Electrical bonding on stern tube

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Plevier

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On my Jeanneau the stern tube is maybe 3" long with a flange on the outside of the boat and a Volvo seal on the inside end. It's held in by 2 studs on the back of the flange with nuts inside the boat.

On one of these studs there is an electrical bonding lead. It's heavy, 10 sq mm. It's original, it's shown on the 12V circuit diagram in the boat manual and it's shown linked to the alternator ground with a 6 sq mm wire from there to the fuel tank and a 2.5 sq mm from the fuel tank to the filler cap.

The 230V wiring diagram shows the mains earth going to a tie point on the distribution board but isn't specific about anything further. I don't know if the 12V bonding lead (which is green/yellow) is linked to mains earth, I will check next time at the boat.

There is no hull anode, only a prop shaft anode, and none of the other skin fittings is bonded. The engine is a Volvo and the gearbox and shaft are electrically isolated from the engine and Volve stress they should not be bridged.

So what on earth is this bonding wire for? I can only see it discharging any static from the fuel filler, I'm used to putting an earth lead on when fuelling aircraft but you don't normally worry with diesel boats do you? My boat is lift keel and I often fuel from cans when dried out so that would defeat this anyway!

Any other ideas please? :confused:

Here's the inside (from someone else's same model of boat done exactly the same)

View attachment 27640

and here's the flange outside (that's a wooden bung in it not the prop shaft - pic taken to show excessive grit blasting)

View attachment 27639
 
It could be that the bonding path to an anode is via the engine / shaft. I have to say I wouldn't be happy about that and would prefer a hull anode that isn't so prone to falling off as one on the shaft. Easy enough to fit a hull anode and you can then have 2 bonding routes to an anode. Having seen the speed that damage occurs when you loose an anode it has to be worth considering a fixed anode.

yoda
 
But bonding to the stern tube won't do any good for the prop as it is not connected to the prop electrically - even if there were an anode on the other end of that wire.
 
Thanks but as I said the shaft is insulated from the engine so no connection to anode that way.
If they think this small bronze fitting needs wiring to a hull anode then why don't they fit one and what about the other skin fittings?
Also this is a much heavier wire than normally used for anode circuits.
Sorry but I don't think that's cracked it!
 
Troubadour said:
On my Jeanneau the stern tube is maybe 3" long with a flange on the outside of the boat and a Volvo seal on the inside end. It's held in by 2 studs on the back of the flange with nuts inside the boat.

On one of these studs there is an electrical bonding lead. It's heavy, 10 sq mm. It's original, it's shown on the 12V circuit diagram in the boat manual and it's shown linked to the alternator ground with a 6 sq mm wire from there to the fuel tank and a 2.5 sq mm from the fuel tank to the filler cap.

There is no hull anode, only a prop shaft anode, and none of the other skin fittings is bonded. The engine is a Volvo and the gearbox and shaft are electrically isolated from the engine and Volve stress they should not be bridged.

So what on earth is this bonding wire for?
Click to expand...

Is it a bronze stern tube? Our bronze stern gland has a bonding wire but our tube is grp.

Skin fittings shouldn't be bonded, that's asking for trouble. I'm puzzled though that your boat doesn't have a hull anode, which is normal practice. Also, that the engine/gearbox/shaft shouldn't be connected - I could understand it if a sail drive was fitted but not with a standard shaft setup, is the gearbox case alloy?
 
GrahamM376 said:
Is it a bronze stern tube? Our bronze stern gland has a bonding wire but our tube is grp.

Skin fittings shouldn't be bonded, that's asking for trouble. I'm puzzled though that your boat doesn't have a hull anode, which is normal practice. Also, that the engine/gearbox/shaft shouldn't be connected - I could understand it if a sail drive was fitted but not with a standard shaft setup, is the gearbox case alloy?
Click to expand...

The OP says that the stern gear is protected by a shaft anode. ..

What would a hull anode be fitted to protect ? What underwater parts would you bond to it ?
 
Troubadour said:
The 230V wiring diagram shows the mains earth going to a tie point on the distribution board but isn't specific about anything further. I don't know if the 12V bonding lead (which is green/yellow) is linked to mains earth, I will check next time at the boat.
Click to expand...

If the shore power ground is connected to the 12VDC negative it could be a way to connect your mains earth to the sea water/ ground.
 
VicS said:
The OP says that the stern gear is protected by a shaft anode. ..

What would a hull anode be fitted to protect ? What underwater parts would you bond to it ?
Click to expand...

My shaft is also protected by shaft anode and the prop has its own as well. In addition, the shaft flexible coupling has a wire bridge.

Connected to my anode (presumably fom new) are - bronze stern gland, rudder stock/quadrant, engine, fuel tank & filler. The standard half pear shape hull anode lasts 2 seasons usually, the shaft one 2 years but the smaller prop only 1, indicating all are working.

Without the hull anode taking some of the strain, I suspect the prop anode would not last a season, as a mate found - his only lasted around 6 months so he fitted one of these - http://www.mgduff.co.uk/mgduff-product-catalog/Electro+Eliminators/ - it cured the problem.
 
GrahamM376 said:
My shaft is also protected by shaft anode and the prop has its own as well. In addition, the shaft flexible coupling has a wire bridge.

