Shaft coupling question.

[DougM]

There is probably a good reason, but I have always wondered....
Since engine to shaft alignment seems to be a fairly regular maintenance issue, and it's necessary to disconnect occasionally, why are either universal joints or CV joints not used ( other than cost)? It would seem that that type of connection would compensate for some misalignment.

 

[whatfiero]

Shaft couplings

If cv or flexible coupling used you would need another bearing to support drive shaft. And you only need to adjust if it's knocking or wearing on packing , drip less seal. If your concerned tie boat up good at dock expose coupling start engine put in gear run at different speeds and check if it wobbles around a lot only then it needs adjusting , a lot of info on sight how to do.

 

[kloudie1]

such things as flex couplings do exist and some are used on some of the high end boats,
http://search.defender.com/?expression=shaft coupling&s=1&Trigger=ac
CV joints like in cars aren't good at taking thrust so would require a thrust bearing. Universal joints (common drive shaft ones) have a "snap-over" where their speed transmitted is not constant all around the motion circle. They should be set in offset pairs so that the motion changes cancel out .. Can be done. certainly, but pretty expensive to put in correctly. The constraint of engine location doesn't easily allow for a long powertrain. One of the outstanding benefits of a saildrive is that the alignment thing goes away.. They have some other maybe more onerous problems, but alignment is not one of 'em.
EDIT: Note that the Globe folks still call for an alignment to .005" out, max, before installing..