Hi Stewart, gosh, my mistake, about calling my flexable coupling, a “National” coupling.
I checked the internet and found my coupling to be a “Federal” flexable coupling, check this address for photo and more info :
I will take a photo of the installed Federal Coupling, next weekend, and will forward that .
I had to use the standard bolt together flanged couplings to get the shaft alignment as close as I could, then removed it and installed the “Federal” flexable coupling.
There is a very interesting problem that cropped up on my boat, due to the Volvo 2002 and the standard flanged coupling.
For some unknown reason, the f/g shaft log, that holds the cutless bearing, broke it’s resin seal/mounting to the hole through the deadwood, and this allowed saltwater to go up the outter sides of the shaft log, then down into the deadwood below the shaft.
This always caused high moisture readings in the deadwood area.
It seems that during hull construction, the internal deadwood area was filled with glass fiber, (guessing that it was floor sweepings), then polyester resin was poured in to fill the voids.
Well, all the voids were not filled, and that is where the incoming saltwater collected, which intern, created the high moisture readings.
I think that a previous owner got something tangled in the prop, and instead of stopping and clearing it, drove on, and the shaft may have gotten bent, driving on with a bent shaft could have jarred the shaft log loose from it’s resin bond, while it was destroying the cutless bearing.
It was a long tedious proceedure to back pressure-remove the water from the dead wood area, and re-seal the shaft log, all of this could have been prevented in the first place, had a flexable coupling been installed, first, as it would have been able to absorb the bent shaft vibration loading on the cutless bearing and the shaft log.