Losing control at sea

IT’S A GREAT PITY that human beings are unable to pass on their lifetimes of learning to future generations. Nature has not provided us with the shortcuts she gives to other forms of life, such as birds, which do not have to learn to peck their way out of an egg or how to build a nest. For them, the knowledge is built in. But humans have to learn practically everything over again from scratch, so the accumulated knowledge of people like Einstein is not available to be built on immediately and taken to the next step.   

I mention this because there are always neophyte sailors who are anxious not to kill themselves at sea. This means that as new generations come along they have to learn the same old things all over again.

This is why, every few years, I find people asking me the same old questions, such as “Why do I lose control of the boat when we’re running before the wind in large waves?”

Well, once again let me say that interesting things happen at sea. Your boat loses stability in broken water, for a start. But do you know why boats so often broach, roll broadside on, and capsize when they’re running before the wind in large waves? It’s because when a wave breaks under your stern you have practically no steering power to keep her running straight. The rudder is suspended in foam, not water, and it can’t do its job. If you’ve ever been dumped by a big breaker while body surfing you’ll know the feeling of not being able to float high enough to get your head above water.

And if your boat heels to 45 degrees, you don’t have much steering ability, either. Think about it. The rudder is trying to lift the stern toward the sky as much as it is trying to turn the boat sideways. And, of course, if you do a 90-degree capsize you can’t steer at all. If the rudder isn’t totally out of the water, as it would be on a tubby light-displacement boat, it will be horizontal and unable to turn the stern either way.

Stability at sea is always a fascinating subject for sailors, whether they actually get away from the sight of land or not, and one of the very basic facts about boats is that stability comes as a cube of the length, other things being more or less equal. This means that a 30-footer is 72 percent more stable than a 25-footer, which explains why a 30-footer can stand up to its canvas so much better. It also explains why a 30-footer costs so much more than a 25-footer. But that’s another subject Some other day, perhaps.

Today’s Thought
It hath been an opinion that the French are wiser than they seem, and the Spaniards seem wiser than they are; but howsoever it be between nations, certainly it is so between man and man.

—Bacon, Essays

Tailpiece
Golfer: “You must be the worst caddie in the world.”

Caddie: “Oh come now — that would be far too much of a coincidence.”

(Drop by every Monday, Wednesday, Friday for another  Mainly about Boats column.)

Watch out for the crest

I SUPPOSE it’s pretty natural for sailors to ask themselves just how seaworthy their boats are, compared with others. One thing they worry about in this connection is stability, but I wonder how many of them know the difference between static and dynamic stability.

In other words, I wonder if they know the difference between how stable their boats might be (that is, how resistant to capsize) in calm water (static) and how unstable they might be at sea in big waves (dynamic).

It’s an established fact that no amount of static testing will reveal how much more vulnerable a boat is to capsize when it is weaving its way through heavy swells.

This phenomenon was investigated in the late 1800s by William Froude, an eminent British naval engineer who was well versed in fluid dynamics. Froude did many experiments for the British navy, including his most famous, which determined the amount of force that water exerts on a body passing through it. But the experiment that should concern all small-boat sailors dealt with the tendency of a sailboat to capsize on the crest of a wave.

As you have probably noticed, you get a strange feeling in the pit of your stomach when your boat heaves upward suddenly on the face of a steep wave and then drops off suddenly. Froude discovered that at the top of the heave your boat experiences a degree of weightlessness.

At that stage, the boat is virtually in free fall. And thus, Froude found, a boat’s stability momentarily vanishes completely as she floats over the crest. At that moment there is no resistance from the water to stop her from being blown over by the wind.

This rather scary theory is well borne out in practice. The phenomenon of ocean-going sailboats and small racing dinghies capsizing on the crests of waves, even non-breaking waves, is well documented. The degree of danger depends, among other things, on the height and steepness of the swells as well as the design of your boat.

Froude also found that the presence of a wave crest near amidships resulted in a decreased righting moment. On the other hand, a wave trough amidships increased the righting moment, compared with the static stability.

If this all seems highly scientific to you, be aware that good sailors know intuitively that when they’re running in heavy seas in a displacement hull they shouldn’t spend too much time on the crest of a wave. That’s why they try to slow the boat with a drogue, to let the wave crest pass underneath quickly. Alternatively, they try to aim the boat off 20 degrees or so to one side or the other, to avoid surfing dead downwind, and to get the rudder out of the foam, where it can’t work properly. Sitting on top of a wave, especially a breaking wave, is never where you want to be.

Today’s Thought

The sea thinks for me as I listen and ponder; the sea thinks, and every boom of the wave repeats my prayer.

