J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Flexible shaft couplings

How many have installed a flexible shaft coupling? And did it make any difference.?
We are replacing our prop shaft and considering a shorter shaft by 1.25in to accommodate a flex coupling..(R&D Marine 910-002)..hoping to reduce vibration from the old Yanmar. Will also be replacing the cutlass bearing.

I installed one on Rhapsody (picture at this post). Proper shaft alignment is still needed. check this post. Make sure you bypass the coupling with an electrical ground jumper wire to prevent prop electrolysis.

Good info. - thanks! Do you think the flex coupling helped reduce vibration - and noise transmission? That would be my only reason for installing one. The alignment has always been good, but the old shaft - 40 plus years old - was worn down at the cutlass bearing as well as the key sheared off at the transmission end last year damaging the shaft and coupling so we are replacing it all. The original 2QM15 is a noisy and unbalanced beast anyway so a flex coupling may just be a waste of money in my case. There was a note in the Yanmar service manual that claims a flex coupling must be installed if the engine is mounted with flexible mounts - which started me thinking that our installation should have had one. It has a steady throb at cruising speed (2200 rpm) that rattles the whole boat. Prop was serviced and balanced by Martek recently.

It helped a little, but not much. A straight shaft, good engine mounts (one where the rubber isolators haven't degraded over the life of the boat) and precision alignment are more effective.

Welcome to the world of a 2 cylinder diesel engine. The 3YM30 on my J/109 is much smoother at all rpms.

Ah yes - buy a bigger boat! That thought has occurred to me more than once, but I can't seem to find a better boat for the money that offers the racing and cruising potential of the J30 - even though compromised on both scores. I will keep searching, but in the meantime I am stuck with messing around in an old boat.
Thanks for all the info you have shared and continue to provide - a truly valuable resource to this community.