Connected to my anode (presumably fom new) are - bronze stern gland, rudder stock/quadrant, engine, fuel tank & filler. The standard half pear shape hull anode lasts 2 seasons usually, the shaft one 2 years but the smaller prop only 1, indicating all are working.

Without the hull anode taking some of the strain, I suspect the prop anode would not last a season, as a mate found - his only lasted around 6 months so he fitted one of these - http://www.mgduff.co.uk/mgduff-product-catalog/Electro+Eliminators/ - it cured the problem.
Click to expand...

Volvo stress that the gearbox and thus the shaft (and it's a solid coupling) are isolated and should remain so, nothing should be fitted that bridges the insulation.
It's debatable whether I need a shaft anode at all - it's a 316 shaft and a Kiwiprop that has 316 metal parts and plastic blades.
Interesting that your fuel tank and filler are connected to the anode. I think the object must be to earth it as I am guessing with mine.
 
GrahamM376 said:
Is it a bronze stern tube? Our bronze stern gland has a bonding wire but our tube is grp.

Skin fittings shouldn't be bonded, that's asking for trouble. I'm puzzled though that your boat doesn't have a hull anode, which is normal practice. Also, that the engine/gearbox/shaft shouldn't be connected - I could understand it if a sail drive was fitted but not with a standard shaft setup, is the gearbox case alloy?
Click to expand...

Have a look at the pics - it's just this one piece about 3" long, there isn't really a stern tube. The shaft passes through the hull then is exposed to a P bracket.
If I had a hull anode I'm not sure what I could protect with it. As you say, not the skin fittings. Not the shaft and prop (see my other reply to you). Only leaves the keel - 1400kg of cast iron epoxy coated. The swing blade - 80kg of steel plate - could do with protection, as new it's galvanised but that soon goes, but it needs anodes on it not a hull anode.
 
Troubadour said:
So what on earth is this bonding wire for? I can only see it discharging any static from the fuel filler, I'm used to putting an earth lead on when fuelling aircraft but you don't normally worry with diesel boats do you? My boat is lift keel and I often fuel from cans when dried out so that would defeat this anyway!

Any other ideas please? :confused:
Click to expand...

I'd imagine your Jeanneau is built to CE standard and has the shorepower earth connected to the 12v earth. Normally, this will allow a path to earth (the water) through the propshaft, to ensure that your boat's RCD will trip in a fault condition. In your case, the shaft is electrically isolated from the engine, and so presumably Jeanneau have used the stern tube as a convenient connection for earthing.
 
pvb said:
I'd imagine your Jeanneau is built to CE standard and has the shorepower earth connected to the 12v earth. Normally, this will allow a path to earth (the water) through the propshaft, to ensure that your boat's RCD will trip in a fault condition. In your case, the shaft is electrically isolated from the engine, and so presumably Jeanneau have used the stern tube as a convenient connection for earthing.
Click to expand...

That's a good thought, CE requirements, and would explain the 10 sq mm cable. I'll have a look tmrw if there is a 10 sq mm bond from there to mains earth.
 
Troubadour said:
Yes it is bonded to the mains earth. I think pvb has won the coconut. Thanks.
Click to expand...

I dont see the logic in connecting the shorepower earth to the water :confused:

Are you suggesting that the boat is earthed via the stern tube and the water rather than with an earth conductor in the shorepower supply
 
Last edited:
VicS said:
I dont see the logic in connecting the shorepower earth to the water :confused:

Are you suggesting that the boat is earthed via the stern tube and the water rather than with an earth conductor in the shorepower supply
Click to expand...

No, but in the event of a lost earth on the shore supply in some dodgy boatyard - or connecting to a 2 wire supply somewhere - and an earth fault occurring on the boat it provides a leakage route to trip the RCD.
Although I don't live out in the sticks, I only have a 2 wire supply with no earth at home. It's not uncommon. My safety depends on an RCD and an earth rod.
As I jokingly said earlier, you could look on this as a marine earth rod.
I suppose when I take advantage of my lift keel to dry out, I should nip over the side and stick an earth rod in :)
 
Troubadour said:
No, but in the event of a lost earth on the shore supply in some dodgy boatyard - or connecting to a 2 wire supply somewhere - and an earth fault occurring on the boat it provides a leakage route to trip the RCD.
Although I don't live out in the sticks, I only have a 2 wire supply with no earth at home. It's not uncommon. My safety depends on an RCD and an earth rod.
As I jokingly said earlier, you could look on this as a marine earth rod.
I suppose when I take advantage of my lift keel to dry out, I should nip over the side and stick an earth rod in :)
Click to expand...

So what would you do with a GRP hull and a saildrive ? Fit a ground plate? There is no mention of doing that AFAIR in ISO 13297. If its a European requirement then I guess it will be also in the new edition of ISO 13297 ??
 
VicS said:
So what would you do with a GRP hull and a saildrive ? Fit a ground plate? There is no mention of doing that AFAIR in ISO 13297. If its a European requirement then I guess it will be also in the new edition of ISO 13297 ??
Click to expand...

I don't know.
Do you have a better explanation for my bonding connection?
 
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