— Richard Jefferies, The Story of My Heart

Tailpiece

“I see that restaurant on Main Street is hiring a gypsy band from Romania, and waiters dressed as bandits.”

“That’ll make a nice change. Last time I was there they had bandits dressed as waiters.”

(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)

Try to stay off wave tops

I RATHER DOUBT that many people choose stability as their main reason for buying a certain boat. We all like our boats to be stable, I’m sure, but the thing that makes us buy a boat is more likely to be speed, seaworthiness, accommodation, or sheer beauty. The fact is, most of us don’t know very much about stability. For example,  I wonder sometimes how many sailboat owners understand the difference between the two most important kinds of stability, static and dynamic.

In other words, I wonder if we know the difference between how stable a boat might be in calm water (static stability) and how unstable it might be at sea in big waves (dynamic stability).
It’s an established fact that no amount of static testing will reveal how much more vulnerable a boat is to capsize when it is weaving its way through heavy swells.
This phenomenon was investigated in the late 1800s by William Froude, an eminent British naval engineer who was well versed in fluid dynamics. Froude did many experiments for the British navy, including his most famous, which determined the amount of force that water exerts on a body passing through it. But the experiment that should concern all small-boat sailors dealt with the inclination of a sailboat to capsize on the crest of a wave.
As you have probably noticed, you get a strange feeling in the pit of your stomach when your boat heaves upward suddenly on the face of a steep wave and then drops off suddenly. Froude discovered that at the top of the heave your boat experiences a large degree of weightlessness.
At that stage, the boat is virtually in free fall. And thus, Froude found, a boat’s stability vanishes completely as she floats over the crest. There is no support from from surrounding water to stop her from being blown over by the wind.
This rather scary theory is well borne out in practice. The phenomenon of small racing dinghies capsizing on the crests of waves is well documented. Ocean-going racers do it, too. The degree of danger depends, among other things, on the height and steepness of the swells as well as the design of your boat.
Froude also found that the presence of a wave crest near amidships resulted in a decreased righting moment. On the other hand, a wave trough amidships increased the righting moment, compared with the static stability.
If this all seems highly scientific to you, be aware that good sailors know intuitively that when they’re running in heavy seas in a displacement hull they shouldn’t spend too much time on the crest of a wave. That’s why they try to slow the boat with a drogue, to let the wave crest pass underneath quickly. Sitting on top of a wave, especially a breaking wave, is never where you want to be.
Today’s Thought The sea thinks for me as I listen and ponder; the sea thinks, and every boom of the wave repeats my prayer. — Richard Jefferies, The Story of My Heart
Tailpiece “I see that restaurant on Main Street is hiring a gypsy band and the waiters are dressed as bandits.” “That’ll make a nice change. Last time I was there they had bandits dressed as waiters.”

(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)

Narrow boats are safer boats

EVERY NOW AND THEN, someone who has become imbued with the idea of going cruising asks me: “Isn’t a wide boat safer than a narrow one?”

The answer is “Not necessarily,” but it’s difficult to explain this to a newbie, who, just by looking at it, must justifiably conclude that a wide hull is more difficult to capsize than a narrow one.

Furthermore, a wide hull offers a lot more accommodation down below for the same overall length, which is something the yacht brokers like to emphasize.  Without stretching the truth too far, they can also tell a prospective buyer that a wide boat has tremendous stability.

But that’s only part of the truth. A boat that is excessively wide has a wonderful amount of initial stability, certainly, but what an ocean-going cruiser has to consider is ultimate stability — the ability of a boat to right itself after having been knocked upside down by a breaking wave.

The point is that a very wide boat is perfectly happy to stay upside down; and while it’s inverted water may pour in everywhere — perhaps enough to sink it in a short time.

The narrower the hull, everything else being equal, the quicker and more surely a boat will right itself from complete inversion. It’s very unstable when it’s upside down, Of course, if you’re looking around for a boat capable of crossing an ocean, the yacht broker is not likely to introduce the subject of capsize in extreme conditions. But that’s precisely what every would-be cruiser should plan around.

Everything on deck and down below should be designed and built with a 180-degree knock-down in mind. The chances of it happening to you are, admittedly, remote. But if it does happen, and you planned for it, the chances of your surviving are increased immeasurably.

Today’s Thought

He that will not sail till all dangers are over must never put to sea.
— Thomas Fuller

Tailpiece

“Help, there’s a creature destroying my garden. I think it escaped from the zoo.”
“Try to keep calm, madam.  Can you describe the animal?”
“Well, it’s big and gray, with large ears. It keeps picking my cabbages with its huge tail — and I can’t tell you where it’s putting them.”

