSW inverter/charger tagged; engine room, stbd, mid-ships, above battery boxes
6 ICOM® 706MKIIGtm Amateur Radio Transceiver Inline fuses, electrical closet, NewMar® B+ buss
7 bilge pump tagged; electrical closet aft bulkhead, eye level (tubular glass fuse)
8 high bilge alarm tagged; electrical closet aft bulkhead, eye level (tubular glass fuse)
9 shower sump pump tagged; electrical closet aft bulkhead, eye level (tubular glass fuse)
10 SirenMarine® Spritetm Boat Monitor inline fuse, electrical closet
11 salon +12VDC utility outlet. inline fuse, electrical closet

Battery State-of-Charge Status & Monitoring:

The ship is fit with six, Duracelltm, EGC-2, Golf Cart batteries.  These batteries have a 20-hour Ampere Hour (aHr) rating of 230 aHr and a Reserve Capacity rating of 448 minutes. These batteries are manufactured by East Penn Manufacturing® and are sourced from Sam’s Club. The batteries are combined in a series/parallel configuration to provide 12VDC.

The overall total rated ampere hour capacity of the ship’s battery bank is 690 aHr.

A Magnum® ME-RCtm Remote Control, and a Magnum® ME-BMKtm Battery Monitor Kit, are installed to monitor the ship’s DC electrical operating parameters and the state-of-charge status of the ship’s battery bank.

“Standard operating practice” aboard ship is to adhere to the “mid-capacity rule,” which states that lead-acid batteries (flooded wet cells, AGM or Gel) should not be discharged beyond 50% of their rated capacity and that discharging a lead-acid battery in excess of 50% of its capacity shortens its service life. Aboard ship, the ME-RCtm/ME-BMKtm Battery Monitor displays the “State-of-Charge” of the battery bank. Less overall depth-of-discharge is better.

The approximate eight-hour overnight (summer hours-of-daylight) DC system electrical consumption (refrigeration, anchor lighting, evening TV watching, computer use, etc.) aboard ship is 125 – 150 aHr. The approximate eleven-hour overnight (winter hours-of-daylight) DC electrical consumption is 150 – 200 aHr.

Battery Charging:

Shore Power/Onboard Generator:
When the ship is receiving AC power from either 1) shore power or 2) from the ship’s onboard generator, the ship’s battery bank is charged by the Magnum® MS2012tm 2kW Inverter/Charger 1.

Under way:
The ship’s engine alternator charging system consists of a single, 12-volt, 110 amp, Balmar® high-output alternator, model 712110, with a Balmar® MC-614tm external regulator. The external regulator receives its DC input power supply from the propulsion engine’s starter solenoid 2.

DC Distribution Wiring: 3

  1. Three attachments originate at the positive battery post of the ship’s battery bank:
    1. Attachment 1 is BlueSea Systems®, Type MRBFtm Fuse Block, p/n 2151, fit to the designated positive output terminal. (ABYC E-11, This fuse block is fit with two, 200A, Type MRBF fuses.
      • Fuse 1 feeds the ship’s Main DC Power Disconnect Switch 4, a Blue Sea® Systems, p/n 6006, rotary switch, via a 2-0 AWG red wire. A 2-0 red wire continues from the disconnect switch to a BlueSea® Systems, 150A, Type ANL fuse block. The house DC feed is a 2-0 AWG red wire from the ANL fuse block to a 600 amp, 4-post terminal block. The terminal block is the ship’s Main DC Power Distribution Buss.
      • Fuse 2 connects the ship’s Balmar 110A alternator to the battery bank, via a #6 AWG red wire.
    2. Attachment 2 is a 2-0 AWG red wire that feeds the ship’s propulsion engine starter solenoid through a BlueSea System®, p/n 6006, disconnect switch located in the salon, stbd, beneath the fold-down table. This circuit is not overload protected (ref: ABYC E-11,
      • The propulsion engine starter solenoid is the DC system attachment point of the engine’s DC sensors, controls, instrumentation and malfunction alarms, and the external Balmar® MC-614tm voltage regulator which energizes the on-engine Balmar® alternator unit.
    3. Attachment 3 is a 2-0 AWG red wire (ABYC, E-11, that feeds the ship’s inverter/charger through a Class “T” fuse block fit with a 300 Amp, Class “T” fuse. A 2-0 AWG red wire continues from the Class “T” fuse block to a BlueSea Systems® p/n 6003e disconnect switch. From the disconnect switch, a 2-0 AWG red wire feeds the Inverter/Charger.
  2. House loads aboard ship are fed from the Main DC Power Distribution Buss.
    1. A 1-0 AWG red wire runs from the terminal block to a terminal block in the electrical closet. This is the DC attachment point for the ship’s bilge pump, high bilge alarm, NewMar® DC Load Center, BlueSea Systems® WeatherDecktm Load Center, Xantrex® Inverter and shower sump pump.
    2. A 1-0 AWG red wire from the terminal block feeds the vessel’s 70 amp windlass circuit breaker. From the circuit breaker, a 1-0 AWG red wire joins in the electrical locker with an OEM 38mm2 red wire to feed the vessel’s windlass contactor, located forward, in the chain locker overhead.
    3. A #8 AWG red wire feeds a 40 amp circuit breaker which feeds the Garmin® GHP10tm autopilot system.
    4. A fused attachment feeds the Magnum® ME-BMKtm battery monitor module.


