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Old 04-07-2001
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Don Casey is on a distinguished road
How We Define Seaworthy


You can't judge a vessel's seaworthiness by its manufacturer; design characteristics determine a vessel's seakeeping ability more so than its construction.
Some time ago SailNet citizen Wayne Wilson of Virginia wrote to inquire about the issue of seaworthiness when applied to modern production sailboats. Specifically, he wondered if there were any tangible evidence to support the frequently heard opinion that "a Beneteau, Hunter or Catalina [is] not up to an Atlantic crossing, but a Hylas, or Hallberg-Rassey, or Cabo Rico is?" Wayne was looking for something more substantial than "vague opinion, arm waving, and sentimentality."

I do my best to make sure that my opinions are never vague; wrong maybe, but not vague. It's a start.

The problem with seaworthiness is that the term means different things to different people. Is a canoe seaworthy? Presumably everyone that buys one thinks so. Of course, that is predicated on using the vessel in relatively benign waters. If your canoe sinks on the way to Bimini, there is not likely to be much discussion about whether the canoe was an Old Town or a Wenonah. A reasonable person would conclude that the sinking was a human failing, not a problem with the boat.

However, reasonable people can be hard to come by. All of those ridiculous warning labels (I told you my opinions aren't vague) pasted all over ladders are there because of a series of jury awards to people who, for example, stood on the top rung then, duh, fell off. A particularly notorious case involved a farmer who, in the early morning hours, placed one foot of his ladder on a frozen cow patty. When the ascending sun melted the dung, the ladder sank on one side and toppled, bringing the farmer with it. Twelve reasonable people thought the ladder was at fault—or at least that the ladder manufacturer probably had more money than the farmer. But I digress.


The reality is that most sailors rarely stray more than a few miles from home, so the term "seaworthy" takes on an applicable definition.

The reality of sailing is that nearly all of us do it in mostly good weather and within a few miles of our homes. Not surprisingly, this is the target market for the mass producers of sailboats. The design emphasis is on fun at a competitive price. It is wrong, I think, to indict Beneteau, Hunter, and Catalina or any other builder for giving us exactly the boats we want.

In any case, where we are talking about reputable builders, seaworthiness is determined more by design than by manufacturer. Boats that are fun to sail in light air and smooth water—the kind of sailing most of us prefer—are, by design, less suitable for heavy weather. Why? The primary issue is stability.

If the righting moment of a hull is inadequate to resist the wind pressure on the sails, the boat will blow over. This happens to dinghies all the time. In larger boats, we prevent this with ballast. The more ballast and the lower we place it, the less the boat heels. This is good, but too much draft limits where we can sail, and extra weight makes a boat slower in light air. Consequently, most production-built sailboats boast relatively modest draft, and in pursuit of the light-air performance that buyers demand, designers take weight out of these boats. Weight is also sacrificed for economic realities. But a lighter hull won't hold the mast upright when the wind intensifies—unless we make the hull wider. The end result is that the lighter a boat is, the wider and flatter it is likely to be.

"But a lighter weight hull won't hold the mast upright when the wind intensifies."

This is a win-win situation for the way most of us use our boats. Wide beam improves initial stability, meaning the boat heels less. But when conditions deteriorate, wider beam makes the boat more susceptible to capsizing and to remaining inverted. Some wide, shallow boats have a range of positive stability—the heel angle at which they turn turtle—as low as 110 degrees. Of course, the wind can't push the mast below horizontal, but ocean waves can easily roll a boat well beyond 110 degrees. For offshore sailing, any range below 125 degrees is marginal at best—and the higher, the better. A range of positive stability approaching 180 degrees was not unusual for designs from the first half of the twentieth century. Designers calculate this number and the manufacturer should be able to provide it to you for a specific boat.

An alternative numerical evaluation is the CCA Capsize Screening Formula, which offsets beam against displacement. Divide the gross weight of the boat in pounds by 64 (to get the volume of displaced seawater), then divide the cube root of this number into the maximum beam. This formula fails to take other factors into account, most notably ballast, but for comparing boats designed within conventional parameters, it remains a telling indicator. If the result is more than two, this is probably not the best boat to take to sea.


High freeboard and large windows are areas to worry about when considering a long offshore passage.
Making boats lighter, besides leading to excessive beam, tends to make the boat less durable. It can be helpful to think of pounding your way across a wide ocean as participating in a demolition derby. Are you more likely to triumph in a Caddy or a Corvette? Light can be fast and maneuverable (translation: fun) and sufficiently strong for coastal cruising, but when it comes to being pummeled for days on end, four laminates of cloth beats three every time.

High freeboard is often another consequence of wide and flat. When not much hull is in the water, you need more out of the water to get equivalent interior volume. High freeboard raises the center of gravity, but perhaps the more significant seaworthiness implication is that high freeboard impairs windward performance. In strong winds, the windage of the hull overpowers the drive of reduced sails and the boat will only go downwind. An offshore boat must be able to claw to windward and away from a lee shore.

All seamanship texts warn about large windows, and prudent offshore mariners fit oversize portlights with metal, plywood, or thick polycarbonate storm shutters. But what does one do about the great expanses of overhead clear plastic seen on lots of modern production boats? Even if the plastic is thick enough for the task—and I'm not saying it is—what effect do these openings have on the strength of the deck? A wave falling onto the deck of a 38 footer weighs 10 tons per foot depth, never mind that the impact might be at 30 knots or more. In the absence of credible evidence that a builder has beefed up what deck is there to compensate for what isn't there, I would opt for fewer and smaller deck openings.


The potential consequences of flaws in construction increase proportionally with the distance from land.
The potential consequences of shortcomings in a boat's design or construction increase with your distance from land. A weak or vulnerable rudder disqualifies a boat for offshore use no matter who the builder is; likewise, a spindly rig or shoddy construction. For offshore use, I want a hull-to-deck joint that is (at least) bolted together, not screwed. I want the cockpit separated from the interior by a high bridge deck. And I want ample, strong handholds, rounded furniture, and real sea berths.

As a general rule, boats designed specifically for crossing oceans satisfy more of these requirements. (They are also more expensive and less fun to sail on a summer afternoon.) That doesn't mean mass-produced boats can't cross oceans. A number of boats built by the very companies Wayne asks about have successfully circumnavigated, but these same manufacturers—and lots of others—have also built boats that going to sea aboard is about as advisable as standing on the top ladder rung. Come to think of it, maybe a few warning stickers defining unsafe usage for a particular boat wouldn't be a bad idea. Until then, you'll have to make your own evaluation. Do it based on the boat, its design characteristics and construction, and not just the brand name.


Suggested Reading:

Capsize Controversy  by SailNet

The Perfect Cruising Boat  by Don Casey

Criteria for Successful Cruising  by Liza Copeland

 

Buying Guide: Life Rafts

 

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