Category Archives: Equipment Topics

Energy Monitor, with a Bonus Use

My Admiral and I live full-time aboard Sanctuary. We cruise in the warmer months. At least twice each year, we stay at the same marina facility for several weeks at a time. We stay at our home yacht club in the spring and mid-to-late fall to stage our departure and return from summer cruises. We migrate south and enjoy our winter season in warmer climes.

For long-duration marina stays, it is common for marina facilities to measure electricity consumption with an electric meter. The marina then invoices the slip holder for actual electricity used, measured in “kilowatt hours,” or KwH.  This is also, of course, residential practice everywhere in North America.

We have observed that rates for electric power vary widely from region-to-region and place-to-place. It is not entirely uncommon to find that the electric meters fit into slip-side pedestals are either not working at all or produce incorrect readings. When this situation is known, the marina typically bills a flat-fee that is equivalent to some “average” for boats our size. When it is not previously known, it can result in interesting conversation with marina office personnel. All of this has caused us to wonder – often – about the actual magnitude of Sanctuary’s “average” electric use.

With the above as background, I recently learned of a company called Energy, Inc., of 648 Marina Dr., Charleston, SC 29492, d/b/a “The Energy Detective,”  This company makes a line of energy monitors, one of which is intended for use in premisis wiring systems in the residential market, and is quite suitable for use aboard Sanctuary.

Sanctuary is fit with two 30A shore power inlets. One feeds the “house” circuits and the other feeds the heat pumps and associated raw water circulator pump and pump controller.

I purchased a TED5000G. This model is meant to monitor power use in one single phase, center-tapped, 240V, conventional on-premises electric service.  This is equivalent to boats with a single 50A shore power service or two 30A shore power services. The TED5000G comes with 1) two clamp-on current transformers, 2) a unit that monitors incoming power and relays status information to 3) a control unit the company refers to as a “Gateway.” This makes for an easy DIY installation. Because the current transformers clamp over the incoming hot conductor of each 30A shore power inlet; that means no fiddling with the inlet wiring is required of the installer.

The TED5000 Gateway box has a wired Ethernet interface that plugs into any 802.11b/g/n capable Ethernet router.  Sanctuary is fit with a Cradlepoint MBR95.  The TED Gateway has internal firmware (Linux, perhaps?) with a web server front-end and a data base back end. Data collected by the monitoring unit (MTU) is fed to the Gateway unit as a digital signal over the existing power lines in the boat.  The transmission protocol is “Power Line Carrier.”  Digital data packets are imposed on the premises (boat) power wiring at a carrier frequency of 132 kHz, and transmitted during the zero-crossing of the 60 Hz AC sine wave.

The TED5000 monitors line voltage in real-time, and collects power usage data. The web server allows access to a real-time display of data from any browser (Firefox, Chrome, Safari, IE) on any computer/PC/tablet/smart phone. The web server has configuration capability, and can be be set up with time/date, electric rate you pay to your electricity provider, billing cycle, local weather, and it allows for differences in prime-time, off-time and seasonal billing rates.

This system is not exactly sophisticated by today’s computer technology. It needs a wired Ethernet connection to a router rather than having an internal Wi-Fi adapter. The internal web server is a tad slow.  However, at a $200 price point, it seems utilitarian. Here’s a screenshot of the real-time “Dashboard:”


This view shows I’m configured for a flat-rate electric billing plan at $0.21/kWh (expensive). The current time is 16h04, and I have 11 days to go in the billing cycle. I’m currently consuming 0.372 Kw of power, and have used 10.5 KwH since midnight last. The current line voltage is 121.5VAC (good), and my average daily usage in this billing cycle has been 14.0 KwH. I don’t have enough experience with this system yet to know if the projections are valid.

Here’s a screenshot of the “History” page.  This page shows actual power usage:


The “Day History” shows my cost at $0.21/kWh; a low of $1.03 and a high of $6.08. The “low” day was dry, clear, mid-70s, boat wide open for 24-hours. The high day was hazy, hot, humid, high 80s, running A/C all day and night. The “Hour History” shows the heat cycling on in the overnight last night; 52ºF this morning.  So, the data all correlate and make sense.

Now for those that think the story is over, stay with me for a minute. There’s more than just power usage and cost tracking for the boat owner here!

