Regarding bolt torque and corresponding bolt pretension: there seems to be some misunderstanding about bolt torque. Worries about stripping threads when boat is in the water, thinking about lifting the keel up, must do it on the hard, etc.
Just as an example for the sake of discussion, let's consider a 1" diameter, 316 bolt * Fy = 30 ksi = 30,000 psi (yield strength) * Fu = 75 ksi = 75,000 psi (fracture strength) * Area = 0.79 in2 * Area through threads approx 0.60 in2 The correlation between torque and bolt pretension is not high due to the many factors involved, but generally, a commonly used approximate relationship is as follows: T = (K x D x P)/12 K is a torque or friction coefficient, D is diameter, P is pretension force. K = 0.20 would be common. Rearranging the above to solve for pretension: P = 12T/(KD) Lets also presume, again for discussion, that the 1" dia 316 bolt is pretensioned to 60% of yield. That means the pretension force: P = (0.60) x 30,000 psi x 0.60 in2 = 10,800 lbs T = (0.2 x 1" x 10,800)/12 = 180 ft-lbs Which is certainly in the torque range suggested in recent posts. Let's take these numbers, again for discussion and consider a boat with (8) 1" diameter keel bolts. The pretension total would be: 8 bolts x 10,800 lbs/bolt = 86,400 lbs. The weight of the keel (4000 lbs? 6000 lbs?) is not particularly significant -- it's within the margin of error of this entire calculation and then some. Observations: * Concerns about lifting the keel and causing damage are unwarranted * Doesn't matter much at all whether the boat is in the water or in the cradle * Bolt torque is the torque is the torque -- it doesn't matter if the boat is in the water or not relative to stripping the threads. Sorry for the very long post, but wanted to help out with some of the discussion. I intend to torque my keep bolts this spring and have read the posts on this subject with interest. Best, Jeff Laman 1981 C&C34 "Harmony" Ludington, MI
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