Shaft Nut Configuration
Want to start an argument in most any boatyard?
Find a boat where the shaft nuts are in this configuration (thick nut first, thin nut last) and tell the owner or yard manager who installed it that they're backward. It seems like a no-brainer that the larger nut against the prop would do most of the work and that the smaller nut should go on second, to kind of hold it in place.
In truth, however, it's the smaller nut that should always go against the load because it is the "jammed" nut, not the "jam" nut. When the second, outer nut is tightened down, it compresses and deforms the inner nut a tiny bit, rotating it a fraction of a turn. This effectively unloads the threads of the first nut and engages the threads of the second nut. Thus, the top or outer nut actually takes all the load. As the larger nut has more thread area (and more holding power), that's the one you want as the outer nut. I see prop nuts installed backward all the time while surveying. Will the prop fall off because of it? Not likely. But who wants to find out?