I was most impressed to discover this little monitoring system could also tell me a lot about the health of my shore power connections.  Following is a screenshot of the “Graphing” tab. The blue line shows power usage, and the red line shows incoming AC line voltage.  The settings for this graph reflect a data sampling interval of once-a-second (“Second Live View”) and the total time duration of this graph is 30 minutes. This screen shot was taken during dinner preparation a couple of days ago. The admiral was doing pasta in the microwave. Here’s the raw data:


And here’s what was happening:


There are several noteworthy observations reflected in this graph:

  1. as the power stair-steps up, the line voltage stair-steps down. Why? Is that OK, or not OK?  Well, er, ummm…    not!
  2. the battery charger decided it needed to be heard from; who knew?  Yes, that is a pattern with our inverter/charger; It does come on when line voltage dips, although there is no DC load that appears to correlate with the charger activation.
  3. the line voltage is sampled from the 30A AC inlet that feeds the “house” power panel, which powers the microwave and the battery charger.  The heat pump is on a 2nd 30A AC shore power inlet. Since the heat pump cycling “on” did not result in a corresponding dip of the line voltage, doesn’t that suggest the voltage drop implicates the boat’s “house” AC shore power service, and not the marina’s dock feeder cable to the pedestal?  Hmmm…

Investigation of item 3 ensued forthwith.  I “shot” the pedestal 30A shore power breakers with an infrared (IR) thermometer, and they were getting warm with load.  Faced with this graph, it’d be hard for the marina to conclude that a boat owner doesn’t know what he’s talking about. The marina promptly changed-out the pedestal circuit breakers.  Some improvement, but not enough.  So, we’ll next change out the pedestal 30A sockets.

Now here’s the pearl at the end of this story.  It’s obvious the line voltage measured at the “house” shore power panel on the boat is dropping.  I was unaware of it.  There were/are no symptoms of that voltage dip that I could observe without this graphing function.  It may have been noticeable with a digital voltmeter, but I have an analog meter on my “house” panel.  Even if I could have seen it, it would have been much harder to convinced the marina to take action

One final note on “Power Line Carrier” technology.  From the TED troubleshooting guide: “Today’s homes usually contain numerous devices capable of producing noise on the power line. These include fluorescent lights and ballasts, halogen lights, UPS back-up power supplies, unfiltered dimmer switches and fan speed controls and A/C–D/C power supplies for fax machines, computers, televisions, printers, WiFi devices, and numerous other electronic products.”

Aboard Sanctuary, the only interference we experience is related to 120V dimmers that control 120V halogen lightbars located in the galley and salon.  When those lightbars are “on,” data transmission between the MTU and the Gateway is interrupted.  Sanctuary’s  inverter/charger (Magnum MS2012), in passthru mode, does not interfere with TED5000G data transmission.

So, yes, I like my TED5000.


Pixie and Sprite Boat Monitoring System

In the spring of 2012, I saw an article on Panbo (look here: about a pair of boat monitoring systems called “Pixie” and “Sprite,” by Siren Marine (here:  Then while cruising in New England during the summer of 2012, we stopped at a marina that had an advertising handout on the device.  I had been interested in boat monitoring systems for some time, but was never very excited with the price-point vs. feature-set alternatives.  At the Annapolis Boat Show in October, 2012, we happened to see the Siren booth.  We had a chance to touch ’em, see ’em in operation, meet the owner/developer, etc.

I bought the “Sprite” version.  It uses GSM cell technology, via a SIM card, to send text messages to a smartphone and provide information about the status of the boat.  It will transmit pre-scheduled status and real-time alarm info.  It monitors bilge pump activity, battery status, hi/low/current temperature and shore power status.  Additionally, it provides several normally open (n/o) and normally closed (n/c) relay contacts.  With these contacts, it can:

  • monitor bilge pumps and high bilge alarm switches,
  • turn heat pump units on/off remotely, via text message,
  • turn deck lights and/or anchor lights on/off remotely, via text message,
  • monitor fire/smoke/CO alarms and motion detectors remotely, via text message,
  • monitor reed-switch door and window intrusion alarm switches,
  • etc., etc.

The Sprite has an internal GPS, so it can monitor unauthorized boat movement as well as provide a real-time Geo-fence while you’re on the hook.  This is useful to monitor for anchor dragging.  I’ve done a fair amount of research on boat monitor units, and this one seems to be very good value for the price.

Like a cell phone, you buy the “Pixie” or “Sprite” hardware unit and an associated text messaging plan.  The text messaging plan (2G, machine-to-machine) is used to transfer boat status data to your smart phone.  The price point included a one-time-charge (OTC) of $600 for the “Sprite” box (the “Pixie” is $500, but doesn’t monitor shore power), and $15/month charge for unlimited text messaging.  (A Boat Show promo added to the length of warranty and added three months of complimentary text messaging.)  With its feature set and price point, it’s much more attractive than Boat Nanny and GOST.  The SPOT HUG has apparently been discontinued (verify that for yourself); it didn’t have a very rich feature set by comparison to available competitor offerings, and rumor seems to suggest it didn’t work all that well.

