PYI Flexible Coupling & Prop Overhang?

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newgringo

Member III
I was just about ready to install a PYI 910001 Flexible Coupling on the M-25 in our E32-3 and started reading the posts on this site. I am just not sure about sliding the shaft back another 1.28 inches. I would still have enough room to repack the stuffing box but having the prop back furthur concerns me. Right now the forward edge of the prop hub is 4 inches aft of the strut, which already seems like a lot. It would end up 5 1/4 inches aft with the coupling installed. This also puts the prop closer to the rudder, which now 5 inches from the shaft tip to rudder leading edge. We are not planning to haul the boat for a while so shortening the shaft is not a present option. Right now with our new 3 blade prop, vibration is pretty low and is mainly engine induced. Just thought a coupling might be a quick easy way to make it even smoother and possibly extend the life of bearings and things.
Some advice would be greatly appreciated.
Jerry in Kingston, WA
 
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jeff_mc

Member I
id dont know about the clearances but pulling the shaft in the water isnt a problem. during my recent repower, i pulled it several times. you need a couple of shopping bags and a wax toilet ring. remove the coupler (could be a problem if its been on there for years). tie off the prop and shaft, so it doesnt plummet into the abyss. stuff a bag in the stern tube, followed by copious ammounts of wax, then another bag. reverse the process for the install. you should have someone onboard to recieve the shaft and water. i always keep at least one wax ring on the boat just in case.
 
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cawinter

Member III
Not sure if I can add any more than I put into my drive train rebuild post from some time ago. 4"+ seems very far. The (reputable) prop/shaft shop that I used to get a new AQ shaft, suggested around 1-2 times the shaft diameter. They said it was not critical since we don't have a lot of torque. Then again I am not sure what they would say about 5"+

After the rebuild my spece is very tight but the PTFE stuffing has held up very well last year. I will regrease but to date I still have to see more than a few drops come out (even with the nut just barely tightened). The PTFE is great.
 
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newgringo

Member III
After reading your "drive train rebuild post " and considering your comment above I think I will hold off on installing a coupling. My past life as a mechanical engineer says 5+ inches overhang on a 1 inch shaft behind a pretty deep strut is not sound stiff engineering. When I have to pull and shorten the shaft and replace the stuffing box it will be time for this upgrade. In the meantime there a list of other chores. Thanks - Jerry
 
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cawinter

Member III
Probably a good decision. The costs for everything really didn't amount to much on the boat scale, and you might as well go all the way and then forget about it.

Good luck!
 
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