earthing to ally hull!?!?

[therapy]

Gedday ausfishers. I've had a few problems with earth's of late and a good mate has fixed some of these and said he will pretty much rewire the whole boat for me for the cost of a bottle of Bundy. All good except that the new earth he has run from the back of some switches is to the hull of the boat, the boat being a 5mm plate ally hull. Another bloke at work said a mate of his had alot of trouble with electrolisis because he had earthed to his hull. I don't know too much about all this myself but would appreciate any advice... Thanks in advance
Cheers ...... Terry..............

[littlejim]

Can't speak about an alloy boat, mine is F/G so earth is always a wire. But years ago I owned a pommy caravan in the UK which used the aluminium exterior for earth. The copper wire aluminium connection always corroded after a few months. I could tell when the time came to scrape it back to bare metal again, by the weird reactions my fellow motorists produced when I put a turn flicker on. When the connection was corroded the current used to try to get to earth through every light on the van. Whichever one I put on, flicker, park, stop, the whole thing lit up like a Christmas tree and everyone had to take a guess at what I was trying to say.
In your situation I would give it a big miss. (Suspect it would give galvanic corrosion a big boost in the water too.)

[BLOOEY]

As far as i am aware you do not earth tinnys. You're pretty much making a big battery out of your boat. Ben

[Mark-P]

Never earth to an Aluminium boat !!! Your just asking for drama's......
Earth straight to the battery only !!!

Mark

[fivefishes]

Mark,

Thanks, i just re-wired my tinny, thought some of the above suggestions might be an issue so straight to the battery, good to have that confirmed.

Matt

[frank100]

Therapy,
Definite NN NO to use the hull as an earth or common. Electrolysis on the wires where attached to hull for a start, the copper wire will corrode off & "eat" a hole in the ally. To fix remove any wires terminated to the hull. The only connection to the hull should be the motor common, as long as this is the only connection there should be no current flow through the hull ( or any part of it). Also you should be using tinned copper wire so that your wirring does'nt corrode.

Frank

[rig_dude]

Bi metals and electricity don't mix. Always go back to the battery. Use qood quality cable and connections and you can't go wrong. Especially when you are running transducers as any kind of leaked voltage can disturb your sounders readings.

[therapy]

A big thanks to all respondents!! It sounds pretty unaminous then. I'm going to disconect that earth when I get home tonight and look at running a seperate earth back to the battery. There is already another earth block behind the dash so I might have to look at where that is earthed as well. Once again thanks to all you Ausfisher champions!! Great for a gumby like me to be able to ask questions and get an unbiased and informed answer!!
Cheers..............Terry..

[Mtx]

ask for half a bottle of bundy back

[PADDLES]

earthing of the hull (equipotential bonding) is normal but using the hull as an earth return to the negative terminal is bad. earth returns should be cabled.

[black runner]

Hull bonding and using the hull as an earth return circuit are two completely different beasts.

There are quite a few threads on this site and the web about ally hulls and earthing. The main thing to ensure is that all -ve cables are physically connected usually at a common point and this can in many cases be on a plate that is connected to the hull. This doesn't mean that the hull is being used as an earth return circuit. But it does ensure that the outboard (through a bonding strap or starter -ve cable) has the same electrical potential as the hull and that the hull is also connected to the annodes which offer sacrificial protection.

[Camo]

Hull bonding and using the hull as an earth return circuit are two completely different beasts.......ensure that the outboard (through a bonding strap or starter -ve cable) has the same electrical potential as the hull and that the hull is also connected to the annodes which offer sacrificial protection. BLACK RUNNER

Absolutley correct.

Camo