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Old 09-05-2011
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Keel Bolt Torque

I have a question for the members - does anyone know any engineering rules that would allow calculating the torque required on a given keel bolt or bolts?

The reason I ask is that the general attitude seems to be "more is better", "crank on them until they squeal", or "put a pipe on a breaker bar and pull until the suckers scream for mercy". I've never seen anything much more technical or sophisticated than that.

I've always understood that a specific torque is required in order to stretch the bolts properly to achieve proper clamping force - this varies with the size of bolt, material it's made of etc.

Also, high torque is required to compensate for powerful, high frequency repetitive or rotational forces - engine cylinder heads, road wheels etc. not static loads where the bolts are only "locating" the parts in question.

To my eye, a keel falls somewhere in between these extremes - repetitive flexing forces from the boats motion but not really high frequency. Considering that such highly loaded fasteners like cylinder head bolts, connecting rod bolts, main bearing caps etc. are only torqued to values like 80 Ft/Lbs, I don't understand the need for keel bolts to be run up to 150 - 300 Ft/Lbs, especially considering they are generally stainless steel which I understand compares to, at best, a grade 3 fastener. It seems to me that these extreme torques are only going to crush the hull material, overstretch the bolt and/or risk galling the fasteners.

Anybody??
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Last edited by SloopJonB; 05-04-2014 at 07:39 PM.
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