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November 2008

Below is a reprint of an article I wrote for the Open Canoe Sailing Group's in-house publication "The Gossip", which was published in the November 2008 edition.

 

One disadvantage with having a bigger sail than most other OCSG members (mine is 5.8m2/62 sq ft) is that you can sail inefficiently and still arrive at the destination before others, masking the problem. It was obvious to me that I was not pointing into the wind on my Raptor as much as other craft but I felt no real pressure to do anything about it, as I felt I could keep up with the majority, even if this entailed me making many more tacks than them. Eventually, however, I decided to look at why it seemed that I couldn't match the windward performance of others. I discussed the matter with DaveS and he felt the main problem was with the Raptor's rigging. The standard rigging uses an outhaul line from the sail clew to a block on the end of the boom to control the shape of the sail and the only way of tensioning the sail leech (to reduce "spillage" of air from the top of the sail) was to tension this outhaul line. The problem with this is that it also resulted in the foot of the sail being pulled flat, which resulted in a poor aerofoil profile and loss of drive in the main part of the sail. Only the upper part of the sail retained its shape and drive, but this part of the sail also gives the most tipping effect, increasing the tendency to capsize. Of course, I could simply trim my sail with a good shape in the foot and not tension the leech at all, but then I would lose some of the available sail performance. So I needed to find a way of achieving a good shape in the entire sail area.

Dave did not think there was any intrinsic reason why the Raptor couldn't point into the wind as well as any other boat. He believed it was simply that the performance dropped off so markedly when sailing close-hauled that I felt I was pinching too much and would bear away. His approach was to improve the overall sail performance so that I could maintain a reasonable speed when sailing upwind and would not be tempted to bear away, resulting in overall improvement in my Velocity Made Good (VMG) i.e. speed of reaching a set destination.

We had a brainstorming session while at this year's Loch Tummel meet and decided that the best approach was to have a separate leech tensioning line. Dave also thought a stiffer boom would help the Raptor's performance. The standard carbon fiber boom is tapered and surprisingly small. By using larger diameter tubing, the boom would flex less in gusts, reducing the loss of leech tension and spillage of air from the sail. The solution that we decided on after a certain amount of trial and error, was to install a 2" aluminium boom with a leech tensioning line block attached to the boom with a prussic loop, which allows me to slide it along the boom so that it is at the optimal position (directly under the sail clew). I can now set the desired draft in my sail and then tighten up the leech. Solway Dory made my new boom and installed an additional cleat for the new leech line.

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