  1. Note: Setup options for the Magnum Inverter/Charger and ME-RC Remote Control are found in the MS-Word document entitled “Magnum_Remote_Control_Setup_Customization.doc.”
  2. Note: Setup options for the Balmar ARS-5 external regulator are found in the MS-Word document entitled: “Balmar_ARS-5_Setup_Customization.doc.”
  3. Note: the written description contained in this document is diagrammed in the document entitled ”DC_Electrical_Distribution_System.PDF.” Details of electrical system attachment points are documented in a table entitled “DC_Branch_Circuit_Functions.XLS.”
  4. WARNING: This  disconnect switch removes power from the bilge pump, sump pump and high-bilge alarm circuits. Therefore, it is to be used only for attended servicing of the electrical system. It is not intended for long-term disconnection of the battery bank while the boat is in the water!

Balmar® 110A High Output Alternator:

An alternator is a “self-limiting” device (ABYC E11, 11.4.26). That is, “a device whose maximum output is restricted to a specified value by its magnetic or electrical characteristics.” What that means is that an alternator can only produce just so much output current – in this case, 110A – regardless of how much drive is applied to its field winding. If the alternator fails, output generally stops. For self-limiting devices, a fuse is not “required” by ABYC E11,, but it is a reasonable precaution.

Aboard Sanctuary, the alternator connection to the ship’s DC system is protected by a 200A, Type MRBF, fuse. Two Hundred amps may seem too large a rating. The maximum rated output of the alternator is 110A. The ampacity of the #6 AWG conductor, derated because it’s in an engine space, operating in a 12V system with a 3% voltage drop and 105ºC insulation is 80A, and substantially higher for the 10% voltage drop case. So it may appear there is no scenario where the 200A fuse would protect the alternator connection wiring.

It’s very important to understand that we DO NOT want that fuse to open in the absence of a true, sustained over-current situation. If the fuse were to open while the alternator was operating in its designed power output range, the effect would be to instantly disconnect the electrical load (the battery bank) from the alternator. The magnetic field inside the machine would instantly collapse, creating a very high voltage “spike” inside the windings of the machine. That spike would almost certainly destroy the alternator’s internal diodes and render the device inoperable.

Alternators contain solid state full-wave rectifier diode pacs. Internal diodes prevent DC power from flowing backwards through the alternator when the engine is not in operation. If diodes fail in a welded-closed state – “shorted,” or “short circuited” – the result would create a direct path from the battery to ground via the alternator’s stator windings. The purpose of this fuse is to protect against that true over-current condition. In the case of a shorted diode, the 200A fuse protects the charging wire from becoming overloaded and, thus, a fire risk.

