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Old 10-09-2012, 19:13   #16
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Re: Study Hall: Correcting Weather Helm

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Originally Posted by Chrisgo View Post
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.
If there were no air flow creating lift the center of effort on a sail would be the center of the area of the sail. It has nothing to do with attachment points.

Take a rectangular block of wood (hull). Nail a stick on one end (mast mounted on bow). Nail a sheet of wood to the stick that extends twice the length of the block of wood. ( Hard wing sail attached to the boat only by the mast rigidly held amidships. Half the sail overhangs the stern). Push sideways on the sail approximately at it's middle (CE) which is over the stern of the hull. Assume CLR is the middle of the hull. Which way does it rotate? If it depends on attachment point it will rotate downwind at the bow since it is solely and entirely attached to the boat at the bow. You should find the bow actually rotates into the wind.

John
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Old 10-09-2012, 19:32   #17
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Re: Study Hall: Correcting Weather Helm

Chrisgo, not sure if I have you right, but it makes no difference where attachment points are....ie: attaching a sheet block further forward will not decrease weather helm. Weather helm is a measure of boat hull +sails as a whole. Changing positions of attachments is just changing local stress-loading on the boat and rig UNLESS it changes the position or force of sail ON the hull.
Tightening the backstay may satisfy that "condition"by changing the drive of sail...it's force and maybe the centre of effort too, relative to the hull and other sails but it's not near so obvious a change to make as slacking a sheet, reducing the mainsail size,moving the mast, moving ballast, and so on.
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Old 10-09-2012, 19:33   #18
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Re: Study Hall: Correcting Weather Helm

I come from a windsurf backround, where the legs and feet perform a lot of the attachment points, so I'm still trying to figure this all out. I think my definition of ce is wrong maybe.
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Old 10-09-2012, 19:40   #19
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Re: Study Hall: Correcting Weather Helm

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Originally Posted by Chrisgo View Post
I come from a windsurf backround, where the legs and feet perform a lot of the attachment points, so I'm still trying to figure this all out. I think my definition of ce is wrong maybe.
Nope. It's the same on a windsurfer as a keelboat. The biggest difference is the size of the sails, which translates into more stretch, especially if the sails are made of dacron.

(Of course, when's the last time you saw a windsurfer with dacron sails?)

Weather helm is something any good sailmaker can help you solve with a new suit of sails. The CE can be designed into a sail, and sails can be cut flatter for boats with weather helm issues.

(BTW: With dacron sails, the center of effort can almost always be moved forward by increasing luff tension. This is an adjustment that isn't really effective on sailboards, largely because there's so little stretch in their sails.)
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Old 10-09-2012, 20:02   #20
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Re: Study Hall: Correcting Weather Helm

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Originally Posted by Chrisgo View Post
I come from a windsurf backround, where the legs and feet perform a lot of the attachment points, so I'm still trying to figure this all out. I think my definition of ce is wrong maybe.
OK, let's put you on a Mistral Superlight 260 liter board. We'll make you a lightweight sailor so if you move a couple of feet fore or aft you don't significantly sink the bow or stern. Hold the sail is in the correct fore/aft position to go straight, now don't move the sail relative to the board. Moving your feet from one foot in front of the mast step to one foot behind the mast step will make no difference, you will continue to go straight. In reality it will change, because you will sink the end of the board you're standing on changing the CLR. It is the CE CLR couple that determines helm.

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Old 10-09-2012, 20:05   #21
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Quote:
Originally Posted by s/v Jedi
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,
Nick.
Correct. Sell the big assed aft stateroom boat and buy one with a normal sized transom and length/beam ratio well less than 3.


No substitute for a boat that won't lift the rudder out of the water when it heels. I have had the inclinometer pegged at 45 degrees and still had control of the boat in a puff... Even with roosters tails off of the winches. No rounding up unless I want it to by putting the tiller down to leeward...

Full disclosure, though, boats that don't have excessive weather helm with squirrely rounding up tendency also don't have aft berths with hot tubs underneath.
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Old 10-10-2012, 04:23   #22
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Re: Study Hall: Correcting Weather Helm

Correct me if i am wrong, but is a small amount of weather helm not beneficial, it aids in pointing by having the rudder out a few degrees creating more lift towards the wind.
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Old 10-10-2012, 05:01   #23
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Correct me if i am wrong, but is a small amount of weather helm not beneficial, it aids in pointing by having the rudder out a few degrees creating more lift towards the wind.
Correct. Just not the amount folks are complaining about.
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Old 16-01-2013, 14:36   #24
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Re: Study Hall: Correcting Weather Helm

I believe that the effect quoted of ROLLER furling a headsail has had two outcomes.
1 is that the CE of that sail has now moved forward (and a side effect that if the fairlead was not moved the leech will have opened up some)
2 the boat is now not so powered up, has less heel on so hull distortions are reduced.
Overall outcome is that the weather helm would be reduced, even by default.
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Old 01-08-2013, 03:03   #25
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Re: Study Hall: Correcting Weather Helm

Couples and Forces @ sailtheory.com
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Old 01-08-2013, 05:30   #26
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Re: Study Hall: Correcting Weather Helm

Greetings and welcome aboard the CF, datmbn.
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Old 09-01-2014, 19:47   #27
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Re: Study Hall: Correcting Weather Helm

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Originally Posted by Bash View Post
Nope. It's the same on a windsurfer as a keelboat. The biggest difference is the size of the sails, which translates into more stretch, especially if the sails are made of dacron.

(Of course, when's the last time you saw a windsurfer with dacron sails?)

Weather helm is something any good sailmaker can help you solve with a new suit of sails. The CE can be designed into a sail, and sails can be cut flatter for boats with weather helm issues.

(BTW: With dacron sails, the center of effort can almost always be moved forward by increasing luff tension. This is an adjustment that isn't really effective on sailboards, largely because there's so little stretch in their sails.)
Dacron varies greatly, some Dacron sails will still look fine after 10 years while others won't. It is worth taking a photo of the camber and showing a sail maker before assuming new sails or recutting will solve anything. Recutting is much cheaper and will make the sail maker less money. Dacron does respond to luff tension provided it is cross cut and not radial but it won't get rid of the camber out of the leech if it has stretched.

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Old 09-08-2014, 15:48   #28
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Re: Study Hall: Correcting Weather Helm

Old thread, but always a current topic! Seems like quite a few comments related to racing with luxury of a crew for every sheet. E.G. Tightening backstay. Who does that in a blow! And what do you get for the effort? Not very much improvement compared to trimming or reefing the main.

In my old CCA rule full keeler the optimum way to reduce weather helm is slack the main, then reef at around 18 kts. Second reef goes in around 25 kts. Third above 30kts. This reduces heel and improves weather helm to next to nothing. Rolling in the genoa helps point the boat, but the power comes from the main, hence the most improvement in the original posting about sailing in 20kts of breeze would ideally have been to put in the first reef in the mainsail and maybe slack the reefed main until weather helm disappeared. Anyway, very interesting discussion. Glad it's a sticky at the top of the page.
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