Tartan 27' owner
Join Date: Jan 2008
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Re: Lengthening the prop shaft
You are correct and observant. The Drive Saver does isolate the shaft from the motor electrically speaking. I believe that the Drive Saver website mentions this as if it were a benefit and feature of their gizmo. I'm not sure that I buy that either.
I don' have a Masters in EE, nor am I a naval architect but I also like the idea that the engine is connected to the water via the shaft and prop in the event of a lightning strike. Then again, with lightning carrying around 10 Zillion volts it can surely jump, or arc through an inch or so of air on it's way to an eventual ground.
They claim that the DS prevents electrolysis by separating the engine from the shaft but it is usually the prop (bronze) that seems to bear the worst of it rather than the engine block. I think that the shaft zinc is more to protect my prop than my engine and replacing a zinc (< $20) is a lot cheaper than replacing a prop.
My plan (never implemented) was to run some wire(s) from the bolt heads on the shaft coupling side of the DS to the bolt heads on the output flange, thus connecting both sides electrically. I'd ask your friends at Marshall Marine what they thought about this issue.
Copacabana's idea about having a metal spacer (say 1/2" - 3/4") made of metal would leave everything electrically connected. I'd speak to a prop shop about this as the fabrication process would have to be pretty rigorous. As you know, you need a very close tolerance (+/- .001" or something) for the mating surface between the shaft coupling and the output flange. I'm not sure what a prop shop would charge for making you a custom metal spacer. Would it be more than an "out of the box" Drive Saver? I just don't know.
"The cure for anything is salt water~ sweat, tears, or the sea." ~Isak Denesen
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