I believe it is boat length at waterline. (15F 10in for 17 as I recall) cheers, Shawn Boles Grey Mist (M17 #276 1978) -----Original Message----- From: montgomery_boats-bounces+shawn=ori.org@mailman.xmission.com [mailto:montgomery_boats-bounces+shawn=ori.org@mailman.xmission.com] On Behalf Of David C. Patterson Sent: Wednesday, August 19, 2009 11:45 AM To: montgomery_boats@mailman.xmission.com Subject: M_Boats: Chip log formula for M17 is really simple This may be of interest among list members. Since I am sailing without a knotmeter, I learned from my ASA Coastal Navigation class last winter how to estimate speed handily. The Chip Log Formula goes: .6 (a constant) X boat length divided by seconds = boat speed in knots. A knot is about 1.1 mph. What is handy is that for an M17 .6 x 17 = 10.2. Rounding that to 10 makes the division simple. I get curious about boat speed especially on a run, when is so deceptively even (usually). Spotting a leaf, bit of debris, or even some foam ahead, I watch for it to reach the bow of the boat. Then counting "one one thousand, two one thousand.etc." I get my seconds, divide into ten, and I have a speed estimate. Any three or four syllable word works easily, as in "one rutabaga" (my youngest daughter's old favorite), or "two Montgomery", etc. So, three seconds means a little over three knots, two seconds means five knots of speed. (What is theoretical hull speed on an M17 anyway?) The same formula for an M15 ends up with exactly 9 divided by the seconds. Perhaps even handier. Enjoy the too brief sailing season, David M17 #393 _______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats Remember, there is no privacy on the Internet!