Magnum® MS2012tm Pure Sine Wave Inverter/Charger:

The positive and negative DC wires for the ship’s PSW Inverter/Charger are 2-0 AWG BC5W2 boat cable. Round-trip distance from battery-to-device and return is approximately 10′. The rated ampacity for 2-0 AWG primary wire inside an engine space is 280 Amps DC (ref: Magnum’s MS2012tm specs state that maximum battery charging current is 100 Amps DC, and maximum full load inverter draw at rated AC output load is 225 Amps DC. Optional configuration options are available via the ME-RCtm Remote Control to limit Inverter/Charger operating currents.

DC Return (DC “Ground”):

There are two terminal blocks in the ship’s engine room that comprise the ship’s DC return circuit to the main battery bank. The DC branch circuits and AC Safety Ground are all collected on a terminal block located fwd in the engine compartment, at deck level, starboard. This terminal block is connected to the main DC negative buss terminal block via a 1-0 AWG black wire.

The main DC negative buss is a Blue Sea® Systems 600A terminal block located amidships in the engine room, starboard, above the battery boxes. Joined at the main DC negative buss terminal block are:

  1. the consolidated branch circuit return terminal block, via a 1-0 AWG black wire,
  2. the Magnum® MS2012tm PSW Inverter/Charger, via a 2-0 AWG black wire,
  3. the propulsion engine block, via a 2-0 AWG black wire, (returns the Starter Motor circuit and the Propulsion Engine DC controls, instrumentation and instrument lighting), and
  4. attachment to the battery monitor’s 50mV, 500A measurement shunt, via a 2-0 AWG black wire.

The return connection to the negative terminal of the main battery bank is made from the battery monitor’s 50mV, 500A shunt, via a 2-0 AWG black wire.

Engine Wiring Diagram – Cummins 4B/6B

The wiring of the sensors and controls on a diesel engine in a boat involves several design variables, including:

  1. engine manufacturer preferences and choices,
  2. mechanically injected vs. electronically injected common rail technology platform,
  3. “normally-open” vs. “normally-closed” fuel shutoff solenoid,
  4. manufacturer and package options for gauges/sensors
  5. transmission neutral safety switch variables, and
  6. transmission oil pressure and temperature sensors/gauges, if installed.

The propulsion engine on Sanctuary is a Cummins 4BT-3.9 mechanically injected engine with a normally closed fuel solenoid that requires full-time DC power to keep it open.  The OEM sensor/gauge package is manufactured by VDO and includes tachometer, dual station oil pressure and temperature gauges and audible alarm sounders.  We installed dual station aftermarket high exhaust gas temperature sensors and alarms.

For those owners who perform DIY engine maintenance and repairs, I have included the wiring diagram I prepared for Sanctuary.  For simplicity, this diagram DOES NOT show gauge illumination wiring.  Click the following link to get a downloadable Adobe .pdf copy of Sanctuary’s engine wiring diagram: 20161022_engine_room_instrumentation_terminal_block.  This engine has two different kinds of oil pressure and temperature sensors.  The set that feeds the oil pressure and temperature gauges is analog.  The set that feeds the safety alarms is bi-modal (“on”/”off”).

Although this drawing is specific to the Cummins 4B, I would think it is “typical” of what would be found on many engines.  I encourage all boat owners or develop a wiring diagram of their propulsion engine.  If you ever need it, having it will save the skilled labor cost involved in figuring it out, diagnosing failures and making repairs.

Tripline Use and Cautions

Sanctuary and crew cruise mostly on the US East Coast, where water depths for anchoring in-the-main range from 12 to 25 feet.  Sometimes more, sometimes less, but a working average of 15 feet.  The deepest water in which we have anchored was outside Boothbay Harbor, Maine.  I think our “record” was in water depths of 56 feet at low tide with a 12 foot local tidal range.  These are not big numbers compared to the Pacific NW.

When we anchor, I put out a minimum of 4:1 scope, and my preference is to put out more.   Our rode is all-chain.  That scope is my precautionary approach against something changing in the overnight hours when I may be less alert and too slow to appreciate and respond to rapidly changing/deteriorating conditions.