Installing the “Sprite” was quite easy as a DIY project!  With real-time monitoring of shore power, battery, bilge and temperature, I feel comfortable leaving Sanctuary unattended in the water, particularly at a staffed marina.  We live aboard, and Sanctuary is our home.  When we’re away from the boat visiting our kids, we do worry about her.  We always leave someone in charge when we’re away, and we also notify the marina office.  We’ve never had a problem.  But with the monitor, we have real-time awareness if something looks wrong, and can intervene before it becomes catastrophic.  My thinking is, if I got an alarm, I could call a dock neighbor or the Marina staff to check it out.

For us, Sprite takes some of the anxiety out of being away from the boat.  It could also simplify haul out issues and commissioning/decommissioning work and expense, so there are multiple ROI opportunities.  Rumor has it these units MAY provide an insurance discount (depending on company).  If so, there’s an additional ROI opportunity to installing one.

Fire Detector/Smoke Alarm

Aboard Sanctuary, we use First Alert® smoke detector units that I bought at Lowes.  I recommend the detectors that have *both* micro-particulate and ionization sensors.  They detect combustion particles from microscopic incipient fire on up to visible smoke.  They use a 9V “transistor radio” battery.

I located one in the vee berth, one on the master aft cabin, and one on the overhead (the ceiling) of the electrical closet.  The single most likely place to have something start without occupants being aware of it is in that electrical closet.  The alarm sounder on the First Alert is plenty loud enough to awaken a sleeping person.

First Alert and other manufacturers make detection systems in which if any one unit detects something amiss, it sends a wireless signal to cause all of them to alert. That would be good for boats under way, and for larger boats.

Most of the home units are rated for 100ºF.  That rating is not sufficient for the boats engine room, although I think it would work.  It’s also not enough for most garages in Florida.  Further investigation required.

We have found that when using the oven for baking (lasagna, breads, etc; anything that takes more than about 1/2 hour), our vee berth unit will alarm.  There’s never any visible smoke, so it must be the ionization sensor, but it does sometimes go off.  We manage it when it happens.  If we keep the boat opened up while baking (not too hot or cold for the boat to be open), it doesn’t happen.

We also have CO sensors.  The CO sensors are made by Kidde®.  These units are powered by 120VAC, but also have 9V battery backup in case we lose AC power.  Since our utility outlets are powered by our inverter/charger, that rarely happens.  We have located the CO detectors in our vee berth and in the master aft cabin, at the level or our bed pillows above the cabin sole.  They are the type that shows CO ppm, numerically, in an LED window.  They never show a non-zero reading, either from the main engine with the boat closed up, or with the genset running.


Faraday Cage

A “Faraday Cage” is a metallic enclosure that surrounds people and sensitive electronic “gadgets,” “gizmos” and “gilhickies” to protect them from damaging stray electrical discharges (electrostatic discharge) that might accompany nearby lightening strikes occurring in a thunderstorm.  For example, a car can act as a Faraday Cage.  The car protects the people in it from electrical discharge.  If stuck on a bridge in a thunderstorm, stay in the car!  The metal skin of the car struck by lightening will lead damaging stray electrical energy away from the car’s occupants.

On a boat, a number of possible Faraday Cages are available to protect sensitive electronic devices and electronic memory cards from possible damage. The bake oven in the galley of a boat can be utilized as a Faraday Cage.  Disconnect your computer from power and from all peripherals, and place it – alone and unconnected – in the oven.  The metal enclosure of the oven will protect the computer from any stray electrostatic energy that might otherwise damage memories or circuit boards.

Your microwave oven can also act as a Faraday Cage.  Place your fully disconnected iPad, Android tablet, eReader, camera and/or cell phone(s) in the microwave during a thunderstorm.  The metallic enclosure will protect these sensitive devices from any stray electrostatic energy that might damage them.

A metal 1-gallon paint can can act as a Faraday Cage.  Place your hand-held VHF Radio, your hand-held GPS, your USB thumb drives, your back-up hard drive and any camera memory cards in a metal paint can.  The can will protect them from stray electrostatic energy that might otherwise damage them.  Of course, you can also use a metal ammunition container, commonly available at sporting goods suppliers.

The entire boat can also be set up to conduct electrostatic energy to a ground plate.  That will route electrostatic energy safely into the water.  This involves interconnecting all of the boat’s stanchions, railings, stays, shrouds, mast (if metal), boom (if metal), deck hardware (Samson Post, anchor rollers, anchor chain, boom crutch), decorative rail guards, etc, etc, etc, with #6 AWG or larger electrical conductors.  This network is in-turn connected to the boat’s ground plate(s).  These items – when methodically interconnected – create an enveloping shell (a Faraday Cage) around the exterior of the vessel, and ultimately act to protect occupants in the same way a metal shell of a car does.  The Faraday Cage routes stray electrostatic discharges  around, rather than through, the living areas of the boat where people and pets huddle up during thunderstorms.  As you might imagine, this is vastly more easily accomplished at OEM fabrication-time for the boat, because the large conductors can be imbedded in the fiberglass and otherwise routed in conduits and/or protected and hidden.  It is greatly more expensive and difficult to retrofit such a system.


