Wednesday, August 23, 2006

Rooting out Boatspeed Issues

In an effort to achieve maximum boatspeed and figure out our pointing issue I came across this explaination from Ullman Skelly Sails regarding Tuning and the" J dimension". I took the opportunity to measure as much of the bottom of the boat as possible when it was out of the water for Kingston. The one thing I have not measured yet (or paid enough attention to) is the mast height and forestay length. This article seems to get at the root of our problem, and gives solutions that are worth investigating. The following is an excerpt from the Ullman Skelly Sails site.

The J-24 has an inherent problem of leeward helm. Leeward helm is evident when the center of effort above the waterline is too far forward in the boat, meaning the boat is not well balanced. The problem of leeward helm can be detrimental to boat speed and pointing ability, especially in light air. Leeward helm will make it difficult to steer the boat to windward where a balanced helm or a slight amount of weather helm will help the helmsman keep the boat in the grove while sailing very flat. “The flatter you can sail a J-24 to windward while staying in the groove, the faster the boat will go!”

By shortening the mast to minimum and lengthening the headstay and J measurement to maximum, you move the sail plan as far back as the class rules allow. Raking the mast aft will move the center of effort aft in the boat, which will induce more weather helm in the boat.

Note: If possible, we recommend having a certified J-24 class measurer mark your minimum mast length, maximum headstay length and maximum J. To cut your spar as close to class minimum as possible, you will need a class jig. There seems to be some discrepancy from one boat to another to exactly where the stem/sheer line point is at the bow. This point can make a big difference in your headstay length and J dimension. It is crucial to your upwind light air performance to have the mast length as close to minimum and the "J" measurement and headstay length as close to maximum as possible.

4 Comments:

Blogger Pat said...

I guess there's also an issue with refairing keels of older J-24s and with having enough crew eight to balance the boat when a genoa is up.

5:10 PM  
Blogger Pat said...

whoops crew weight, not eight ... unless it's an extraordinarily windy day?

5:10 PM  
Blogger the skip said...

I will be looking into fairing the keel for the next season or season after that. We are currently looking at dry sailing the boat soon. i do not want to do any serious keel and hull work till we are ready to dry sail.

Thanks a million for your excellent comments Pat! Much appreciated.

9:02 AM  
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11:17 PM  

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