Electrical continuity over flexible coupling

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DavidMcMullan

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What is the best retrofit method to get electrical continuity across a flexible coupling, for a boat afloat?
Possible options are:
- a cable between 2 bolts on coupling
- a copper strip between 2 bolts on coupling
- R&D Marine do a roll-up strip, but that should be installed before installation of coupling
- MG Duff have an electro elimator, with brushes on shaft connected to earth (±£67 /forums/images/graemlins/shocked.gif).
Any others?
 
I`ve used copper wire to bridge the coupling before with no probs. However, it`s worth casting a wary eye over it now and then, provided its easily visible of course, as like anything else, it can break.
 
I had two earthing braid strips made up with ring ends to match the coupling bolts. These are cross linked fore and aft across the coupling. Solid copper strips will be subject to slight bending, work annealing and fatigue if the coupling is actually doing what its supposed to. At approx 1000 rpm I wasn't worried so much about balance so much as redundancy /forums/images/graemlins/smile.gif
 
If you find that some wire across two bolts keeps breaking (or the connectors do) then you could use thicker battery wire, using a more substantial battery crimped connector at one end, and at the other clamp it to the shaft using a hose clip.
 
I used a copper strip the first year after installing my new diesel, but have reverted to the braided strips. I find they last two to three years before needing to be replaced.
 
Could someone please explain what the main benefit is of such a connection? I have a fairly new engine installed, with an R&D flex coupling, but I choose to leave the shaft and prop "isolated" from the engine, – just as the seacocks are not electrically connected to anything. Anode on the prop, though. What risk do I run?
 
I found that copper wiring breaks up across the coupler. So I now use monel shackle seizing wire - it is springy and stays bright. Looped around a couple of the bolt heads on opposite ends of the coupling it has stayed put for a couple of years. I now can use a hanging anode instead of a shaft anode to protect the prop - buy the cheapest lump of zinc rather than the one that has to fit...
 
I went to the local pound shop and brought a squids worth (3) "stainless" pot scourers ~ break them open and tease some stainless wire out ~ split the coupling and bung the middle of the R&D coupling full of the stuff ~ bolt the coupling back up and you'll find that you have continuity on the shaft.

1 scourer should do you for about 10 years!!!

Peter.
 
Hi Babayaga, I too have a fairly new engine installation and the engineer fitted a heavy wire between the shaft, over the flexible coupling to the engine. I told him I didn't have it before on the old Volvo so why did I need it now. He told me his belief was that it was necessary but couldn't explain exactly why. I removed it. Nothing on my boat is bonded (Contest 36k) I had a new prop and prop shaft and the old ones had no corrosion at all. My DC earth is not connected to my AC earth either. I read and read about this and because there is a split in the wisdom of bonded or unbonded it's hard to get a feel for what is the right way. I figure that if nothing is bonded things are simpler and the evidence of my boat is that it works as there is no corrosion. I also have an anode on the propshaft but my new propellor is a Kiwiprop which is stainless and plastic (nytol). The anode is in place for a second year now without changing. After all my reading I am non the wiser but all I know is if everything else is unbonded I don't want my propshaft bonded to my engine and hence to the rest of my DC circuit. So, sorry I can't answer your question but your in good company!
 
Mine has no anode on the shaft, and no space to put one. Only way of getting a bond is via the shaft on the inboard side (such as shaft brushes) or via the engine.

First year the bond broke and I did not notice till the end of the season, by which time the prop was a touch pink.
 
As above, I installed a R&D with a new engine, only because the engine was slightly shorter than the old one. Forgot about the bonding, after two years the prop dezinced enough that it cannot be repaired next time I dink it. I used a piece of 15mm water pipe , flattened and drilled, on two bolts around the outside edge, later replaced with a centre bolt between the two metal straps.
 
Same here - on my Volvo installation the gearbox is electrically isolated from the engine (which is bonded DC & AC earth to a hull anode) with dire warnings in the handbook not to breach the isolation. Consequently I see no point in bonding the R&D flex coupling either.

I don't believe there is a definitive answer and each individual installation has it's own requirements.
 
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