Robert Biegler: Finding the Centre of Effort

Empirical method for finding the centre of effort of sail, boat and crew for a sailing kayak with a small sail, where wind pressure on the crew is likely to be a significant factor. Find shallow water, ideally up to the shoulder of someone sitting on the bottom. Tie a bridle to bow and stern, have the person who sits in the water hold the line that is attached to the bridle. Adjust forward and aft legs of bridle so that the boat's angle to the apparent wind is the same as expected when sailing upwind, sheet the sail accordingly. Your helper sights along the line that is attached to the bridle and tells you where a continuation of that line (shown here as a stippled arrow) intersects with the midline of the boat. Marks that spot. Repeat with the bridle adjusted so that the apparent wind angle is a reach, sheeting the sail accordingly. Again, mark the spot where a continuation of the third line intersects with the midline of the boat. That gives you a range for the centre of effort for courses from on the wind to a reach. Mount leeboards so that a point one quarter from the leading edge of the leeboards when they are vertical is in the middle of the marked range. Make sure you can adjust the rake of the leeboards.