Hi GArdner, Which design is this? I can tell you how I sailed the last time I was sailing Sidecar - which seems an average cruising Harry. It was not an issue of cspsize, but the feel of the force on sheets and speed in the waves. I wanted to slow her down once the speed was enough for the state of the seas. Thestress of tillering along with big gusts of wind gets too much yuo want to take down some sail. Well, from Albany, it was a typical summer's day, with actually light calm at dawn, then a useable 5-10knots up untilabout 10 O'clock after which the sea breeze started to build up. I had breeze rising up to about 15knots at 11 Or 12 O'clock and put in the first reef. Then at about 2 O'clock it was up to 20 knots and I went down to no sail (second reef Point). The speed was still a constant 8-9knots average ever since about 11 o'clockam. Doug --- On Thu, 14/4/11, Gardner Pomper <gardner@networknow.org> wrote: From: Gardner Pomper <gardner@networknow.org> Subject: [harryproa] How to calculate force on the sail? To: harryproa@yahoogroups.com.au Date: Thursday, 14 April, 2011, 0:26   I have been playing with stats for my designs, trying to get the SA/D and Bruce number up, but it doesn't help me in real life if I have to reef when the wind hits 4 knots <grin>. How do I calculate the location and magnitude of the force on the sail, so that I can determine what wind speeds I need to reef at, or take the sails down altogether? I am willing to ignore the effect of the mast bending and use that as a safety factor.   - Gardner Pasadena, MD