Israeli Corvette propeller blade bolt failure

Right. If you're diving, it'd be a lot easier to use an ultrasonic tool than to get in there with a little micrometer trying to measure something in ten-thousandths. When you've got your gloves on and stuff, ten thousandths is sort of a joke. This bolt, as I remember, came off an Israeli Corvette propeller. They were cracking — there are cracks right under the head. When we were cleaning up the lab a couple of weeks ago I retrieved one.

Physical-object teaching unit. Tom passes around a tapered-shank Monel bolt designed for stretch-measurement preload, used to hold variable-pitch propellers. Bolt has a fatigue crack under the head; Tom does not remember why they were loosening. Used to introduce sophisticated bolt design as a class of engineering practice.

This one came off an Israeli Corvette. A Corvette is like a small frigate, which is like a small destroyer — like a big PT boat. This was holding the variable-pitch propellers on. Nowadays they have a shaft coming down through the propeller shaft that allows you to change the pitch of the propellers depending on the speed you want to go, because there's no one pitch that's perfect for all velocities.