When we first began full-time cruising, we depended on Skipper Bob Cruising Guides for the Atlantic Intracoastal Waterway (A-ICW).  Skipper Bob suggested using triplines in areas of the Carolinas and Georgia, where underwater hazards included numerous deadfalls and stumps.   The first couple of years we cruised, I avoided anchoring in those areas.  I was afraid of the hassle and unsure of my skill in freeing myself from a snag.  But, we really liked the quiet and beauty of that area, so I decided to build and experiment with a tripline, and learn to use it, so we could feel confident anchoring in that region.

Our “proof-of-concept” assumptions for the tripline were twofold.  First, we knew the tripline would be useful in freeing an anchor snagged on some invisible underwater hazard.  Second, we thought it would signal the location of our anchor to other boaters looking to place their own anchors; “mark our swing circle,” as it were.

I designed our trip line to be self-adjusting to accommodate average East Coast tidal ranges.  One end of the tripline was permanently attached to the anchor, and the fly end of the tripline ran through the loop on a red float ball.  The fly end was permanently secured to a 1# lead fishing weight.  The size of the weight prevented the line from running back out of the float’s attachment loop.  As the tide fell, the weight fell by gravity to hold the ball floating centered over the anchor.  As the tide rose, the weight rose by the buoyancy of the float ball.  That held the ball floating on the surface of the water, centered over the anchor.  The line itself was 3/8″ nylon, 30′ long.  The system worked fine in water depths ranging from 12′ to 25′.  In waters less than 15′ deep, the weight would come to rest laying on the sea bed, but the ball would stay very close to the anchor’s position.

My design worked to keep our tripline float located immediately above our anchor.   Deployment was easy; we just threw the ball over the side after the anchor settled onto the seabed.  Retrieval was also easy; we’d just allow the anchor to come up and then catch the tripline.  Both tasks were easily managed from our foredeck.

I made it a point to use the tripline virtually every time we anchored for about one full cruising season.  That season included a 1400 mile southbound migration from Baltimore to SW Florida, and the 1400 mile return to Baltimore the following spring.  I never did actually need the trip line to free the anchor from a snag.  OK, I grant that’s not valid in evaluating the usefulness of the tripline for freeing a snagged anchor.  The idea of the trip line is for it to be there IF AND WHEN it’s needed.  We can certainly agree, it isn’t going to be needed very often.  However, our “proof-of-concept” trial didn’t work out as well in practice as I had hoped.  While we were using the trip line, we also encountered some significant disadvantages (risks) to having it deployed.

One realization was that the only time a tripline float helps other boaters understand our true swing circle is if wind and currents are up a bit.  In gentle to moderate breeze conditions (Beaufort 3-4), the rode becomes stretched out to the point that the bulk of the rode is lifted off the sea bed in resisting the drag forces on the boat; not taut, but stretched out along its entire length.  But in calm conditions, anchor chain lays on the sea bed.  With the rode laying on the sea bed, the swing circle appears rather smaller than it really is.  That is particularly true in deeper water where the length of the scope triangle’s hypotenuse becomes increasingly significant.

beaufort3    beaufort4

In calm conditions, the boat is typically held to the sea bed by the weight of the chain, not by the anchor itself.  The natural chain-fall location is the point at which the rode comes to rest on the sea bed after relaxing from the mechanical load of setting the anchor.  In my experience retrieving our anchor after a calm overnight, the chain usually comes up in an “S” pattern, formed by the movement of the boat in reversing tidal currents.  The result is that the boat never moves through it’s true swing circle.


In calm conditions, when tidal current reverses after slack, our boat will simply “pivot”  around the chain-fall location.  At that time, the tripline float will be positioned aft of our boat.  In that location, it’s hard for others to even be sure the tripline float is our’s.