EPIRB/PLB vs Satellite Messenger/Communicators (SPOT)

Editorial revisions: 1/20/2016

True Personal Locator Beacons (PLB) operate on “official” GMDSS/SOLAS radio frequencies to communicate with the international, government-operated emergency satellite network.   PLBs have some limitations compared to Emergency Position-Indicating Radio Beacon devices (EPIRB), but use the same satellite communications network.  This system is monitored by government (often military) emergency response agencies.

The SPOT device by SPOT, LLC and the InReach device by DeLorme, Inc., are referred to as “satellite messengers” or “satellite communicators.”  These devices also communicate with satellite networks, but those networks are privately-owned and operated.  Their “911” emergency feature is routed to a privately-owned and operated emergency control desk.  What is important to understand is that the SPOT and InReach devices are not GMDSS/SOLAS-compliant EPIRB-class devices.

Aboard Sanctuary, we think of “risk” as a balanced relationship between the “probability” of an adverse occurrence and the “impact” that adverse occurrence might have on us.  If “probability” is high, but “impact” is low, we might adopt only minimal risk avoidance measures.  If “probability” is low, but “impact” is catastrophic, we adopt much more intensive risk avoidance and mitigation plans.

Our risk analysis starts with highly personal assumptions about how we cruise aboard Sanctuary.  We assume that we travel unaccompanied only in near-coastal, intracoastal and inland river cruising situations.  For our occasional “offshore, out-of-sight of land” transits – the Gulf Stream from Florida to the Bahamas, crossing offshore between locations in the Bahamas, crossing Lake Michigan, and crossing the Gulf of Mexico from Carrabelle to Tarpon Springs – we have traveled with a trusted buddy.  Although East Coast coastal cruising is technically “offshore” in the Atlantic, its rarely more than a few miles; maybe 10 miles along most of the Southeast, and maybe three miles off New Jersey and the New England coast.  In those costal situations, and in the Chesapeake and Delaware Bays, we virtually always have cell service, and we always have VHF radio coverage.  So, for the purposes of this post, we do not treat the Eastern seaboard coastal Atlantic as “offshore.”

Aboard Sanctuary, we do not choose to carry an EPIRB device.  We do choose to carry a SPOT satellite messenger.  For near-coastal, intracoastal and river cruising in North America, we find our SPOT device to be extremely reliable.  Furthermore, it does offer some day-to-day usability advantages that are not present with true GMDSS/SOLAS PLBs or EPIRBs.  The SPOT messenger is not an EPIRB, but comparing satellite messenger/communicator devices to EPIRBs and handheld PLBs, the pros and cons net out within our range of acceptable risk tolerance.

The pros of a messenger/communicator, and specifically our SPOT device, are,

  1. they get location information from the GPS constellation of satellites, and use the  GlobalStar satellite network for message communications,
  2. they are fully independent of cellular system and VHF-Radio range limitations,
  3. the GlobalStar network offers excellent coverage in the Western Hemisphere, and certainly throughout all of North America,
  4. SPOT offers “routine,” “send help” (Pan Pan) and “911 emergency” (SOS) satellite-based message categories,
  5. SPOT gives us daily “we’re here and safe” communications to family and friends,
  6. SPOT offers an optional automatic tracking mode (which we do not use),
  7. SPOT offers a 24x7x365, staffed, emergency command center to handle SOS/life-threatening (911-type) emergencies,
  8. these devices are generally more affordable than EPIRBs,
  9. our SPOT messenger account is linked to our BoatUS Tow Boat account for “send help” messages (and we now know that facility does work).

Sanctuary’s SPOT device (1st Generation messenger) has 3 “AA” lithium-ion batteries.  The batteries are available almost everywhere, and changing the batteries is self-serve.  Since I use the unit every day, I know from day-to-day that it’s actually working.

The cons as we understand them for satellite messengers/communicators, and specifically for our SPOT, are:

  1. they are not automatic; that is, not activated by physical dis-orientation or immersion in water,
  2. they do not use the World Wide GMDSS/SOLAS satellite network; because they are based on the GlobalStar satellite network, there is the possibility of a delay (up to 20 minutes) if a GlobalStar satellite is not “overhead” at the time an emergency signal (“Send Help” or “911”) is activated,
  3. they are not registered with a governmental GMDSS SOLAS SAR authority; thus, SAR dispatch may be delayed because an emergency signal must first be received by the SPOT Control Center, the appropriate SAR authority identified, and then the emergency information referred to the appropriate SAR authority by the SPOT Command Center,
  4. they are rated for immersion for only a few feet and for only a short period of time.

