Federal Flexible Coupler: Opinions?

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In replacing my transmission, I have to be cognizant of the space between the stern tube and new transmission.  I'm losing 4mm of that space due to the new transmission (Twin Disc/TMC 40P).  I also went with a PSS dripless two years ago when I replaced my prop shaft.

Some sort of flexible coupler is recommended.  Presently, I just have a basic split/rigid coupler.  It looks like the Federal 43A flexible coupler would be a good application here due to its compact size.  I know several owners have installed them.

Has anyone had a bad experience with one of these?  I'm told they are a pretty old school design--which is not a bad thing at all.  I'm hoping it would be the right application here and would appreciate any input.   Again, going to a Bullflex (or other model) flexible coupler looks like it will increase the overhang (of the prop shaft aft of the P strut) too far.




I put one in about 6 months ago, so I don't have a lot of hours on it. I will say it made a noticeable improvement to the smoothness while motoring.

The one hesitation I would have in recommending it is that you are not suppose to align the motor with it in place, you're suppose to swap out the coupler with a solid coupler to do the alignment and then reinstall the flexible coupler. And of course you're suppose to do the engine alignment while the boat's in the water.

I don't see that I would be able to back the prop shaft off the flexible coupler enough to remove the coupler and still have enough prop shaft sticking out of the stuffing box to be able to grab and pull it back up. So I think I'd have to dive under the boat to push the prop back up the stuffing box.


1998 Catalina 34 Mkii 1390 - Miss Allie
New Bern, NC

Ron Hill

Patches : You didn't identity your hull #.  I had a Bulflex on my M25XP engine.  If you have a ZF 10 (or Hurth 100), you'll run out of space between the transmission and the packing gland!!  When I changed to a M25XPB engine I went with a Federal and it works just fine!!

A few thoughts
Ron, Apache #788

Bill Shreeves

I too installed a Federal Flexible coupling with a ZF10 on my M25XPB back in 2017.  Its served me well and reduced vibration.
The only thing that always works on an old boat is the owner...

Bill Shreeves
s/v "Begnnings" 1987 Shoal Draft #333
M25XPB, Worton Creek, MD