Big Waters

2/7/2024: Initial Post

“Big Water” is just “different” than cruising or traveling the natural protection of Intracoastal Waterways, inland rivers and inland canals.  “Big Water” means maybe being out-of-sight of land, the possibility of encountering deeper water and big waves, perhaps prolonged time to reach a “safe harbor,” encountering unexpected and inescapable fog, experiencing unexpected and unforecast winds, being “stuck” out and having to “ride it out,” and just generally, increased anxiety.  “Big Water” DOES NOT have to be a “high anxiety” activity to be “undertaken and survived.”  Nighttime cruising, away from terrestrial “light pollution,” is an opportunity to actually observe and appreciate the “Milky Way.”  Crossing an area of “deep ocean” in the Northwest Channel in the Bahamas reveals colors never seen and never appreciated anywhere else before.  Because they don’t exist anywhere else.  Cruising “big water” offers many “ah ha!” moments.  Admittedly, being out on “Big Waters” is a new challenge for most of us.  They offer us an opportunity to explore our own personal character and mental resolve in dealing with the unfamiliar.

There are three major categories of “big water” boaters will encounter while cruising America’s coastal, Intracoastal and inland river waterways.

1. Very large, open bodies of water on the US East Coast with names that include the words “Sound” and “Bay” (Delaware Bay, Chesapeake Bay, Albemarle Sound, Pamlico Sound, Sapelo Sound, St. Catherine’s Sound, St. Helena Sound, St. Andrew’s Sound, St. Simon’s Sound).   These are all quite shallow, shoal, tidal, estuarine waters characterized by short period, steep-faced, wind driven waves.
2. Various offshore runs in the Atlantic Ocean of the Gulf of Mexico.  These might be routes of convenience or alternatives to using Intracoastal routes.  Because of the geology of the US East Coast “coastal shelf,” these runs are all quite shallow by ocean standards of depth (less than 60 feet), and very shoal, even many miles off the physical coastline.  In these waters, there are two different kinds of waves.  One wave category is the “wind-driven wave” and one wave category is the “ocean swell.”  Ocean swells originate in the deep ocean, in storms many hundreds of miles offshore.  By the time “swells” get to the coast, they have decayed to relatively low-profile, relatively long-period waves that smoothly and gently rise and fall as they pass under the boat.  These waves travel at amazingly high speeds over ground.  Even 10 footers are quite comfortable at a 20 – 25 second period.  Wind-driven waves ride on top of the swells.  They are shorter in period and have sharper (higher angle) wave faces.  Four to six foot ocean swells at a period of 9 – 15 seconds will be quite comfortable to people if the wind component is low.  But even long period swells can be plenty exciting if winds are up, because every n^th wind-driven wave will line up with the face of a swell, and that wave will be a 12 footer.
3. “Lakes.”  The Great Lakes are large enough that they can have unexpected long period waves that result from water oscillating back and forth at low frequency along the axis of the lake (“seiche,” “kelvin wave”).  Lakes are not tidal, but winds can and do create surface currents and surface height variations that can approximate the behavior of tides.  In general, “lake boating” – principally, Lake Simcoe (Ontario), Lake Champlain (New York/Vermont) and Lake Okeechobee (Florida) – is mostly influenced by wind speed and wind direction.  This is also true of smaller lakes (Oneida Lake on the Eire Canal of New York) which can be quite exciting in summertime daily daytime atmospheric heating and cooling cycles.

On “Big Waters,” the combination of surface height changes and wind-driven waves can make for “confused seas” (waves that appear to come from all directions at the same time) to a greater degree than on smaller lakes. Strong currents caused by river flow and/or tidal reversal can and do affect “seastate.”  The areas where that is most evident is in the large East Coast Sounds and Bays, and in particular, where rivers flow into Sounds/Bays.  There is a phenomena called “Standing Waves,” which can be man-made or naturally occurring.  Naturally occurring, they are found where water flows very rapidly over irregularly shaped sea beds with shallow area.  These areas are charted as “rips,” and they can greatly confuse wind-driven waters in the large sounds of the US Southeast.  Examples of areas with significantly confused seas is where the Neuse River and the Bay River come together at Pamlico Sound; another is around lower Manhattan in New York harbor, where the East River joins the Hudson River, and another is in the area of the  “Narrows” (Verrazano Narrows) separating the NY City boroughs of Brooklyn and Staten Island), and separating New York Harbor’s Upper Bay and Lower Bay (Raritan Bay).

The Gulf of Mexico is “big water,” and has seastate components of all of the above.  There is a major geologic “Loop Current” (related to the “Florida Current” and the “Caribbean Current”) in the gulf with an 18 – 20 month wax/wane period that can confuse Northern and Eastern Gulf near-shore waters and affect the course of storm and hurricane weather systems.  The gulf also experiences frequent “upper atmosphere inversions” in the lower mid-altitudes that can create surface winds that weren’t forecast, particularly in the overnight hours.  On the gulf in the late fall through winter and into early spring, there are cyclical cold fronts that roll through approximately every 7 – 10 days.  Those cold fronts bring high winds that roil up the gulf.  And the rule there is like the ocean offshore rule: “Give the gulf a full day to settle down after the wind forecast falls into an acceptable range.”  After 24 -36 hours of winds, it’ll take 24 hours for seas to settle and waves to decay for a comfortable boat ride.  That settled period would be a desirable “weather window” for travel by boat.  In the late spring on the Gulf, weather patterns are very different; daily land heating/cooling cycles create convectional winds (“on-shore” during the morning, as cumulous clouds form, and “off-shore” during the evening, as cumulous clouds collapse and evaporate) .  These strong convections are also associated with PM thunderstorms.  That also becomes the typical, daily “summer pattern.”

Above, I describe “seastate” and “waves” in terms of “wave height” and “wave period.”  NOAA “definitions” of “Significant Wave Height” and “Wave Period” are on NOAA’s website.  NOAA defines wave height as the distance from the bottom of the wave trough to the next wave’s crest.  Those unfamiliar with marine weather forecasts may find the meaning of the numerical quantities misleading.  “Significant Wave Height” is the average height of the largest 1/3 of all waves.  Because the “significant wave” forecast is the average of the highest 1/3 (33%) of the waves, 15% of all waves will be taller than the wave height forecast value.  The math of statistical analysis is progressive, and suggests that about once an hour (about every 1000th wave), a wave that is twice the forecast wave height quantify will be encountered.

To boaters, the comfort of the expected ride is more important than the absolute value of the predicted wave height.  Boaters can predict comfort based on the ratio of wave period to wave height.  People are more comfortable with smooth motion transitions and more gentle, less abrupt, changes in acceleration.  Since sharp, jerky motion is undesirable, wave period becomes very important in determining how the ride will feel, since abrupt, jerky motions are associated with steep, short period waves.  If the ratio of wave period to wave height is 2:1, ride comfort is generally acceptable to most people.  For a given wave height, the greater the period, the more comfortable the ride.  Wave periods shorter than twice the wave height become increasingly uncomfortable as the period to height ratio decreases.

THERE WILL BE TIMES WHEN BOATERS GET “CAUGHT” IN CONDITIONS THAT WOULD BE DEEMED “LESS THAN FAVORABLE,” so boaters are advised to anticipate that can happen, and be prepared for it.