My aluminium hull has 12.4 volts running through it?

[Crocodile]

Hello to all the electrical gurus,
I have been tidying up the wiring behind the dash and I have discovered that I have 12.4volts between the positive bus and the aluminium hull.
Clearly an un-desirable situation.
It only reads when the large cables to the outboard are connected to the battery.
I have also discovered that a continuity test between the earth on the starter motor and the hull indicates a connection, the meter beeps.
Is it normal for a Yamaha outboard to be earthed to the aluminium hull?
Is this a problem?
Will it cause accelerated electrolytic corrosion?
Am I being paranoid?
Thanks in advance.

[gazza2006au]

i hate electronics but ive been told in a similar situation all earths need to run back to the battery u shouldnt earth any cables to the aluminum hull

[Firsttimefisherman]

Agree with gazza. Ensure everything runs back to the battery and not the hull. I also disconnect the battery while the boat is not in use.

[Chang Jiang]

I have seen on three occasions in last 6 months in NQ that mechanics have earthed the motor to the hull instead of running the wire to the engine, ( lazy and saving wire) this is contrary to instalation guides and down right incompitent. You should have a postive and negative bus bar both fully insulated from hull,
your out board normally has a small earth strap that connects to a zinc annode and this allows for stray from motor.

To keep wiring as simple as possible run all your instruments and lights through your bus bar , it will make fault finding very simple

cheers Terry

[TheRealAndy]

you engine will be earthed, so you should read 12V (give or take) between your hull and positive. Perfectly normal.

However, to avoid current loops, all other wiring should technically be grounded only to the battery, although this argument is questionable.

[Spaniard_King]

you engine will be earthed, so you should read 12V (give or take) between your hull and positive. Perfectly normal.

However, to avoid current loops, all other wiring should technically be grounded only to the battery, although this argument is questionable.

Andy is exactly right!!!!!

The engine earth is the whole engine, it has to be bolted to the boat hence if you will have a 12 v circuit if any positive side of the electrical circuit touches the hull.

As stated before ensure all negatives are of sound connection and run back to the battery.

for added protection you can add an additional isolator between the engine and battery on the negative side, this will assist in electrolosus protection when the engine is not being used.

[MyWay]

on my last bar crusher I install plastic washers on engine bolts and plastic sleeves with plenty sikaflax and on trim tabs etc
and all steering components and got down to 0v.

it was just me I did not like idea of having 12v there but it is normal because engine is bolted to hull

[Noelm]

you engine will be earthed, so you should read 12V (give or take) between your hull and positive. Perfectly normal.

However, to avoid current loops, all other wiring should technically be grounded only to the battery, although this argument is questionable.

I don't know how many times I have "debated" this point, of course the motor is earthed to the hull, I don't know of ANY boat that someone has insulated the motor from the hull!

[Jarrah Jack]

I found the same thing with my old Quintrex and put an isolator on the neg side as Garry suggested. There was no evidence of any harm done by the neg current over thirty years or so.

[Fed]

FWIW Mercury say the connection between the motor & the hull offers corrosion protection to the hull via the outboard anodes.

[BigE]

Never thought of the outboard anodes protecting the ali hull..... if they protect the motor is there any reason to believe they would not protect the hull???

BigE

[Chang Jiang]

I don't know how many times I have "debated" this point, of course the motor is earthed to the hull, I don't know of ANY boat that someone has insulated the motor from the hull!

I am sure i am not the only builder who builds to Class and in most instances best practice, www.armacraft.com (http://www.armacraft.com) ok my smallest boats are 6m in every aluminium boat we build there is no ground on the hull, all out boards are fully insulated from transom and if inboard we go dual pole and insulate engine from mounts . when i refered to mechanics earthing to hull , they are running a 1m negative cable directly to the hull and not the battery if this is best practice I believe we have problems with electronics in our boats.
In my opinion

[TheRealAndy]

I am sure i am not the only builder who builds to Class and in most instances best practice, www.armacraft.com (http://www.armacraft.com) ok my smallest boats are 6m in every aluminium boat we build there is no ground on the hull, all out boards are fully insulated from transom and if inboard we go dual pole and insulate engine from mounts . when i refered to mechanics earthing to hull , they are running a 1m negative cable directly to the hull and not the battery if this is best practice I believe we have problems with electronics in our boats.
In my opinion

In my opinion, isolating the engine from the boat is a bad thing to do unless you fit separate sacrificial anodes directly to the hull.