For near-coastal, intracoastal and inland river cruising, a messenger like SPOT or InReach provides capabilities that are well within our personal range of risk tolerance.  We plan our travel for daylight hours and do not travel over night.  We try to avoid traveling in risky weather, particularly when thunderstorms are forecast.  We use our SPOT every day to communicate with family and friends.  To our knowledge, we have never had a prolonged satellite delay or anything nearing a 20-minute delay on message transmission; we mostly have responses from the SPOT website within one minute or less.  We have once used SPOT to file a help call with Tow BoatUS, and on that occasion, it worked absolutely flawlessly.  Of course, so did the BoatUS cell phone app in that case, although the VHF radio (VHF16/VHF13) did not because the local BoatUS operator was still in bed that early morning.

Some newer generation devices in the messenger/communicator market offer custom text messaging with each use.  Some people may find that feature to be useful.  We could update our equipment to get that feature, but we do not feel it’s necessary for us.

At the start of our long cruises, we file a general “float plan” and approximate travel schedule with trusted “emergency contacts.” Our emergency contacts receive notification messages direct from the SPOT website.  We, ourselves, receive each SPOT notification message via email direct from our SPOT account.  We re-forward our daily SPOT messages to inform a larger group of friends and family who “follow” our travels.  Those daily forwards also contain our “chit-chat” about our current weather outlook, vessel status and operations conditions, and our near term upcoming travel plans.  We find this practical and usable.

Finally, if personal risk tolerance requires a higher level of risk aversion aboard, EPIRBs can be rented from BoatUS for occasional use.  Renting ameliorates some, but not all, EPIRB cons.


Automatic Identification System (AIS)

  • Article date: 3Q2013.
  • Detail added, editorial revisions: 2Q2014.

The Automatic Identification System (AIS) is a complex and sophisticated system of marine navigation technologies with several underlying deployment methods.  AIS is intended to assist the watchstanding officer responsible for the helm of a vessel.  In two principle forms, it is used across the entire range of vessel sizes, from the world’s largest cargo ships to outboard fishing boats and canoes.  It is used on the open ocean and in the world’s busiest harbors.

AIS “transponders” are two-way VHF radio devices fit with internal GPS receivers.  AIS transponders exchange information about the host vessel, the present voyage and current operations with AIS-equipped land stations and other vessels.  Citizens, and certainly boaters familiar with AIS, usually think of AIS as a “Navigation Safety Tool,” which is the purpose for which the technology was originally developed.  However, there has emerged since 9/11/2001 a significant interest in AIS by US Homeland Security, federal, state and local policy-making politicians, and many local law enforcement agencies who believe AIS is an appropriate tool to use to track all vessels on US waters. These two uses represent dissimilar, competing interests.  Citizens should understand that  these interests are not the same, are not mutually compatible with current technologies, and can easily lead to mutually contradictory use and regulation.

In general, Class “A” AIS transponders are designed for the needs of large commercial vessels.  Class “B” AIS transponders address a more narrow standard, assumed to be appropriate aboard pleasure craft.  Marine VHF Radio channels 87B (161.975Mhz) and 88B (162.025Mhz) are reserved for use by the AIS “system.”  These channels broadcast the VHF “Data Link” consisting of many different unique inter-system messages.   Class “A” transponders have VHF internal radios that transmit at 12.5 Watts, providing a nominal range of  20 – 25 NM.  Class “B” transponders have internal VHF radios that transmit at 2 Watts, providing a nominal range of 7-8 NM.

To avoid “stepping on” each other, the AIS system uses a variety of time sharing technologies, known as a group as “Time Division, Multiple Access” (TDMA).  The TDMA specification defines 4500 individual time periods per minute.  The total duration of each time slot is 26.5 milli-seconds (ms).  TDMA technologies used in the AIS system include:

    • Self-Organized Time Division, Multiple Access (SOTDMA)
    • Fixed Access Time Division, Multiple Access (FATDMA)
    • Random Access Time Division, Multiple Access (RATDMA)
    • Incremental Time Division, Multiple Access (ITDMA)
    • Carrier-Sense Time Division, Multiple Access (CSTDMA)

In units using SOTDMA and RATDMA algorithms, the receiver listens simultaneously to both AIS VHF channels and makes a map of all the time slots on the composite VHF data link (VDL).  Some AIS messages are longer than others, and require more than a one single time slot in the VDL.  The unit uses the slot map to locate the needed number of adjacent, free times slots in which to send its complete message, and sends its message when that set of slots rolls around.  This is ideal for many applications because it does not require reservation of slots by a base station.  Thus, the schema is not dependent on base stations (not many base stations in the open ocean).  Class “A” shipboard AIS uses SOTDMA.  Class “B” AIS uses CSTDMA.

