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  #1  
Old 07-20-2008
DrB DrB is offline
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Weather/Lee Helm

I own a Pearson 10M. The 10M is a Bill Shaw design.

Was out in it today and want to understand if what I think I have, lee helm, is real or imaginary.

First of all, I don't think a Bill Shaw designed boat has lee helm, but maybe with my boat, for some reason, I have it.


Particulars:

Today's conditions: 5 to 8 knots of wind.
Boat speeds from 2 to 5.5 knots (GPS)
Waves: Minimal 1 to 2 feet
Sails: 135% Genoa, Main - Both pretty blown.
Maximum heel angle: 8 deg , 0 to 5 deg most of the time
Backstay Tension: 1000 psi.

Unfortunately, I didn't have more wind to get the boat to heel more to really see if I had weather/lee helm.

In these light air conditions, I would set the wheel to a neutral rudder, take my hands off, and the boat would sail a straight course for almost 15 seconds without deviation and then start to head down wind. If I turned the wheel so that the rudder had 1 or 2 degrees angle to the weather, i.e. turning a little upwind, the boat would hold the same heading for 25 seconds then start to head downwind.

A few questions:
  1. Is this true lee helm or nothing really since I didn't really have the boat heeled over?
  2. If it is lee helm, can inefficient or blown sails be the cause of the unbalance?
  3. If the one sail is more efficient that the other can that significantly affect the balance.
  4. Since I can't believe a Bill Shaw designed boat would have lee helm and if I do have it, what can I do to correct it? Would adjustments to the rigging help?

Thanks.

DrB
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Old 07-20-2008
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DrB, I think you are correct in that your P10M was not designed with lee helm. IIRC, designers strive for around 3 but no more than 5 degrees of weather helm. This gives the boat better performance with reguard to the sail to underbody efficiency without creating excessive drag from either.

I am certainly not a designer by any stretch, but have read that if your sails are in fact too full (blown), that in particularly the main is your prime source of up wind power. And if the shape is too full, therefore creating drag and the main is less efficient. This would allow your 135 to push the bow to leeward causing lee helm.

When sailing on others boats, especially ones with larger genoas, on up wind angles (as in close hauled) I found that I was closing the slot between the genoa and the main by flattening the genoa too much. This of course decreased the mains efficiency and caused slight lee helm.

I'm sure someone will be able to explain this far better than I, but this could be a factor in the cause of your lee helm, IMHO.

Bob

Last edited by fullkeel7; 07-20-2008 at 11:56 PM. Reason: sp
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Old 07-21-2008
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Most any boat can be tuned either lee or weather helm. I wouldn't judge much but the light winds you had. Wait until you get at least 10-15 and see how you can trim things. If you still have lee helm and can't balance things using the sheets, traveler, etc. then it's time to start adjusting the mast position.
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Old 07-21-2008
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And I think 1000 pounds was a bit much for backstay tension in 5 knots. That's a lot of pull on a boat that size.
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