Weather Helm

Submitted by Scott Mauney on Fri, 12/03/2010 - 00:28
Now that Natalie and I have semi-retired from racing I thought I would share something that came to light only towards the end of our racing days. What is the greatest source of weather helm on a Flying Scot? 1 Rudder Angle, 2 Too Much Heal, 3 Sail Trim, 4 Other? The answer 4 Other. It's the point of attachment for the main-sheet strap on the rudder head. The main-sheet, at this attachment point, is pulling the front of the rudder head away to leeward inducing weather helm. If you move the strap 1&1/4" aft, then you will take away most of the weather helm. 2" back will make the helm go neutral, and 3" back will give lee helm – assuming our rudder rake position. Many FS sailors sail with the rudder straight down. This may give a false sense of easing pressure on the blade, but will actually facilitate snapping the blade at the turning point underneath the rudder head. Try moving the strap an 1&1/4" back, and sail with some rake in the rudder blade. We sailed the rudder blade 2 to 3 inches back measured from the front of the rudder head down parallel to the tip and then 2&3/4" back. If you move the main-sheet strap 1&1/4" back - the factory rudder rake will feel great. Many young sailors, who jump into the class, often complain about the excessive weather helm compared to other classes. I used to see many sailors break rudder blades at Panama City FL from sailing in heavy air, off the wind, with straight down blades. Sweeping the blade back will move the pressure from the tip, and move it up towards the middle of the blade spreading the force over a greater surface area. Another advantage of having some sweep on the flat rudder blade means moving the rudder less - reducing the braking effect of the straight-down blade. Good Sailing.
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Comments

Thank you Hank for getting the forums back on-line! Weather H

Submitted by Scott Mauney on Thu, 12/09/2010 - 20:44.
Thank you Hank for getting the forums back on-line! Weather Helm #2 How did this come to my attention? At the 2005 FS NAC I put the strap on the rear bolt by accident. When we went out before the first qualifier, Bill Draheim, the skipper told me he had severe lee helm. Finally I realized what I had done. We had no time to change it so we kicked the rudder blade back to where the aft tip was almost out of the water - to balance the excessive lee helm. We sailed the remainder of regatta with strap in the normal forward bolt location. When I got my new boat I decided to experiment using the 3 new holes. Final analysis: I use the forward hole up to 8 knots of breeze and the next hole back at 1&1/4" for anything over 8 knots. Here is a link showing the second hole. I just add another stainless bolt and nut and move the strap back. Draheim told me the helm feels like a Melges 24 with the strap in this position. [ed. Here's a Picture:] photo of rudder head attachment

Perhaps some clarification is in order here.

Submitted by karafiath on Fri, 12/10/2010 - 13:42.
Perhaps some clarification is in order here.The sheet attachment point on the rudderhead tends to be behind the extension of the rudder axis of rotation defined by the rudder pin. This is true for the factory position and more so for the further aft positions that scott Mauney used. Thus the main sheet forces tend to relieve the force that you perceive at the tiller end. The moment that the mainsheet induces on the rudder is in the same direction that the skipper induces to keep the boat from rounding up into the wind.The rudder angle needed to maintain course remains the same. So the question is really a matter of skipper preferance. Does the skipper want to instantly feel the effect of for example a puff instantaneously via feedback through the tiller force or does he want to relieve the tiller force by moving the sheet attachment point further back on the tiller head? In handling too much weather helm in high winds I pull up the centerboard a bit at a time until the helm becomes balanced, and when a puff hits I feel it on the tller and round up a tad, hike harder and ease the sheet a tad. The centerboard has a better hydrodynamic shape than the rudder and is a more efficient surface than the rudder for creating the sideforce needed to minimize leeway, therefore a neutral rudder angle or (nearly neutral) is best. Gabor FS3512

[?]yes I agree, The adjustment indicated to the mainsheet attach

Submitted by matruax on Fri, 12/10/2010 - 14:42.
[?]yes I agree, The adjustment indicated to the mainsheet attachment point on the rudder will change perceived forces on the tiller but doesn't change the weather helm. Weather helm is a result of the relationship between center of pressure(sails) and center of balance (hull and centerboard). moving the attachment point for the mainsail does not move the center of pressure. Raising the centerboard does move the center of balance aft and should reduce weather helm. Correct my physics if I'm wrong Mark