As the strength of the flow of the reversed tidal current increases, there will be a time when the chain’s weight alone can’t hold the boat, and the chain gets partially pulled back on itself; that is, pulled away from the natural chain-fall location and towards the position of the anchor.  Thereafter when the tidal current reverses again, the boat will pivot back and be pulled slightly back away from the anchor’s position.  While this is happening, the tripline float often winds up aft of, or alongside, the orientation of the boat on the surface of the water.  Occasionally, we found our float would wind up under our own swim platform, snagged on one of the support brackets.  That never actually caused us to unset ourselves, but it certainly could have.  We have friends on a Monk 36 who unset their own anchor that way, in a t’storm, in the dark, at 03h00.

Furthermore, we discovered the hard way that the presence of the float ball does not stop it from being “run over” by other boats moving through an anchorage.  We had that happen twice in the year of our “proof-of-concept” trial.  Once in Georgetown, SC, a sail boat came through the anchorage looking for a spot; 15h00 on a sunny afternoon.  The person on the bow was fully occupied sorting out his ground tackle, not at all focused on keeping a lookout.  The helms-woman probably could not see our red float ball from her cockpit helm station.  Poof, they ran over our float.  On another occasion in South Florida, we were preparing to depart our anchorage, just before dawn, in pre-dawn low light.  A neighboring boat was a few minutes ahead of us with their departure preparations.  When they motored out of the anchorage, they ran over our float.  Fortunately for us, neither of those incidents snagged our float or unset our anchor.  But no matter our good fortune, had they snagged our float, we would have been the worse for their inattention.

So, it’s only some of the time – probably a relatively small percentage of time – that having a tripline float is actually helpful to others in understanding our true swing circle.

I do not like lying over another boat’s rode and I work very hard to avoid that.  I think most boaters feel that we’d be way too close to them if we were lying over their rode.  I would not want another boat to swing over our tripline ball, because of course, that risks unsetting our anchor.

So it is true that a tripline float can reliably mark the position of the anchor in the sea bed.  Whether that is helpful to me or others is less clear to me.  There are times when it may help, other times when it does not.  The real key to seamanship in anchoring is to honor the location of boats that are already settled in the anchorage.  Stay an appropriate and suitable distance away from others in anticipation of the possibility of fast changing wind and weather conditions.  That decision requires seamanship skills, forethought and high value of personal courtesy to strangers.  Sometimes, it means moving on, which we do if we can’t be certain we have safe swing room.  After all, a t’storm in the middle of an otherwise calm overnight changes all appearances and risk assumptions.  If a t’storm were to move through when the tripline float is snagged under the swim platform, that could easily become a perfect storm of undesirable coincidence and unwelcome outcome.

Conclusion: I gave up on using the the trip line.  Ultimately, I decided the benefits weren’t worthy of the risks.

50A Power from 30A Sources

Facility managers for marinas, yacht clubs, boatyards, condos and municipal walls must make investment choices about the electrical infrastructure that they will install to support their customer’s needs. Systems that provide maximum flexibility in electrical connectivity for boaters are expensive in capital cost and maintenance. In many facilities boaters will encounter more modest wiring alternatives. Wiring configurations will also vary between docks in larger facilities. Different docks at facilities that support a wide size range of both resident boats and transient visitors may be wired differently. Very large boats would normally slip on a dock with other large boats. These docks will likely be powered with only 208V/240V, 50A service outlets. Docks intended for mid-sized boats may have a mix of 208V/240V, 50A outlets and 120V, 30A outlets, or may have only 120V, 30A outlets. Facilities that cater to only transient visitors may have a mix of 30A and 50A outlets, or may have only 20A and 30A twistlock outlets. Electrically, there are many possible code-compliant wiring variations.

Cruisers must assess their personal desire for, and dependence on, shore power. Before departure, cruiser’s should obtain a set of adapters to provide the desired personal flexibility. The specific adapter(s) needed aboard the boat depends on the shore power inlet configuration of the boat. Along the Great Loop route, several variations of shore power may be encountered. The goal would be to have the flexibility to be able to connect the boat’€™s shore power inlet connection to each of the following commonly found power sources:

  1. residential 120VAC, 15A and 20A duplex outlets,
  2. marine 125V, 20A twist outlet (sometimes alone and sometimes in pairs),
  3. marine 125V, 30A twist outlet (sometimes alone and sometimes in pairs),
  4. 208V/240V, 50A marine twist outlet.