In the TDMA schema, SOTDMA units receive priority in time slot allocation, so Class “A” AIS is guaranteed an assigned time slot.  Class “B” CSTDMA units listen for the absence of a signal on the transmit frequency on a slot-by-slot basis.  The absence of a signal in any given time slot implies that the time slot is available.  If available, any Class “B” CSTDMA unit can “jump in” and transmit its message.  However, CSTDMA is a “free-for-all” schema; if only one Class “B” unit transmits during a free time slot, that message will be heard throughout the system.  If, however, two or more Class “B” units transmit at the same time, the result is known as a message “collision.”  In high traffic density locations, message collisions can result in lost messages.  Delivery of Class “B” messages is not guaranteed in the TDMA system schema. 

The AIS VHF Data Link (VDL) also supports floating and fixed Aids-to-Navigation (AtoN), such as floating buoys and lighthouses, meteorological and tide level sensors, and satellites carrying AIS.  Messages types used for remote monitoring and control of such aids are used to receive and disseminate information about their location and operational availability to ships transiting nearby.  AtoNs generally use RATDMA, and are guaranteed time slots in the system.  This adds to the message traffic with which Class “B” users must compete.

In the Fall of 2013, the worldwide AIS message structure consisted of 26 different message types, called sentences.  The three most common sentence types transmit 1) permanent information describing the host vessel (its name, vessel type, country-of-registry, registry number, etc), 2) dynamic information describing the host vessel’s current voyage (last port-of-call, current operating status, etc) and 3) real-time navigation information about the current operation and status of host vessel (position, speed, direction-of-travel, rate-of-turn, etc).

Class “A” transponders transmit navigation and vessel identity information more frequently than their Class “B” counterparts, and also transmit on both VHF channels.  Class “B” transponders transmit information at longer-separated intervals, and some Class “B” units transmit on only one of the two AIS VHF channels.

AIS Message Transmission Timing

AIS Message Transmission Timing

AIS receivers do not transmit information about their host vessel, but they do receive information from other vessels and AtoNs.  Receivers and transceivers are available with built in single-channel and dual-channel options.  For those interested, detail on AIS message structure (format) and content (data) can be found on the US Coast Guard site, here:  Significantly more technical detail can be found here:

Only a small percentage of all commercial vessels are actually required by law (IMO Treaty) to carry AIS transponders; large vessels over 300 gross tons, some large tows, and some passenger ships.   The US Navy does not use it, which is potentially problematic in all US East and Gulf coast ports, certainly the St. John’s River, FL, the St. Mary’s River, GA, and the southern Chesapeake Bay, VA.  The US Coast Guard uses AIS only very selectively, mostly on small patrol and “swift boats,” and not always there.  Many tow vessels do not use AIS.  Few commercial fishing boats use AIS.  The Staten Island Ferry in New York Harbor and many swift ferries in large harbors do not use it.  Some ports in the US have adopted port-specific AIS carriage requirements as part of port, maritime facility, vessel and offshore platform security programs.  Some fixed “ground facilities” use AIS, such as Vessel Traffic Services (VTS) monitoring stations and other controlled waterways, AtoNs, and SART units.  Some orbiting satellites carry AIS tracking equipment.  So, AIS deployment and use varies greatly from place-to-place and waterway-to-waterway along the US east coast, the gulf coast and the inland river system, and certainly varies in Canada, the Bahamas, the Caribbean and offshore.

AIS aboard pleasure craft is undeniably a cool toy.  It is growing in popularity and mystique, and does provide a means for owners to display their wealth.  However, I do not believe that AIS transponders are generally appropriate for wide-spread use aboard pleasure craft.  I am not pursuaded that AIS actually assists the pleasure craft “watchstander” achieve “increased safety” in the vast majority of pleasure craft applications.  Furthermore, many AIS transponders aboard pleasure craft simply serve to pollute the VHF radio channels (87B, 88B) with unnecessary transmissions, and can wind up intermittently frozen out of the capacity of the TDMA system in busy traffic areas.

A competent captain maintains a continuous and effective visual watch at the helm at all times while under way.  This is good seamanship and a requirement of US Coast Guard navigation rules.  Electronic position data about other vessels is generally unnecessary to pleasure craft captains who maintain even a cursory visual watch.  With an effective visual watch, captains will have many miles of visual and situational awareness of approaching vessels of whatsoever kind, and ample time to plan safe passing courses.  This is especially true at sail, trawler and cruiser speeds.  In busy harbors, like Annapolis, MD, there are many different boats moving at many different speeds in many different directions at any one time; that is, way too many for the captain to take the time to take eyes off the water to identify and interpret visually on an electronic display of AIS targets.  In Maine in heavy fog, we found many sailboats fit with AIS.  They had power for their AIS transceivers, but did not answer their VHF radios when called to arrange safe passage.  So, something grossly wrong with that picture, and certainly not an effective use of AIS.

