There’s the rub as I see it---the lovejoy, in allowing some misalignment would allow the unsupported upper end of the driveshaft to deflect, compressing the lovejoy, further causing “mass imbalance”, leading to cyclic vibrations at the power head---not a good thing. Further, this would pretty much happen as function of speed, not load. Mass imbalance isn’t fun…when trying to machine/adapt a 14”diam conical bore prop to the straight bore/shear pin needed for my outboard prop shaft, we didn’t take the time to ensure that the resulting straight bored hole was concentric with the original conical bore. This caused a slight mass imbalance and possibly some angular wobble offset. The prop would work fine, but with speed, cyclic vibration was more than noticeable, it was unsettling as I feared the lower unit bearings our housing might become compromised. We were more careful with the next prop we modified.
For those of you who know the sound and feel of a carrier bearing or u-joint going out on our car, a poorly supported upper end of an outboard driveshaft would be similar.
-mt
From: electricboats@
Sent: Wednesday, December 30, 2009 10:14 PM
To: electricboats@
Subject: [Electric Boats] Re: Source for coupler (14 spline, 5/8ths shaft) to motor or pully
????
I am totally puzzled for two reasons;
1. I have been the owner of many of the millions of boats with the prop shaft hard connected to the motor. 0.0005 per inch of coupling face is the standard alignment spec. This is the same spec for aligning electric motors in industrial applications. Lovejoy and other couplings are for low hp applications and to minimize shock load. You line up a LoveJoy exactly the same way, before installing the rubber cross.
2. This is an OUTBOARD MOTOR the fellow is connecting to so what does the flex of the hull have to do with the coupling?
--- In electricboats@
>
> Myles, The "guarantee" is the splendid bit of engineering you do that calculated the shear values. The fellow wanted to avoid welding and machining, which is why I came up with this solution.
>
> When I said "buy a coupler" I meant one of the many types that allow movement and misalignment like a Lovejoy connector. Prop shafts should never be hard connected to motors, especially in boats because the boat itself can flex, causing excessive force on the motor bearings.
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