Submitted on May 15, 2006 by Tim Hooper

Question: Hello there,

I am wondering if you can help me with a problem in balancing my boat better.

The boat is an Australian designed Northshore 27, designed by Hank Kaufmann in the early 80's. It is fractionally rigged, with a main of about 195 sq. ft. and a number 1 of about 190.

My problem is excessive weather helm.

On the breeze, even in winds of 10 to 15 knots apparent, I find that to balance the boat for even a relatively balanced helm, I am luffing the main excessively. I have tried everything I can think of from flattening the main and dropping the traveller to changing the draft position of the heads'l.

The only vaguely succesful adjustment I have made is to reduce the tension in the lower shrouds to allow the backstay to work more effectively. My aim was to allow the mast to bend below the capstays to help flatten the main, but I wonder whether this is also moving the centre of effort forward. Either way, it immediately eases the helm!

Again, this made me wonder about the rake on the mast, however on measuring things, I have found that the mast is raked by no more than about an inch to the spreaders and is pretty plumb at that point...from there there is about 10 inches of pre-bend above. It doesn't sound like a lot of rake to me and given that I do not have an adjustable forestay, there is no simple way of testing this.

The only other thing I can think of before I start taking drastic measures is to look to see whether I can change the position of the centre of effort on the main by reducing the foot and thereby moving things forward. The boat has been completely re-rigged inc spars and I have no datum as to the manufacturers original intentions. (I have spoken to them and because of the age of the boat they are unable to help me).

By all intents and purposes, I believe the boat should go better up-wind in the 10-15knot range both in terms of pointing and speed but I am struggling as to know what is the next logical step...

One final thing is that if I carry my heavy no1 into the range described, I tend to get a better result than running the number two - obviously this is to do with the sail area forward and c of e...

One final question is that as you can see by the drawing, I can happily work out the CofE for the individual sails, but how do you bring that together for the overall?

I tend to think these questions might require responses from riggers, sailmakers under-body specialists and of course better sailors than me!
However you thoughts would be appreciated!

Kind Regards,
Tim Hooper

Answer: Hi Tim,

Based on a glance at the sail plan you sent, the rudder area represents a large part of the underwater lateral surface. Also the rudder is hung on pintels so, compared to a boat with the rudder blade balanced on a rudder post, you will feel every bit of helm that the sail plan is producing.

Weather helm is the result of the balance of the sails over the keel and rudder, and the amount of heel. More heel makes more weather helm because when you heel the boat trys to turn the boat into the wind, so you need to use the rudder to turn it back away from the wind. You can reduce heel by flattening the sails. When you flatten the sails the center of effort automatically moves forward which should also help to reduce the weather helm.

You did not say if your mast is deck stepped or keel stepped. However, if the problem is better with the lower shrouds eased, and you are really sailing with 10" of prebend, then it is safe to say that your mainsail is too deep and your headstay is too long. You are probably losing rig tension when you tighten your backstay because the mast is so far out of column that the headstay and shroud intersection on the mast is getting closer to the deck the more you pull on the backstay. In other words, your mast tube is allowed to compress and the headstay is allowed to sag to leeward. Another negative consequence is that the mast can pump in waves, which causes the mainsail shape to continually change, which in turn requires more leech tension to keep the sail from flogging. A stiffer rig with less movement will allow you to trim the mainsail leech with less pressure on the mainsheet. Less mainsheet tension means less weather helm.

A 27' fractional rig would normally be set up with about 2-3" of prebend. In 13-16 knots of wind you would want the lower shrouds to be nearly as tight as the upper shrouds. With tighter lowers you essentially have a stiffer mast. When the mast is stiffer, you can put more pressure on the backstay to get the headstay tight, because the mast section will not compress as much.

You said that you have a small amount of aft rake at the spreaders, and 10" of prebend. Rake is typically measured at the masthead or hounds. You probably have 4-5" of rake at the top of the mast. By shortening your headstay you will make the mast straighter and stiffer and move the center of effort forward.

Best Regards,
Dan Neri

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