Because of the relatively long (30 seconds minimum) update intervals with Class “B” AIS, vessels with Class “B” transponders are almost always not where they are shown to be at a receiving vessel’s chart plotter or electronic display console.  Again because of the long update intervals (6 minutes minimum), pleasure craft can be past you before you see the vessel’s name on your chart plotter/electronic visual display.  Since the “real estate” on a chart plotter/electronic visual display device can be quite limited, the greater the number of vessels that are transmitting, the more visual “clutter” occurs among the many targets presented to the operator if the receiving display.  Much time and attention is required of the operator to absorb and interpret the clutter.  The usefulness of a proximity monitor is dramatically reduced.  Inevitably, the operator spends less time with “eyes on the water,” where they should be in order to “maintain a proper visual lookout.”  And of course, of the total number of pleasure craft running around on a sunny summer afternoon in Annapolis, today, only a small minority (thankfully) have AIS anyway.  The net is, especially in the hands of captains who do not understand the limits of the technology, the tool can create over-confidence and a false sense of security.  The tool can be more of a distraction than an aid!

For pleasure craft owners/operators, there are also potential personal security “downsides” with AIS.  A vessel anchored in a remote location while transmitting position information is advertising their position to anyone with an AIS receiver, including several free smartphone apps.  That information could certainly be of interest to persons with nefarious intent.  Furthermore, do not assume that a pleasure craft using a Class “B” AIS transponder will necessarily be seen on the Electronic Chart and Display Information System (ECDIS) aboard the bridge of a commercial ship.  The software aboard some commercial vessels can be set to suppress the display of Class “B” transponders in order to allow the watchstanding officer to focus on other large, Class “A,” targets and commercial traffic.  And anyway, commercial vessels in charted sea lanes and formal Traffic Separation Zones will not divert their course for pleasure craft.  It is the responsibility of pleasure craft to avoid large ships.

Given the above as “general observations,” I do assert that pleasure craft used as long range cruisers can definitely benefit in some situations from having an AIS transponder in operation aboard.  For those applications, I recommend Class “A” rather than Class “B” AIS units.  I also recommend a transponder that supports the “quiet mode”/”silence” function.  Transponders operating in quiet mode do not transmit data; they act as receive-only devices.  In “quiet” mode, they do not routinely contribute to VHF pollution, do not compete for TDMA time slots, and do not result in the unnecessary distraction of other waterway users.  For routine, day-to-day operations in visual conditions, I recommend using the transponder as a receiver, in “quiet” mode.  I suggest captain’s treat the use of the “transmit” mode as an exceptional situation, reserved for use:

  1. in visibility less than 1 mile (fog, t’storms),
  2. in nighttime operations,
  3. while operating on the inland river system, or
  4. while on offshore passage. 

These above are, after all, the situations where use of the tool may actually increase safety.

Vessels required by law to carry AIS are required to leave them on 24x7x365, even when at anchor or tied up in port.  There are no pleasure craft required to carry AIS, so there is never a time when pleasure craft are required to leave AIS units transmitting when secured in a slip in a marina.  It’s poor courtesy and bad seamanship to do so.  We therefore ask, please, turn transponders to “quiet mode,” or “off,” when the boat is secured in a slip in a marina!  A boat in a slip in a marina is not a navigation hazard to anyone or anything An AIS transponder on such a vessel is just a VHF polluter.

For pleasure craft generally, our recommendation continues to be to fitup a dual-channel AIS receiver.  Sanctuary is fit with an ICOM® MXA-5000™ dual-channel AIS Receiver.  The AIS receiver shares an antenna with our back-up ICOM® IC-M504™ Marine VHF radio.  The ICOM® receiver has a built-in transmit/receive relay.  We are very happy with this arrangement.


Cleaning the A/C Raw Water Loop

Aboard Sanctuary, our normal summer and winter locations are mostly in brackish waters.  Local water temperatures rise into the mid-to-high 80s in the summer months.  Routine preventive maintenance is required to avoid the build-up of sea growth in the raw water circulation plumbing system.

The water that is circulated through heat pump plumbing systems is not biologically sterile.  It is drawn from the environmental water in which the boat is floating.  That water is referred to as environmental, or “raw” water.

All freon-based heat transfer systems work basically the same way.  In their cooling mode, heat is absorbed from the air in living spaces into the freon gas inside the sealed air conditioner system (R-12, R-22, R-134A).  The heat is transferred again from the internal freon gas through the metal walls of the unit’s heat exchanger into the circulating raw water.  The heat is discarded overboard, carried by the discharged raw water.  In their heating mode, heat is absorbed from the environmental “raw” water through the metal walls of the unit’s heat exchanger into the freon inside the sealed system.  That heat is transferred again within the unit into the air in the living spaces of the boat.

