Thanks for the informative reply. I don't actually have a problem with alignment, however as I currently have the
gearbox out of the boat to replace the engine rear
oil seal and vibration damper between engine and gearbox, (the original has failed)I thought that adding a flexible coupling would be an improvement to the boat- In the med, we have to do a lot of motorsailing, which can result in temporary engine/prop misalignment due to
hull flex caused by the stresses from sailing whilst the engine is running. The flexible coupling should overcome this. (I've bought the R&D vibration damper, and saw their flexy coupling while researching the vibration damperon the 'net). I will set up the engine/propshaft alignment when i
rebuild it, the cutlass bearing is OK and the engine mounts and
cradle are good.
I note the points you have raised from Dave Gerr's book, I reckon my engine mounts are pretty stiff as they currently have to reduce engine movement as much as possible and absorb 100% of prop thrust. Your point has made me think about the possibility of setting up some harmonic vibration within the propshaft assembly, which clearly wouldn't be good, so i think i may not use the flexy coupling until I've seen how it performs with the new vibration damper