Unusual flex coupling, engine to trans, video

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sdowney717

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MSN https://www.msn.com/en-us/weather/topstories/double-power-installing-a-main-engine-and-spare-engine-in-a-wooden-boat-for-ultimate-performance/vi-AA1IUOyb?ocid=msedgntp&pc=U162&cvid=ce379429da6043dcf956e3bf13b3cebd&ei=54
 
Wow! Keep the engine cover on that one. Good chance of vibrations, and if it let go it could destroy the engine bay. Could make a spare out of old rubber conveyor belt though.
 
Wooden boats need very high compliance couplings if the engine isn't handling the thrust. You can use really soft engine mounts this way - very important on old wooden boats not to shake the caulk out of them or fret the planking. I've seen 4" fire hose used this way. Small tires also - but I wouldn't use them on a boat because of the fire risk.
 
I think for them with the small engine it works well and keeps everything from vibrating.
A small strong rubber tire could work, if you could get the bolts in and relatively inline, otherwise it will be like an out of balance car tire spinning.

Even the transmission has a U joint couple, all the motor does it provide torque.
I have seen more videos with that U joint couple to a transmission.
Why is this not used more ?
It seems ideal, not a big deal if the coupling alignment is not perfect.
Can it not handle the larger horsepower of bigger engines?
Maybe it could if properly sized joint was used.
 
The tranny is pushing the boat, not the engine. Wooden boats have substantial global flex issues and you want the thrust block rigid and as close to the gland as possible so there isn't too much motion at the gland. Once you have gotten the thrust load off the engine, and the bell housing torque load as well, the engine mounts have a lot less to deal with and you can soften up the mounts by a lot. So the tranny mounts really have all the thrust and torque to cope with, and any prop vibrations, but can be isolated from engine wind, engine vibrations, torque ripple, and global bending of the hull. This is simply best practice on wooden boats.
 
seasquirt said:
Wow! Keep the engine cover on that one. Good chance of vibrations, and if it let go it could destroy the engine bay. Could make a spare out of old rubber conveyor belt though.
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That band is pretty light weight, meaning less weight to throw itself around if unbalanced.
Could also attach a weight on the inside of the band if you could determine which side is unbalanced
 
It might be light, but how light is a whipper snipper cord, and cord trimmers can do a lot of damage.
 
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