Sail Trim Finesse
Back Winded Mainsail
We are on a close haul at 30 degrees to the wind. I want you to check out this photo and have a good look at the shape of the mainsail. The photo is taken on the windward side of the boat.
Look at the black seam line. Good or Bad?
Well it is doing exactly what I wanted it to do. The front of the sail is curved in on itself – but why?
On this day we had about 15 knots of wind and I had not yet reefed the mainsail BUT we were over powered. So I eased the mainsail traveller out a little but keeping the head sail in tight. This back pressured the leading leeward edge of the mainsail causing it to create an “S” shape. This pressure comes from back eddies at the forward leeward side of the mainsail and from pressure gathering between the main and the headsail pushing the leading edge to windward. I do this often prior to reefing. Effectively it reefs the sail. If you look, only the trailing last half of the main is powered up making the sail act almost exactly like it is reefed. BIG NOTE: the sail is not luffing. It is constantly in this shape if you’ve got it adjusted just right.
Back Winded Mainsail diagram
This effect can be seen in the image below. While I am the first one to recommend reefing the sails, this little trick can help you out when riding just on the edge. Try it next time you’re out.
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