To Bond or Not to Bond That is the Question

[Golden Echo]

Have a SS prop shaft, bronze prop, and prop coupler is connected to a plastic drive saver which in essence isolates the prop shaft from ground. I've heard I should have the shaft bonded to reduce electrolysis. If this is so can I simply take a wire and connect the prop hub bolts to the trans hub bolts therefore electrically connecting the engine to the prop shaft? Wisdom needed. Thanks!

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[Boatyarddog]

Yes, in theory that would now connect the prop and related hard ware to the engine -neg dc circuit.
However, bonding these components needs careful consideration,if using a SSB, you'll want to install a sinter plate under the hull.
If not, use those fore mentioned prop and shaft zincs, and see how long they last, this period will vary along with different conditions of sail, or motoring.


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[colemj]

I think bonding an isolated shaft/prop will increase electrolysis, not decrease it. Impressed currents will be on your DC system, so connecting something that was previously isolated will bring it into play. The shaft zinc should handle any galvanic current.

Mark

[Boatyarddog]

It's good to consider if you've had any issues with pitting or degrading of the prop, or shaft.
Don't just bond because someone told you to .
There are reasons for doing this.


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[sailorboy1]

I read the same question in a magazine and Nigel calder's answer was that the science was murky either way far as leaving the shaft unbonded/bonded. So if it was my boat I would leave it whichever way it currently is.

[goboatingnow]

In a grp boat. Don't bond and don't connect AC protective earth to negative DC. ( despite what ABYC day )

Fit a whole boat RCD ( ELCI )

Dave

[colemj]

Originally Posted by goboatingnow

In a grp boat. Don't bond and don't connect AC protective earth to negative DC. ( despite what ABYC day )

Fit a whole boat RCD ( ELCI )

Dave

Even doing all of that, he still has the question about bonding his currently isolated shaft and prop.

A similar example is the Volvo saildrive, which is electrically isolated from the engine -and thus the rest of the boat. The zinc on the saildrive takes care of any galvanic issues with dissimilar metals (bronze prop, SS shaft, Al housing), but the isolation is what protects the drive from electrolysis.

But to answer the OP's question - if you do want to rebond the shaft and prop to the engine and DC system on the boat, then yes, a wire or strap jumped across the coupling junction will do so.

Mark