The maintenance issue in systems that circulate environmental “raw” water becomes the efficiency of heat transfer into and out of the circulating water.  The efficiency of the transfer of heat into and out of circulating raw water can be impaired by any accumulation of slime, algae and other biological “critters” attached to, and living on, the internal surfaces of raw water plumbing system components.  At its minimum, slime acts like an insulating blanket which impairs heat transfer.  In its worst case, it can build up to the point that it also occludes the lumen of the plumbing through which raw water circulates, acting like an insulating blanket AND decreasing water flow through the system.

To clean environmental biologicals from raw water plumbing fouled with sea growth, a couple of approaches can be tried, in order.  Raw water circulator pumps are high volume, low pressure pumps.  As a first step, if you have the capability to do so, close the intake thruhull, and swap a relatively higher pressure dockside fresh water hose to the raw water loop to the heat pump.  Do this just “downstream” of the circulator pump; i.e., at the discharge port of the pump.  The higher pressure of the dockside water may be sufficient to blow fouling material out of the raw water cooling loop system.  If this works, it’s less harsh than circulating chemical cleaning agents in the system.  If not, though, remove the dockside water hose and restore the circulator pump connection.   Re-open the cooling water thruhull, and prime the pump.  The next step is to place pool chlorine or bromine high test hypochlorite tablets (HTH) into the sea strainer basket.

Aboard Sanctuary, to control the growth of slime, algae and other sea life in the “raw” water loop of our two air conditioning heat pumps, we have used HTH pool “chlorine” tablets for several years.  The tablets are about the diameter of a Kennedy half-dollar, and about 5/16″ – 3/8″ thick.  We put as many of them as will fit into the sea strainer basket that supplies “raw” water to the air conditioners, and we then just run the units as normal.  These HTH pellets dissolve over 24 – 36 hours.  HTH works by releasing elemental oxygen into the raw water.  The elemental oxygen is a powerful oxidizing agent that kills and shrinks slime and other sea-life critters in the raw water loop. That allows the little corpses to slough off of internal plumbing surfaces and flow out of the system.  Physically clean surfaces allow better contact of raw water with the internal metal parts of the condenser/evaporator (cool/heat respectively) coils of the air conditioning unit, which increases heat transfer efficiency.

We perform this preventive maintenance procedure once or twice per season.

We do not use the HTH tablets in our genset or propulsion engine cooling circuits.  Doing so for the genset and the propulsion engine(s) would require them to be running to circulate the chemical.  With engine(s) not running, no raw water circulates and no cleaning would occur.  Also, the efficiency of heat transfer is not an equivalent issue with engines, and is not necessary, in engine cooling systems.

I hasten to add: “not necessary, in my opinion.”  There are significant design differences between air conditioning/heat pump raw water cooling systems and an engine’s raw water cooling system. In air conditioning systems, water flow is constant over a relatively small heat transfer surface area. Furthermore, in the first few minutes of operation, the temperature differential normalizes to a very steady state. Contact efficiency is very important to heat transfer. In engine cooling systems, flow is variable (with engine speeds) over a relatively high surface area. In engine systems, the amount of heat shed in the raw water cooling circuit varies widely, and the proportionate temperature differential is much higher. In engine cooling systems with high temperature differentials, the importance of contact efficiency is lessened. By and large, the capacity of engine cooling systems is significantly over-sized with respect to their nominal operating requirements. That large capacity accommodates extremes that may be encountered in severe operation.  Again, there is no analog to those severe operating conditions in air conditioning system design. So, the two systems are very different.

One common misconception is that calcium deposits will foul air conditioning and engine cooling systems. That is largely an “old wives tale,” often implied and promoted by product advertising. Yes, there are minerals in solution in sea water. Yes, those minerals can and do coat internal hose and metal lumen channels of raw water loops. But except under the most extreme situations, mineral deposits do not account for significant fouling of marine cooling systems. If they did, salt water would be a severe and ever-present disaster. Slime, algae, sea worms and barnacles – living sea creatures – are the problem. These critters grow quickly in warm sea water, foul plumbing lumens and impair heat transfer. It just so happens that de-mineralizing agents – RydLyme®, Lime-A-Way®, muriatic acid, hydrochloric acid – will also clean out slime, worms and dissolve the shells of barnacles and other sea critters. But, these agents are caustic in varying degrees to the internal metals of raw water-carrying loops, caustic to use safely, caustic to dispose of properly and safely, and generally “overkill” on a “fitness-for-purpose” scale. Free elemental oxygen, like that released by HTH, will kill biologicals without adversely affecting hoses, tubing, copper/nickel metals, etc. and they are generally safer for people to use and dispose of safely.

It is my opinion that HTH is the best first-use agent, and I suggest it as the primary, routine course of preventive maintenance. Reserve the caustic stuff for the less common, more intense and serious, corrective-action situations.