We never encountered a 120V, 2-Pole, 3-Wire NEMA type SS1 50A shore power source; they exist, but are very uncommon. We have encountered NEMA 14-50 (residential 240V, 50A outlets used on electric range/ovens and kilns) in various places along the Erie Canal system for use by canal system work boats. Because we had an adapter to access those outlets, we enjoyed shore power when others did not.

Boats fit with 50A Shore Power inlets will regularly encounter situations where 50A outlets are not available. For these situations, 30A-to-50A adapters can provide access to a AC power sufficient to meet short-term needs. Simply put, adapters create options, flexibility and alternatives to boaters. Among the options, adapters can provide enough power to avoid the need to run gensets at a dock.

Note: this article applies to boats which are NOT fit with polarization/isolation transformers.

In North America, the national standard for power delivered to residential and light commercial customers is a “single phase, three-pole, four-wire, center-neutral” wiring configuration. This system is sometimes referred to as a “240V grounded-neutral” system. In these systems, the service’s Neutral (white) conductor is bonded (electrically connected) to the system’s Ground conductor. The bonding point is located at the “derived source,” ashore. Boats connected to shore power systems should never have the neutral and ground bonded aboard the boat. Connections to outlets fed from single phase sources in the utility distribution system will receive service voltages of 120V/240V. Connections to outlets fed from the phase legs of three phase sources in the utility distribution system will receive service voltages of 120V/208V.

Figure 1 shows a typical single-phase residence or dock source fed from a street transformer.  The “secondary” of the transformer is the feed’s source:


Figure 1: Single Phase Transformer with 3-Pole, Center-Neutral Secondary to Customer

Figure 2 shows the common dock power distribution components found on docks at marinas, yacht clubs, boatyards, condos and municipal walls throughout North America. The “derived source” is defined by code to be the point where the Neutral-to-Ground Bond and the dock’s main disconnect circuit breakers are located.

Dock electrical system feeders must be designed to support a number of boats at the same time, which means the current-carrying conductors of the dock feeder need to be quite large. In the US, the National Electric Code, Article 555.12, specifies the ampacity calculations of dock feeders.


Figure 2: North American Dock Shore Power Layout – Typical

Figure 3 shows a simplified example of the most common configuration of 50A shore power outlets found on docks.  This example shows the 3-pole, 4-wire dock feeder with drops to six 208V/240V, 50A shore power receptacles.  The source for the dock feeder can be either 120V/208V or 120V/240V.  This wiring configuration is mandatory in order to support boats fit with 50A shore power services.  Note that the dock feeder is a direct electrical extension of the power transformer shown in Figure 1, and consists of the two energized conductors (L1 and L2), the Neutral conductor (N), and a safety ground conductor, (G).


Figure 3: Typical 240V, 50A, 3-Pole, 4-Wire Dock Feeder

Figure 4 shows a portion of a 120V, 30A shore power configuration.  In this example, each outlet provides 120V at up to 30A to the boat.  Note that adjacent outlets in this wiring configuration are alternately connected to the two energized legs, L1 and L2.  Since both energized legs are necessary for 208V/240V service, this would be the most common way to connect 30A outlets in the case of a dock with a large number of 50A outlets.


Figure 4: Desirable, Best-Case 125V, 30A Dock Wiring Usually Found on Docks with 50A Pedestal Outlets

Figures 5 and 6 show two alternative configurations for providing 30A shore power at a slip.  As in Figure 4, each outlet in Figures 5 and 6 provides 120V at up to 30A to the boat.  The difference in these examples is that all of the 30A outlets are connected to the same energized leg, rather than to alternate legs, of the dock feeder.  For 30A boats, this configuration is functionally equivalent to the example in Figure 4.  Boats requiring two 30A shore power services will never notice or be affected by the difference between the configurations shown in Figure 4, Figure 5 or Figure 6.