 

(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)

When is a boat too tender?

MOST SAILBOATS lacking in initial (or form) stability lose their tenderness as they heel and become progressively (and reassuringly) stiff. But if a boat fails to start resisting heeling after she has reached an angle of 15 degrees or so, and continues simply to lie over and dip her gunwale in reasonably moderate winds, she’s probably too tender for safety. If she won’t stand up to all working canvas in 15 knots or so, don’t hesitate: seek professional help, preferably from a naval architect.

One of the paradoxes of boat design is that the boat that seems to be tender initially will likely be more seaworthy than the one that is stiff to start with. That’s because most capsizes are caused by wave action, not wind, and when a boat is upside down she will recover more quickly if she is reasonably narrow and has a deep, heavy, ballast keel. A wide shallow boat, while stiff to start with, tends to remain upside down a long time if she is capsized by a wave.

Liveaboard cruising boats often lose stability imperceptibly as their owners gather possessions over the years. This causes a boat’s ballast keel to become an ever-smaller percentage of displacement.

The situation can be improved substantially by lowering weights wherever possible. These include internal ballast, books, water and fuel tanks, batteries, outboard engines clamped to the aft rail, life rafts, dinghies, provisions, and anything higher than the boat’s center of buoyancy.

Keep your spars and rigging wire as light as possible. That goes for the sails and fittings, too. Hanked-on foresails improve stability more than roller-furling sails because they can be lowered in bad weather.

Incidentally, it pays to lessen weight aloft. Because of the effect of leverage, every ounce off the top of the mast is worth a pound added to the keel.

Today’s Thought

Remember that there is nothing stable in human affairs ...
— Isocrates, Ad Demonicum

Tailpiece

Some of us believe a girl’s family tree doesn’t matter, as long as she has the right kind of limbs.

(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)

Disappointment and stability

ANOTHER State of the Nation speech. Another evening of disappointment. No tax breaks for sailboat owners. No bailout for those behind with their marina fees. No $8,000 discount for buyers of new boats. Sheesh.

I turn to my inbox for consolation. A message from Sam Psmythe (silent P as in bath) says:

“I saw your piece about how sailboats capsize more easily on the crest of a wave. Well, duh. Surely everybody knows that. What other banalities masquerading as gems of wisdom are you going to parade for us?”

Well, just between you and me, old Sam is pretty nifty with words, but he’s a bit of a know-all. I think he has forgotten that new generations keep coming along, generations that have to learn all the same old things all over again, because humans don’t seem to be able to pass on the seeds of experience to the fruit of their loins.

So while Sam may think he’s heard it all before, I cater to the newbies, the neophytes who are anxious to learn how not to kill themselves at sea. And interesting things happen at sea, believe me. Your boat loses stability in broken water, for a start. Yes, we’ve been there, done that. Thanks, Sam.

But do you know why boats so often broach, roll broadside on, and capsize when they’re running before the wind in large waves? It’s because when a wave breaks under your stern you have practically no steering power to keep her running straight. The rudder is suspended in foam, not water, and it can’t do its job. If you’ve ever been dumped by a big breaker while body surfing you’ll know the feeling of not being able to float high enough to get your head above water.

And if your boat heels to 45 degrees, you don’t have much steering ability, either. Think about it. The rudder is trying to lift the stern toward the sky as much as it is trying to turn the boat sideways. And, of course, if you do a 90-degree capsize you can’t steer at all. If the rudder isn’t totally out of the water, as it would be on a tubby light-displacement boat, it will be horizontal and unable to turn the stern either way.

Stability at sea is always a fascinating subject for sailors, whether they actually get away from the sight of land or not, and one of the very basic facts about boats is that stability comes as a cube of the length, other things being more or less equal. This means that a 30-footer is 72 percent more stable than a 25-footer, which explains why a 30-footer can stand up to its canvas so much better. It also explains why a 30-footer costs so much more than a 25-footer. But that’s another subject for Sam to get enraged about. Some other day, perhaps.

Today’s Thought
It hath been an opinion that the French are wiser than they seem, and the Spaniards seem wiser than they are; but howsoever it be between nations, certainly it is so between man and man.
—Bacon, Essays

Boaters’ Rules of Thumb #7
Statistics from cruiser in Mexico, the Caribbean, and the South Pacific show that the average yacht spends 10 percent of the time at sea, 5 percent tied to docks, and 85 percent at anchor. This emphasizes the importance of good and easily handled ground tackle, and an efficient dinghy.

Tailpiece
Golfer: “You must be the worst caddie in the world.”
Caddie: “Oh come now — that would be far too much of a coincidence.”