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Old 04-02-2008, 11:33   #1
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Study Hall: Correcting Weather Helm

An excellent note on Weather helm authored by GordMay
Quote:
Poor balance (Weather Helm) increases as the “Centre of Effort” moves aft of the “Centre of Lateral Resistance”, and can also be caused by warped rudders, skegs, and keels/centerboards, or even by baggy sails.

Sail trim to move the C of E forward, and reduce weather helm:

Remove mast rake (or even rake slightly forward).

Reduce wind pressure on the main, or increase the pressure on the head sail. This can be done by shaping (trimming) the sails, and dropping the main to leeward. As the wind increases, shape/position become more critical (should be flatter). If you can, tighten the backstay. This helps to pull the fullness out of the main and will flatten the head sail. The idea is to flatten the sails and keep the draft forward.

Tighten the outhaul to flatten the bottom part of the main. At the same time tighten the Main and Genoa halyard to keep the draft(s) forward. Bottom batten should line up with boom, top batten with masthead. Twist at the top of the mainsail will allow wind to spill.

Move the Genoa lead aft to flatten the lower section and twist off the leech.

Dropping the boom to leeward after shaping will reduce weather helm.

Add a boom vang (helps maintain shape when easing out).

More weight aft and windward, less weight in the bow (move anchor, empty the water tank in bow)

Reef (the main more than the jib).
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Old 04-02-2008, 12:13   #2
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Other ways to reduce weather helm include:

1) Have main recut to a battenless and hollow leech shape.

2) Add a fixed outboard keel extension to the stern.
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Old 04-02-2008, 12:53   #3
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Thanks for the great information. My first charter was last September and our local SoCal weather threw a few twists at me. The wind was about 10 knots when I departed and blew up to about 22 knots. I was not familiar with the reefing lines on the mainsail of this particular Catalina 30 and I wasn't excited about having crew up on the foredeck with the boat heeling quite a bit, the wind, and some moderate swell. My crew was one able bodied, knowledgable sailor and a newbie with a hangover.

The experienced sailor suggested rolling the jib in about 20% and I agreed. He did that and it solved our weather helm problem. My redicence at having crew on the foredeck under the circumstances is an indication that the decision to reef was made a little late. Still, our weather helm was corrected and it was a valuable learning experience, but aren't they all?
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Old 23-08-2009, 10:21   #4
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Quote:
Originally Posted by Viking Sailor View Post
Other ways to reduce weather helm include:

1) Have main recut to a battenless and hollow leech shape.

2) Add a fixed outboard keel extension to the stern.
Unless the boat was poorly designed I wouldn't do either of these. And if it was that poorly designed I'd sell it and make it someone else's problem.

If you have a Dacron main with several seasons of use it has likely stretched and the draft has shifted aft. If rig tune and other issues have been addressed then a new main corrects the problem. Also the boat heels less since the new sail can be trimmed flatter. And it points better.
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Old 23-08-2009, 14:30   #5
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Weather helm comes from more sources than mentioned in the above quote. Often it comes from the boat heeling to the wind - thus making the underbody shape of the heeled hull assymetrical AND moving the center of sail outboard to the lee side which result's in the boat's tendency to come round.

So, in a well designed and trimmed boat reducing the heel reduces the weather helm.

I believe that in a cruising boat the 'design' factor is of utmost importance and some designers simply never got it right. My boat - a modified underbody long keeler with tiller steering - develops no weather helm no matter how hard I push her. The only time I get some amount of it is if I do something crazy like trying to beat under full mainsail in 25 knots of wind.

b.
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Old 23-08-2009, 21:28   #6
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I agree fully with Barnakiel. The changing shape of the under water part of the hull when heeling is the factor for weather helm when it increases in gusts (= more heel).

Think about it: to move the bow off the wind you would want more pressure on the jib. But if you do the opposite, furl it a bit, weather helm decreases. This is because you heel less.

Same for the main. When you put in a reef, or flatten the sail, you de-power it, resulting in less heel.

