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-   -   Can a couple of inches make a big differnce? (http://www.sailnet.com/forums/sailboat-design-construction/40508-can-couple-inches-make-big-differnce.html)

belanich 02-11-2008 10:02 AM

Can a couple of inches make a big differnce?
 
Two years ago I bought a Pearson 30. I was new to sailing and learned a great deal the first year. During that first year the boat had a significant amount of weather helm. Most of the time it was not much of a problem, but when the breeze kicked up or during a gust the boat was hard to control. I first thought it was my inexperience - I read about different ways to fix weather helm but nothing worked. Since I had no experience on other boats I figured it was the normal feel of a sailboat that size and I would have to live with it.

Between seasons I removed the mast step to fix a leak that was running down the compression post. The compression post had been replaced by a previous owner because of this very reason. I noticed that only the last 2 inches (aft) of the mast step were over the compression post and that the forward part of the mast step was crushing the cabin top.

I measured the distance from the stem fitting to the mast step and it was 4 inches off. I glassed over the hole in the cabin top for the wiring and rerouted the wires outside of the mast and installed the mast step directly over the compression post.

Last season the excessive weather helm was gone! I notice this immediately the first day I sailed. Now I have a slight weather helm, she accelerates faster and I have a greater top speed in less wind. During a gust I have control.

Is it possible the moving the mast step 4 inches can have this great effect on sail balance?

MB
Leapfrog

blt2ski 02-11-2008 10:11 AM

very possible. I had some issue with an 8' pram I had as a teen. used a sail from another dinghy, a bit bigger, but the center of the sail was too far back in this case by about 9", got the designed for sail, and it sailed beautifully!

So yes, that 4" could make a difference!

marty

max-on 02-11-2008 10:14 AM

Did you reposition the mast 4 inches forward or aft from its previous location?

belanich 02-11-2008 10:20 AM

Quote:

Originally Posted by max-on (Post 263739)
Did you reposition the mast 4 inches forward or aft from its previous location?

The mast step was too far forward so I moved it aft.
MB
Leapfrog

Maine Sail 02-11-2008 10:28 AM

Yes and mast rake can also play a big role in weather helm as well as sail trim.

Having sailed and raced on quite a few P-30's I can honestly say they are well balanced boats and generally do not have lots of weather helm when trimmed and dialed in properly.

chucklesR 02-11-2008 10:53 AM

Shifting the base of the mast aft changed the balance by moving the center of effort aft. It also changed the relationship between your jib and main - and the slot between the sails by opening the slot up.
All other things being equal - the rest of your rig etc.. - did the move increase or decrease the rake of your mast? IMHO it may have tightened your backstay and pulled excess fullness from your main (especially if its a older main with the baggies).

Any number of factors may have changed your boats balance, certainly shifting the mast base aft would make a significant change. Designers agonize for days over calculations to get it 'right' then hope it all works once the boat is in the water.

Generally weather helm (and heeling) is corrected/reduced by

1. 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 (s/b flatter).
2. 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.
3. 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 with windex, twist at the top will allow wind to spill.
4. Move the Genoa lead aft to flatten the the lower section and twist off the leech.The luff of the main bottom batten should line up with boom, top with windex, twist at the top will allow wind to spill
5. Dropping the boom to leeward (via traveller) after shaping will reduce weather helm.

Aasem 02-11-2008 11:12 AM

If the base of the mast had slipped forward by four inches, that's likely to have induced a shitload of unwanted rake. That can induce excessive weather helm. By restepping it properly, it sounds like you solved the problem. Congrats!

sanctuarysam 02-11-2008 03:55 PM

i'm so gonna get in trouble for this post
 
:D

uhm..ask any woman if a couple of inches matter.
chances are they will give you that special look as to say.."uhm yeah..a couple of inches matters a lot"
oh..are we talking boats....?

belanich 02-11-2008 04:15 PM

ChucklesR,

Before the mast step was moved aft I tried all the suggestions you just outlined but could never completely correct the problem. I now see that this made learning to sail the first year more difficult. Not only was it difficult to properly trim the sails, with too much weather helm you can't feel the rudder though the tiller which makes steering diffecult.

With the mast step in the current location the mast is raked more forward - I know this only because when the mast was stepped last spring the backstay had to be let out significantly for the clevis pin to fit. Now I can feel small changes in water pressure against both sides of the rudder when I move the tiller. Now I can steer a straighter course and adjust with changing wind pressure - this is a huge advantage when learning to sail.

MB
Leapfrog

belanich 02-11-2008 04:19 PM

Quote:

Originally Posted by sanctuarysam (Post 263902)
:D

uhm..ask any woman if a couple of inches matter.
chances are they will give you that special look as to say.."uhm yeah..a couple of inches matters a lot"
oh..are we talking boats....?

Well I have noticed that with less weather helm my wife is now more willing to grab my tiller... I mean THE tiller more often. :D
MB


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