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Date Posted: - Wednesday - 09/17/08 - 4:21pm
Author: matts
Subject: weather helm on a ketch

I'm finishing up a piece on ketch rigs for "Sailing"

I know that a mizzen shoves the stern around, hence the weather helm, and the raked masts also increase weather helm; and a main, mizzen, and jib will balance nicely in a light wind; hence, BUT, given a 180 Genoa, wouldn't the CE move forward (especially since a jib is typically the power sail and most efficient on any boat) if it were hoisted, especially on a brisk day.

Personal experience says "no"--my 180 on a brisk day (shouldn't have it up anyway) is a guarantee of a weather helm.

What's going on?

matts

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Replies:

[> It's fate! :) -- Randall, Murre, M31, - Wednesday - 09/17/08 - 11:17pm

Interesting question, Matts. If I were a guessing man (who’s been noodling this most of the evening now), I might say the following:

1. Kind of like the idea of hull speed, Center of Effort is a theory with practical applications rather than being an immutable rule. Once the boat is out on the wind and the water, all hell breaks loose, and a host of other factors come into play.

2. Sure, flying a jib and main moves the CE forward of where it was when the main was flown alone, but that’s not a guarantee of no weather helm, only a reduction in weather helm (usually). I’ve never noticed that Murre goes wandering off to leeward when I fly just the jib, and this is probably because most boats are designed with a little weather helm in mind. But if I’m in a stiff blow with main and jib up and fighting the wheel, I will fight it less if I drop the main.

3. And / or it could be you are simply experiencing the effects of healing, which itself creates weather helm. Reacting to the force of the wind, the boat heals, pushing the CE out over the water. Wind force on the sails is forward, but if the force is at the CE, it pivots at the hull; thus wind force tends to rotate the boat into the wind when the boat is heeled … requiring weather helm to correct it. The more wind, the more heal, the more helm. And if you’re flying a 180 into a brisk breeze, it’s probably quickly overpowered.

4. I’ve also read that a bow wave can push the bow to windward. If you’re close hauled and hauling ass, your wave alone will create some weather helm.

5. Another factor could be how your sails are trimmed. I’m sure you’ve seen those sailors who pull the main in dead amidships when close hauled. If the boat is a Mariner and the jib an old one, it’s probably not possible to hoik it in as flat as the main; thus there’s more power in the main than the jib and … thus … weather helm.

Bottom line: if it’s a sail boat, it’s gonna have weather helm. It’s fate.

:)

RR


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[> Jib and Jigger -- Gitano, - Thursday - 09/18/08 - 3:05pm

I agree with Randall. It blows strong here on the SF Bay, and the Ketch rig allows the option of being able to drop the main and sail under the jib and mizzen only. This allows the boat to right herself, sail along on her bottom, and cruise with no noticable weather helm. Its quite pleasureable, really.


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[> [> A difference -- Chuck, - Thursday - 09/18/08 - 11:37pm

There is a difference between weather helm and the boat simply being overpowered because there is too much sail up for the conditions. Sometimes it is hard to tell the difference.


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