So I really do not agree with Gord's point to "increase the pressure on the head sail". All effort should be to reduce heeling so reefing, flattening sails (if the main is baggy you can still flatten it by reefing), bending mast more if you have the luxury of backstay adjuster, tighten vang and sheets and let traveler out a bit.

"Narrow" boats with balanced lines don't have the problem up to some point of heel.

cheers,
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Old 18-02-2010, 14:08   #7
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Many boats develop weather helm because the owners wait too long to replace their mainsail. The draft gets deeper and moves aft. In many cases people think they have a problem with the design of the boat or the rig tuning and the culprit is an old sail.

Going battenless will not necessarily fix the problem and will accelerate the demise of the sail. It's generally best not to throw a bunch of money into old tired sails. Most lofts love seeing you do it though because there is often more money to be made in repairs than selling new sails.
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Old 12-10-2011, 23:03   #8
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Re: Study Hall: Correcting Weather Helm

There seems a point of discussion regarding GordyMay's comment to place more pressure forward of the CLR (Jib). I think he described how to accomplish it clearly enough, the point is that balance of the boat needs to change. And, if i am correct, in no circumstance do you want less force up forward

I have a ketch that has a mighty strong weather helm and i have been working lately to correct it and learning alot. Time on the water and enough wind to put all the aformentioned measures to practice will ultimately provide me with the right boat balance.

One I havent given thought to is the way a sail curls along the leech. Will this cause weather helm? I am sure that proper trim can correct this.
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Old 13-10-2011, 14:21   #9
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Re: Study Hall: Correcting Weather Helm

Borealis,

With some boats, excessive weather helm is a design issue and while it can be reduced, it's always going to be an issue. I am not suggesting that's the case with your boat, but simply mentioning it as a possibility. If it was an amateur constructed boat you may want to research the mast's position to see if it matches the designer drawing. Of course designer's don't always get it right either. That was an issue on some of the Tayana 37's. Check to see if the boom lengths are correct.

The cupping of the leech probably isn't making a huge difference but feel free to send me a picture for review. My sail designer and I can have a look.

If the sails are older, that is quite frequently the culprit as I explained in the previous post previous to yours.
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Old 13-10-2011, 14:40   #10
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Re: Study Hall: Correcting Weather Helm

Hold that thought while I go get a fork. This can of worms looks like it might be tasty.
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Old 13-10-2011, 14:56   #11
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Re: Study Hall: Correcting Weather Helm

And one more my sail maker mentioned to me..

A shrunk mainsail bolt rope.
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Old 13-10-2011, 14:58   #12
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Re: Study Hall: Correcting Weather Helm

So, what's the deal when the weather helm is only noticeable on one tack?
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Old 13-10-2011, 15:36   #13
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Re: Study Hall: Correcting Weather Helm

The boat is heavier on one side than on the other.
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Old 14-10-2011, 08:16   #14
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Re: Study Hall: Correcting Weather Helm

Next time you're sailing and noticing weather helm, try to reduce the jib size by furling it in 1/3 to 1/2. This is exactly opposite of what is being suggested here but I bet many will see reduced weather helm with reduced jib size.

I do not state that reducing pressure of the forward triangle directly leads to reduced weather helm... it's an indirect effect;

For most boats, weather helm is just caused by asymmetric submerged hull shape. This is caused by heeling. Reduce heel angle and you reduce weather helm.

Long & narrow boats (like me :-) do not have this issue and only then you find that tuning sail-balance makes a difference even when heel angle is the same.

ciao!
Nick.
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Old 10-09-2012, 18:51   #15
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Re: Study Hall: Correcting Weather Helm

I know this is an old thread. Really, I know, but I have to agree with Jedi.

I am looking at a modern 32' production cruiser that some say has weather helm issues, so this topic interests me.

Also I think people misplace there center of effort points. Is it not so much where the clew or end of the sail is, but where the mainsheet or traveler is attached to the boat?

I have heard of tightening the backstay to bring the c of e aft, but again, the pressure, (attachment points if you will), are still in the same place, on not sure why that would work.
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