To bond or isolate

[Spyro]

Old set up on the boat was the Battery Negative was connected to the engine block and so to the gearbox, coupling and propshaft. Thus earthing the whole dc negative side (when in the water)
I have fitted an R&D flexi coupling and have bridged the coupling electrically thus to keep the DC -ve earthed through the shaft.
What difference would it make if I had isolated the shaft and prop from the negative side. I know all my electrics would still operate ok because they do when the boat is on the hard but does it make a differnce to a shaft anode etc or corrosion on the prop. Would my shaft anode or engine anodes last longer if it was isolated?

 

[SHUG]

Aaah that old chestnut. To bond or not to bond ,that is the question!!!!

My own thinking was not to bond the bronze (Blakes) seacocks and to make the prop shaft look like a lower order metal by putting on two shaft anodes. Seemed to work over a six year period.No pink
anywhere.

PS I have just spotted a related post just four after you.

 

[Tranona]

The purpose of bridging the coupling is to complete the bonding of your anode to the stern gear. This assumes you have the bonding wire to the gearbox casing or bell housing bolts. It does not affect the electric of the boat. If you do not have a hull anode but are relying on shaft anodes, then no need for the bridge.

 

[Spyro]

The purpose of bridging the coupling is to complete the bonding of your anode to the stern gear. This assumes you have the bonding wire to the gearbox casing or bell housing bolts. It does not affect the electric of the boat. If you do not have a hull anode but are relying on shaft anodes, then no need for the bridge.

No hull anode just a shaft anode but if I don't have the bridge do I need some sort of earth strap or another way of earthing the engine block and neg side of the battery?

 

[vyv_cox]

I don't believe the concept of 'earth' applies with a 12 volt DC system. It may be a convenient way of arranging the negative return, but nothing else. Cars have traditionally used the chassis/body as a negative return but there is no 'earth'. Saildrives are electrically isolated from the engine and everything else, so no part of the boat is 'earthed'.

 

[Clyde_Wanderer]

I would have thought there was no need for 12v electrics to be earthed to any hull fitting or shaft/prop etc as it has its own -v return system.
I was under the impression that bonding was when hull fittings and propshaft were connected to the hull annode by way of a bond wire, is this correct?
On my boat there is one pear annode on the hull up a foot or so from the skeg, this has a cable from one of its mounting bolts connected to the engine/gearbox but no cables/wires to any of the hull/skin fittings, is this adequete?
The only thing I got some slight corrosion on is the prop but I am going to fit a bridging cable across the coupling as Spyro has done.
Is this arrangement adequete?
Someone educate me.
C_W

 

[VicS]

I would have thought there was no need for 12v electrics to be earthed to any hull fitting or shaft/prop etc as it has its own -v return system.
I was under the impression that bonding was when hull fittings and propshaft were connected to the hull annode by way of a bond wire, is this correct?
On my boat there is one pear annode on the hull up a foot or so from the skeg, this has a cable from one of its mounting bolts connected to the engine/gearbox but no cables/wires to any of the hull/skin fittings, is this adequete?
The only thing I got some slight corrosion on is the prop but I am going to fit a bridging cable across the coupling as Spyro has done.
Is this arrangement adequete?
Someone educate me.
C_W

There must be a good low resistance path between the hull anode and the item(s) it is fitted to protect. If the anode is connected to the engine/gearbox then any flexible shaft coupling must be bridged in order for that path to be complete. .......
Continuity through the gear box internals and the bearings may not always be good however. That is the reason why sometimes it is necessary instead to fit a brush assembly ( eg MG Duff's "Electro eliminator") that makes direct contact with the shaft immediately inboard of the stern gland.

Do not connect non ferrous through hulls to the same anode

Do not connect the DC negative to the through hulls

 

[Clyde_Wanderer]

There must be a good low resistance path between the hull anode and the item(s) it is fitted to protect. If the anode is connected to the engine/gearbox then any flexible shaft coupling must be bridged in order for that path to be complete. .......
Continuity through the gear box internals and the bearings may not always be good however. That is the reason why sometimes it is necessary instead to fit a brush assembly ( eg MG Duff's "Electro eliminator") that makes direct contact with the shaft immediately inboard of the stern gland.

