May 26, 2009

Fighting weather helm

WEATHER HELM is not much discussed in polite sailing circles. In the same way that you don’t entertain party guests with tales of an ancestor hanged for treason, or a maiden aunt gone mad from syphilis, you don’t go around telling everybody your boat has weather helm, especially if you’re trying to sell it. Nevertheless, most boats have it, and it’s a vexing thing to have.

Weather helm is the name we give to the tendency of a boat to round up into the wind. The term is actually incorrect, since weather helm is what the helmsman applies in an effort to counteract the tendency to round up, which is known as griping.

If your boat has a tiller, your arm can become mighty tired fighting weather helm. It’s an unrelenting tug that soon becomes much less than fun. Even if you have a wheel, and don’t have to counteract griping with sheer muscle power, excessive weather helm is a bad thing because putting the rudder over in an attempt to keep the boat going straight slows the boat down considerably and puts a heavy strain on the steering gear. In other words, like a leaky loo, weather helm is not a good thing to have.

So what causes it, and, more importantly, how do we cure it? Well, you might have to face the fact that it’s not always possible to cure it entirely, depending on the shape of your hull, the shape, size and position of your keel, and the position of your masts and sails.

What the designer seeks in the first place is a close balance between the center of effort (CE) of the sails and the center of lateral resistance (CLR) of the keel and the underwater hull and appendages.

Normally, the CE is a little forward of the CLR, because (just to make things more difficult) the CLR moves forward as the boat starts to move through the water. So it’s partly a guessing game with a new design. You may have seen boats like the Catalina 30 with little bowsprits added at a later stage. That’s an effort to move the CE forward, to counteract weather helm. But you have to be careful. Move it a little too far forward and you get lee helm, which is even worse than weather helm.

Some designs will always carry more weather helm than others. Hull types like the old IOR designs with a lot of beam carried a good way aft, and hard bilges, will quickly gripe in a puff. Boats with high-aspect-ratio rigs carry weather helm more quickly because the CE of the tall narrow sails is higher, so CE moves farther outboard over the water as the boat heels, thus pushing the boat from the side, and much farther out from the side, gaining leverage with every degree of heel.

Boats with blown-out, baggy sails suffer from weather helm because the CE moves aft. You can cure a bit of that, especially in rising winds, by tightening the halyards and flattening the sail any way you can, which will move the CE forward. The deepest bulge in a sail, the camber, always moves toward the edge under most strain. You can try that yourself with a handkerchief if you need convincing.

What other cures are there? Well, you could move the whole mast and rig forward. (Well, most of us couldn’t, actually, for obvious reasons.) You could rake the mast forward very slightly, or at least set it completely upright if it’s leaning aft. If you have a racing mast, a bendy mast, hauling on the backstay will induce an aft bend in the mast that will flatten the sail and reduce weather helm. In heavy winds you should set the mainsail traveler down to leeward as far as possible so that the sail spills wind and lies flatter. That helps quite a lot.

One thing often overlooked is that a large headsail can contribute to weather helm, too. Quite a lot of the area of your 150 percent genoa lies aft of the CLR, which is somewhere in the middle (in fore-and-aft terms) of your keel. You might as well be adding that extra genoa area to your mainsail. Change down to a smaller genoa or working jib, or roll it up to a similar size, and your CE will move forward.

And let’s not forget the best cure of all: reef the mainsail. Get rid of the sail area at the aft end of the boat that is constantly pushing the stern away from the wind and making the boat want to point up.

A little weather helm is a good thing. You don’t want it to disappear completely. You just need to be able to control it. Tank testing has shown that about 2 or 3 degrees of rudder from dead center helps lift a sailboat to windward. More than 4 degrees just acts as a brake to your progress.

In gusty weather, most of us will try to ride out the puffs by easing the mainsheet and putting the rudder over to leeward, but because excessive heeling is a major cause of weather helm it’s always wiser to reef down and keep the boat more upright if the wind is likely to continue at a greater strength.

Do what you can to lessen weather helm. It’s a good feeling to be in decent control of your boat in heavy wind. And I’ll tell you what — I won’t mention your weather helm to anyone if you don’t mention my maiden aunt.

Today’s Thought
It would have been as though he were in a boat of stone with masts of steel, sails of lead, ropes of iron, the devil at the helm, the wrath of God for a breeze, and hell for his destination.
—Emory A. Storrs

“The doctor said I’d be on my feet in two weeks.”
“Was he right?”
“Yeah, I had to sell my car yesterday.”


Jennifer Moran said...

John, hello!
I think your excellent quote should be attributed to Emory Storrs rather than Stones. I copied the same quote once from The New York Times archive. It was said of President Andrew Johnson in the mid-1860s.
Thank you for the blog. It's great reading - as always, instructive and interesting.

John Vigor said...

Jennifer, how clever of you. Yes, I'm ashamed to say I read it wrongly in Stevenson's. That quotation should indeed have been attributed to Emory Storrs, not Stones. Thank you for putting the record straight.

Incidentally, I knew a Jennifer Moran once many years ago, in Durban. Are you that one, or another?