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Old 02-13-2009
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Quote:
Originally Posted by frogman27 View Post
Just a couple thoughts, based on the standard calculation used, in order to get 6 knots you need at least 25 feet of waterline. Since length overall is usually longer than waterline you're probably looking at 27+/- feet to get that. There's only one trailerable I know of that's that long (the seaward 32rk), and it's way out of budget consideration. In the sizes you're talking about you get a boat with 4.5-5 knot abilities and you'll average 3.5 or so if you keep it lightly loaded.
Short threadjack: the theoretical hull speed calculations are pretty good yardsticks for large, pure displacement vessels. But smaller, lighter boats can and frequently do exceed hull speeds; think of them as semi-displacement hulls, or semi-planing hulls if you prefer. Here's an example: our SJ21 has a waterline length of only 17.5ft, yet it regularly pushes 7 kts on the GPS without surfing and on most points of sail. From a GPS log (and Garmin rounds down):

277 6/15/2008 11:27:06 AM 4703 ft 176 ft 0:00:19 5 kt 240° true N42 31.635 W105 00.272
278 6/15/2008 11:27:25 AM 4711 ft 144 ft 0:00:15 6 kt 241° true N42 31.620 W105 00.306
279 6/15/2008 11:27:40 AM 4720 ft 210 ft 0:00:22 6 kt 240° true N42 31.609 W105 00.334
280 6/15/2008 11:28:02 AM 4727 ft 200 ft 0:00:21 6 kt 236° true N42 31.592 W105 00.375
281 6/15/2008 11:28:23 AM 4735 ft 191 ft 0:00:19 6 kt 239° true N42 31.573 W105 00.412
282 6/15/2008 11:28:42 AM 4744 ft 50 ft 0:00:05 6 kt 235° true N42 31.557 W105 00.448
283 6/15/2008 11:28:47 AM 4747 ft 234 ft 0:00:24 6 kt 235° true N42 31.552 W105 00.457
284 6/15/2008 11:29:11 AM 4755 ft 194 ft 0:00:20 6 kt 239° true N42 31.530 W105 00.500
285 6/15/2008 11:29:31 AM 4761 ft 197 ft 0:00:21 6 kt 231° true N42 31.514 W105 00.537
286 6/15/2008 11:29:52 AM 4764 ft 183 ft 0:00:20 5 kt 224° true N42 31.493 W105 00.571
287 6/15/2008 11:30:12 AM 4764 ft 96 ft 0:00:16 4 kt 203° true N42 31.472 W105 00.599
288 6/15/2008 11:30:28 AM 4764 ft 128 ft 0:00:17 4 kt 74° true N42 31.457 W105 00.607
289 6/15/2008 11:30:45 AM 4768 ft 139 ft 0:00:16 5 kt 80° true N42 31.463 W105 00.580
290 6/15/2008 11:31:01 AM 4766 ft 204 ft 0:00:20 6 kt 63° true N42 31.467 W105 00.549
291 6/15/2008 11:31:21 AM 4766 ft 178 ft 0:00:18 6 kt 35° true N42 31.482 W105 00.509


We fell below theoretical hull speed once, but that was a tack. That's why I endorse smaller, lighter boats on little inland lakes; they sail like dinghies, keeping the fun factor high while ownership costs stay low, and they are dead simple to plop in the next lake over when you get sick of this one. /threadjack
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