Do not connect non ferrous through hulls to the same anode

Do not connect the DC negative to the through hulls

Thanks for that Vic.
I had searched for an old Haverhill petrol welder/generator to salvage the spring loaded brush holders from and make a electro eliminator, as the MG Duff system is almost identical but 10 times the price, but I couldent get hold of one.
What would you regard as Non Ferrous through hulls? do you mean Bronze, s/steel, DZR brass?
Thanks, C_W

 

[VicS]

What would you regard as Non Ferrous through hulls? do you mean Bronze, s/steel, DZR brass?
Thanks, C_W

Bronze, gunmetal and DZR obviously but I think I would also include stainless steel...........and plastic

 

[Clyde_Wanderer]

Bronze, gunmetal and DZR obviously but I think I would also include stainless steel...........and plastic

Vic, All the 12v system -v battery and alternator -v cables are connected to a terminal which is secured to one of the engine mounts, bearing in mind the engine is also connected to the hull annode with a bonding cable, would this create any problems?
Thanks, C_W

 

[VicS]

Vic, All the 12v system -v battery and alternator -v cables are connected to a terminal which is secured to one of the engine mounts, bearing in mind the engine is also connected to the hull annode with a bonding cable, would this create any problems?
Thanks, C_W

Not if I understand you correctly.

What you should avoid is any cable being used for bonding the anodes also being used for carrying current.

 

[Billjratt]

Using a multimeter on the millivolt scale, you can detect future problems by measuring between the components you have mentioned. Any that are immersed and have a voltage between them will react. (Short them out with bonding)
None of my boats have had a bonding system. Shaft anodes have been a good solution - the current(!) boat has a 'pear' on the hull which is difficult to keep bonded to the shaft. The engine and everything else is isolated and has been since 1978 - successfully. I always hang an anode over the side near the prop when in marinas .
Remember, if an anode doesn't deplete, it probably isn't working properly. My isolated engine doesn't have any internal anodes to monitor/replace either.

 

[GrahamM376]

There must be a good low resistance path between the hull anode and the item(s) it is fitted to protect. If the anode is connected to the engine/gearbox then any flexible shaft coupling must be bridged in order for that path to be complete. .......
Continuity through the gear box internals and the bearings may not always be good however. That is the reason why sometimes it is necessary instead to fit a brush assembly ( eg MG Duff's "Electro eliminator") that makes direct contact with the shaft immediately inboard of the stern gland.

Do not connect non ferrous through hulls to the same anode

Do not connect the DC negative to the through hulls

+1

 

[Spyro]

Using a multimeter on the millivolt scale, you can detect future problems by measuring between the components you have mentioned. Any that are immersed and have a voltage between them will react. (Short them out with bonding)
None of my boats have had a bonding system. Shaft anodes have been a good solution - the current(!) boat has a 'pear' on the hull which is difficult to keep bonded to the shaft. The engine and everything else is isolated and has been since 1978 - successfully. I always hang an anode over the side near the prop when in marinas .
Remember, if an anode doesn't deplete, it probably isn't working properly. My isolated engine doesn't have any internal anodes to monitor/replace either.

Bill
Re' engine being isolated. Is this not difficult to achieve assuming you have water in the cooling system. The engine block will be connected to -ve side of the batteries via starter motor and alternator housing so the engine will be earthed via the water in the cooling system.

 

[jfkal]

What god has seperated man should not combine

Old set up on the boat was the Battery Negative was connected to the engine block and so to the gearbox, coupling and propshaft. Thus earthing the whole dc negative side (when in the water)
I have fitted an R&D flexi coupling and have bridged the coupling electrically thus to keep the DC -ve earthed through the shaft.
What difference would it make if I had isolated the shaft and prop from the negative side. I know all my electrics would still operate ok because they do when the boat is on the hard but does it make a differnce to a shaft anode etc or corrosion on the prop. Would my shaft anode or engine anodes last longer if it was isolated?

Well that is only my experience. Removed all bonding wires and never has a problem ever since (+10 years).