Originally Posted by perchance
Generic torque charts
for fasteners should be available online. Although they won't be specific to your application and are based on bolt size but should do.
This was my first inclination too. We buiild machines and we know to torque bolts to chart values or at least to some tensions in excess of the expected maximum cyclic loads to avoid parting of the joints or fatigue. The problem in boat systems is that you are squeezing a composite structure instead of metal. I think that the charted tensions assume metal joints and may be too high. I suggest the best source is the builder
if the data can be retrieved. Make sure the chart values you use are for the bolt material at hand. This can easily vary 2:1.
There are on-line sources to estimate tension from bolt torque and thread pitch
. If you can't find any difinitive source for your boat, calculate the torque needed to equal the tension due to the keel weight. Add to this the additional tension applied to the bolts as the boat heels. You will need to estimate the center of mass of the keel and the heel angle and apply this force to calculate an bending moment. This moment must be resisted by the keel bolt spacing across the width of the keel. In short, calcuate the foot-# of overhung torque and divice by the spacing (ft) of the bolts. This is the bolt tension needed to keep the keel base in contact withthe hull
. Add this to the above tension only number. Add a safety
factor. I suggest about 150%. If it is a race
boat or otherwise is subjected to a lot of impact you may want a greater factor. Compare this number to the charted maximums you might look up just for a sanity check. Don't exceed the chart numbers. Remember that the keel 'weighs less' in the water
by the volume of water displaced by the keel.