Figure 5: Alternate “One” for a 125V, 30A, 2-Pole, 3-Wire Configuration, with Only One Energized Dock Feeder Leg Used for Power


Figure 6: Alternate “Two” for a 125V, 30A, 2-Pole, 3-Wire Configuration, with Only One Energized Dock Feeder Leg Used for Power

For boats that require 208V/240V shore power services via a 50A, 4-Wire shore power cord, a “Smart Wye” splitter can provide shore power from the example shown in Figure 4, albeit at reduced total amperage capacity of 30A, total.  However, the “Smart Wye” will not deliver any power at all if connected to the configurations shown in Figures 5 and 6.

Figure 7 shows the electrical diagram of a “Smart” Reverse Wye Splitter.  To the left are two 30A male plugs which are fit to  30A pedestal outlets.  On the right is a 50A female, which  receives the boat’s regular shore power cord.  In the box at the center, a relay is used to forward power from the pedestal outlets (dock feeder) to the shore power cord.  A 208V/240V relay, K1, is connected between the two energized conductors of the two incoming 120V, 30A lines.


Figure 7: “Smart Wye” Reverse Splitter

Figure 8 shows a “Smart”€ Reverse Wye connected to the dual-leg dock feeder wiring configuration (as previously shown in Figure 4).


Figure 8: Smart Wye Reverse Splitter Connected to Both Energized Legs of a 208V/240V Shore Power Service

This wiring alternative places 208V/240V on the relay coil, K1. The relay “picks,”€ meaning the contacts of the relay close, and this allows 208V/240V shore power to feed through the splitter to the boat. With this adapter, 208V/240V appliances will work. Because the input source is limited to 30A, boat loads may need to be manually limited and controlled to avoid drawing more than 30A. However, with attention, most boat equipment can be used successfully, even if not at the same time.

Figures 9 and 10 show the Smart Wye Reverse Splitter connected to the two alternative single-leg dock feeder configurations. In these cases, since both 30A inputs are connected to the same energized dock feeder leg, there is no voltage between them; that is, zero volts. Since the relay requires 208V/240V to operate, the relay in this case does not “pick,” and no power at all is allowed to pass to the boat.


Figure 9: Both Smart Wye 30A Connections Made to L1


Figure 10: Both Smart Wye 30A Connections Made to L2

In cases where only one energized dock feeder leg is available, the only way to get any shore power at all to this 50A boat – however limited – is with another type of power adapter. Options are available. To understand the options, it is necessary to first understand how the branch circuits aboard the boat are wired.

Figure 11 shows an incomplete but representative view of a 208V/240V boat electrical system. Although I have modified the diagram, credit for the base is to the American Boat and Yacht Council (ABYC), Annapolis, MD. This diagram shows a “typical”€ AC shore power configuration for a boat built with a 208V/240V, 50A AC power system, and found without a polarization/isolation transformer.


Figure 11: Partial View, Representative of a “Typical” 208V/240V Boat Electrical System

The left side of Figure 11 shows the dock feeder discussed above. At the center-right of the drawing, the AC power buss shown in colors is the AC power buss of the wiring of the boat. All boat equipment gets power from the boat’s AC buss via branch circuit breakers. The 120V utility outlets on a 208V/240V boat can be attached to either one of the energized conductors; to L1 alone, or to L2 alone, or some to L1 and some to L2. The drawing shows two utility outlets. The top outlet is fed by L1 and the bottom outlet is fed by L2. Any adapter that’s used to supply some limited power onto a 208V/240V boat must provide that power to both L1 and L2.

Figure 12 shows a 30A-to-50A adapter that will accomplish the goal. Power from one of the energized dock feeder legs is brought through the pigtail to feed both the L1 and L2 blades of the 50A receptacle. Each 50A receptacle blade will have 120V, but because they are fed from the same point, there will be no 208V/240V power.


Figure 12: 30A-to-50A Straight Adapter

Commercial straight pigtail adapters like this are available.  Power is limited to 30A, total.  With this adapter, 208V/240V appliances will not work, but important 120V refrigeration, lighting, entertainment systems and computers connected to 120V utility outlets will be OK as long as the total load is managed to be less than 30A.