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Re: Cockpit placement & weathercocking
By:Nolan Penney
Date: 9/17/1998, 8:21 am
In Response To: Re: Cockpit placement & weathercocking (Tom Scheibe)

Leehelm vs weatherhelm. A boat with weather helm will turn into the wind, a boat with leehelm will turn away from the wind.

In very loose kayak terms, a boat with leehelm is one that with you in the middle, having a huge bow sticking up into the wind, would turn away from the wind and try to run *with* the wind or storm. Not good, because you normally want your bow into the wind and waves to ride out a storm.

A kayak with weatherhelm would probably have you further forward, a lower bow, a higher stern. This boat when in the wind would turn *into* the wind. This is good for riding out storms. But too strong a weatherhelm and you couldn't escape to run from it because you couldn't turn the boat.

Hull shapes contribution is part of the center of effort in the water, not the air, and is independent of the center of gravity. Lets assume you've got a kayak with a tall bow. Now that should catch air and make the boat prone turning away from the wind (leehelm). But, lets also assume that you decided to stick a great big keel or daggarboard on it, up near the front. Now the boat is going to try to pivot around that daggarboard instead of the center of gravity. So you've got the largish bow catching air, but having a short distance to the daggarboard. The stern, with a smaller air catching area has a very long lever arm to the daggarboard though creating a powerfull turning force, and may be stronger then the bows turning force in fact. So in this case, the boat will turn into the wind because of that daggarboard placement. That's pretty much how a sailboat, with all that sail area in the middle and up front, still turns into the wind. As in why you don't see daggarboards at the back of the boat.

The problem is significant for sailboats. For the obvious reason of their sails. As a general rule of thumb, you want a sailboat with a little bit of weatherhelm. But not so much you have to fight the boat to turn and run. Or worse, are unable to turn and run. In paddling kayaks, it's more a fatigue factor, in that you have to keep making paddling corrections. It would be very difficult to find or even make a kayak that had what could be called severe problems with this, imo.

Nick would be very good one to talk to about this effect with kayaks, because his designs present a comparatively large sail area fore and aft. I'm not knocking his design. Presenting a large bow is very important for riding over waves instead of finding yourself under them. Similarly the stern for running with waves instead of getting knocked down by them. But in doing this, you do present a larger area to the wind. So he should have a good bit of experience with how significant in his opinion wind cocking really is for sea kayaking. I'd be interested in your input Nick.

> Ok... So perhaps I don't understand the terms leehelm and weatherhelm. To
> simplify, given: a boat is symmetrical and whatever the rocker is, is
> symmetrical from the center of mass, and the trim is balanced evenly
> between the center of mass, then will a beam wind blowing from east to
> west blow the boat evenly toward the west? If the center of mass is aft of
> the center of the boat, which way will the bow turn? east, or west? And
> given that the center of mass is forward of the center of the boat, which
> way will the bow turn? Doesn't it follow if the bow turns into the force
> of the wind (east)the forces (wind) acting on the boat are either stronger
> on the stern, pushing it more to the west, or less on the bow, in essence
> producing the same effect? As I understand it, weathercocking means the
> bow turns toward the direction from which the wind is coming.

> Something isn't making sense to me. Maybe I'll go back to just one bottle
> of Pinot for lunch. thanks again, Tom

Messages In This Thread

Cockpit placement & weathercocking
Tom Scheibe -- 9/15/1998, 3:53 pm
Seat-of-the-pants approach and a double decker
Paul Jacobson -- 9/18/1998, 2:54 am
Re: Cockpit placement & weathercocking
Mike Scarborough -- 9/17/1998, 8:22 am
Re: Cockpit placement & weathercocking
Nolan Penney -- 9/16/1998, 8:58 am
Re: Cockpit placement & weathercocking
Tom Scheibe -- 9/16/1998, 8:48 pm
Re: Cockpit placement & weathercocking
Nolan Penney -- 9/17/1998, 8:21 am
Re: Cockpit placement & weathercocking
Jerry Weinraub -- 9/16/1998, 6:55 am