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Old 11-17-2015, 12:33 PM   #10
R_p_ryan
Senior Member
 
City: San Francisco
Vessel Name: Shellbourne
Vessel Model: 1978 Mainship 34 Perkins T6.354
Join Date: Dec 2014
Posts: 171
I don't know. If you're more inclined to keep everything stock then bailout of the below.

I would get creative, especially if I had two engines - but only because I am cheap and enjoy solving these types of problems. Certainly risk is a big consideration here, as this is a critical component. Failure of the coupling wouldn't render you immediately without an engine but you would only have a small amount of time before you must shut down or suffer damage/failure. Lets say you don't have Murphy gauges, have only a single engine, and commonly transit a bar or other dangerous waters. In this case I wouldn't waver far from the stock solution. However, let's say you have an alarm on your raw water flow, have two engines, and stay within calm waters where you can almost always just anchor and call for Vessel Assist. Then I would feel more license to come up with a coupling that is farther away from a stock solution.

Let's say you're in the latter of those two groups, since if you're in the first group you need stay with the stock solution.

I have the same water pump setup on my mainship so I have some context. I believe the purpose of this coupler is to allow for some axial play between the water pump and the PTO shaft. This is a common problem in machinery. The Perkins solution is certainly tried and proven, however there are likely alternatives. The interface between a PTO shaft and a power consuming device, such as a water pump for a marine diesel, or a fertilizer spreader for a tractor diesel, are similar. There are hundreds of different types of couplers that allow for alignment and play between two shafts. The specs would be the shaft diameters, keyway size, RPMs, torque, tolerance, etc.

I don't know what the torque on a water pump shaft is. Here are some shaft couplings in the $50 - $250 range with ratings between 140 and 3700 in-pounds.

McMaster Carr offers these:
McMaster-Carr
McMaster-Carr

If you're not comfortable or have any concerns then stick with the stock - it's tried and proven. These might work, but like I said earlier, I don't know.
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