Re: [Cal_Boats] hull speed, 4-107's, and maybe more! (Chris)

My "theoretical" hull speed is 7.65 knots and I have never exceeded it, but have sailed right at it. The only measurement that "matters" is the speed through the water. A GPS speed cannot compensate for any current and a body of water that you believe has no current could still be "moving" based on tidal and/or wind flow that you cannot directly see and/or the periodic acceleration of the water at the top of waves. My hull speed run was on a beam reach with both main and 135% genoa fully deployed and a steady tropical depression generated wind speed of 35 knots across Galveston Bay in Texas. I had no GPS but my knotmeter measured steady 7.55 - 7.65 knots through the water for over an hour and a half. The standing wave theory was quite apparent and pronounced as you could stand on the high side of the boat and watch the water smoothly leave the bow, dip way down the hull and exit the hull right at the aft meeting of the hull and the water! On higher gusts the boat speed would not go above 7.65, but the bow would sink deeper into the water and I would turn up a few degrees to decrease the pressure on the sails and luff the main right at the mast. It was one of the most exciting sails that I have ever had on my boat and was soon followed by the docking and stripping of all canvas as the tropical depression approached Seabrook, TX that was supposed to go into New Orleans according to all of the forecasts. I have been a firm believer in the 1.34 X the square root of the waterline length ever since. Smaller, lighter keelboats that exceed this limit are probably planing and lifting out of the water momentarily, especially if you are watching your speed on GPS rather than knotmeter in the water and also if you are riding the crest of a wave. I certainly might be wrong, but the rule has held firm for my boat and my experience! Don Dutton, 1986 Cal 33-2, "Quantum Evolution" From: Chris Campbell <cl… [at] charterinternet.com> To: Ca… [at] yahoogroups.com Sent: Monday, October 13, 2008 10:49:09 AM Subject: Re: [Cal_Boats] hull speed, 4-107's, and maybe more! Tom Vandiver wrote: Hi Reg and Barb, 1.34 X square root of the water line length is theoretical max. I've been reading this rule for years. If my Cal 20 has a waterline length of 18 feet, the theoretical top speed is 4.24 (statute or nautical???) miles per hour. She'll exceed that if the crew breathes heavily, as measured by GPS in current-free waters. This is not one of the CCA rule boats with long overhangs that supposedly immerse the ends when they heel and gain LWL (I've become suspicious of that theory too). What do others know about this theory? Is it akin to the obvious truth that the sun orbits the earth? Chris Campbell