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Old 26-12-2007, 04:45   #1
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weather helm, help !

a pal of mine is about to move his mast forward to reduce weather helm ! a drastic step, i think . can we have some of the wide knowledge look at it on this forum ,please ? the yacht is 38 ft timber traditional long keel mono with a tall ,cutter rig . big gennyand jib .the weather helm has been getting worse over the last few years and its becoming a fight with a high rudder angle producing lots of drag .he feels that she will sail faster without this drag and is considering a mast move ,forward of 300/400mm . a fair amount of work !. the sails are old / 15 years ,perhaps. there is very slight aft rake on the mast. , would a baggy main produce this severe weather helm?
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Old 26-12-2007, 05:07   #2
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A baggy main will definitely produce weather helm. So will a baggy genoa. Trying new or recut sails before taking such drastic action as moving the mast would seem prudent to me.
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Old 26-12-2007, 05:11   #3
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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 26-12-2007, 07:04   #4
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Well done Gord - a comprehensive, concise and accurate response. And lets face it, if the weather-helm has increased over the years it is decidedly not because the position of the mast has changed!

Brad
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Old 26-12-2007, 11:46   #5
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I agree..your response is great...I've seen many other write ups on correcting weather helm but yours is simple and clear...could a category be added to FAQ for things like this. The question could simply be "How do I correct weather helm?" and the text is simply your response
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Old 26-12-2007, 12:16   #6
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Spot on Gord.

I would certainly remove the rake in the mast as the 1st, most logical and easiest step. That may make a considerable difference. The deterioration over time, suggest a "Wear" problem which would suggest that the baggy sail could be the culprate. There is nothing like replacing a worn out mainsail to improve deteriorating performance.

If the boat performed well at one time with the mast where it is, it makes little sence to reposition the mast. That could merely introduce new problems.

You might also look at weight distribution in the boat (as Gord mentioned).
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Old 26-12-2007, 14:07   #7
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Quote:
a pal of mine is about to move his mast forward to reduce weather helm ! a drastic step, i think . can we have some of the wide knowledge look at it on this forum ,please ?
There are probably a long list of things that won't work. This would be near the top. I think the ideas about sails above are more likely to be the solution. Gord as always adds some serious information as well.

Healing a boat over too far can also load the rudder up and give the impression of weather helm (it feels the same). Boats with large skeg hung barn door rudders can get that (I've had 2). You flatten them out and the rudder handles just fine. Often speed increases too.

This just points out a good rule of thumb: When you think you know more than the guy that designed the boat it's probaly a really bad idea.

As an alternative to moving the mast try shortening the boat.
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Old 26-12-2007, 14:50   #8
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When I bought my boat we had acute weather helm. Acute in that removing your hands from the helm resulted in an immediate hard windward turn. The boat sails perfectly balanced now.

I made two rigging adjustments. The first was removing mast rake. The second was tightening the forestay to remove what was a considerable amount of headstay sag.

I'm adding my comments because I sail with baggy sails. In my case, it's not a contributing factor.
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Old 26-12-2007, 15:17   #9
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I agree with all of the above.
If the weather helm is getting progressively worse, it sure can't be the mast gradually moving out of position!

Steve B.
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Old 26-12-2007, 17:49   #10
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How interesting. Last night we sailed a couple of hours. We spent most of the time sailing with hands off the tiller to investigate and understand better the different sail trims.

Your friend might consider applying Gord's advice remembering the biggest difference is main vs. genny sheeting. We also learned a tremendous amount about sail shaping last week when we borrowed a friends Mumm 30. A high performance boat shows the effects of sail shape (cunningham, boom vang, outhaul, backstay and barberhauler contriols) more readily than a big heavy cruiser.

A couple of hours practicing hands off rudder in a steady breeze is a great way to understand your boat and weather helm.
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Old 26-12-2007, 21:24   #11
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It also helps to have a clean bottom. I don't think that was mentioned. Forgive me if it was.
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Old 27-12-2007, 05:21   #12
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Lightbulb weather helm "forum "

thanks everyone , especially Gord, its great to have this source of help , i will enjoy the coming chat with the skipper , on his return next week and show him the value of this forum , gramos
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Old 27-12-2007, 05:44   #13
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I agree with you Paul, although I suppose it is real weather helm you are feeling if the boat wants to round up with excessive heeling. This isn't just a phenomenon with skeg rudders but is equally applicable to any rudder design. As the boat heels she is sailing off her lines, the leeward topsides effectively becoming part of the boats underbody. This generally accentuates the fore/aft curvature and the boat wants to follow the curve of the leeward side up to windward. In addition, as you mention, the rudder has now tilted off a verticle plane and not only has less bite, but the flow of water over it is split between side to side and up and down directionality.

Simply put - sailing flatter reduces weather helm and increases speed. Much of Gord's advice re: sail trim accomplishes this as well as moving the center of effort forward.

Brad
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Old 04-02-2008, 08:54   #14
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I am gramos's friend with weatherhelm problems. firstly thanks all for your replies .the boat has had helm problems since I bought it [not progressive]and in spite of much sail tweaking over 2 atlantic passages without huge improvement leading me to try something more radical. The boat is a home design and home built by the previous owner. Even though she is well built I still feel the mast position is too far aft and as I have a trip from Greece to the Virgin Islands planned for this August I feel I must take this oppotunity to tackle this problem for once and all. On previous crossings I would be continually reefing to keep my aries in control thus losing valuable boat speed. Any further comments from the readers would be most welcome.
Cheers Malcolm Campbell
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Old 04-02-2008, 09:50   #15
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The boat is a home design and home built by the previous owner. Even though she is well built I still feel the mast position is too far aft
You really need to consult a naval Architect given it's a home built boat and may not have been built correctly. Were it not a home built boat I would strongly suggest it is probably something else. Moving the mast is a serious bit of surgery and you don't really want to repeat the operation. It should be the right fix done correctly.

It may be best to try and validate the original design if you can find the original plans. It needs to be an engineered solution and not a guess of how far it's off - even if it really is wrong.
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