Earth leakage on boats
Submitted by grahaml on Mon, 2016-05-09 15:46
gents
I've been told that the earth/negative on a boat should never be grounded and yet on my quintrex the negative battery lead is bolted to a lug on the transom near the battery box.is this correct or should I remove it from the connection to the hull so it's not grounded
the negatives for lights ect all come back to the lug on the transom
meglodon
Posts: 5981
Date Joined: 17/06/10
Negative battery pole should be used
All earthing/negative/ground returns should come back to the negative pole on the battery. If the ground/negative/earth uses the boat, then the boat becomes part of the circuit and will cause electrolysis to occur in the boat and thus corrosion will occur.
Comrad
Posts: 109
Date Joined: 17/07/14
This isn't how electrolysis
This isn't how electrolysis works. Electrolysis is a non-spontaneous redox reaction that occurs from an anode to a cathode via an introduced electical charge. If the hull were grounded, and in electrical contact to the conductive water, all that means is that the ocean acts as a giant negative node. Unless the positive terminal was shorted in the ocean/to the hull, this isn't relevant.
I feel that its poor practice to connect a negative terminal to the hull since the surrounding area is conductive as opposed to a car where the typical surrounding environment isn't conductive, but, its not a process of electrolysis. Even if it were the case of electrolysis, you'd be stripping ions from the positive terminal of the battery onto the hull/ocean node, you're not stripping anything from you hull, as some people believe.
Electrics are one of those things where if you're trying to get concrete information, a public forum probably isn't the best place to ask.
Endurance Marine
Posts: 15
Date Joined: 29/03/16
Depending on
Depending on configuration/boat/device setup, would recommend installing a insulated stud or earth bar and terminate your negatives to this and one suitably sized cable back to the negative terminal on the battery. This way it will be neater and easier to work with down the track and be less prone for problems. Never terminate negatives to Ali hulls as mentioned.
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grahaml
Posts: 54
Date Joined: 21/09/11
Thanks for the info I'll be
Thanks for the info I'll be tracking down a stud
cheers
epic restos and...
Posts: 226
Date Joined: 22/06/15
disconnect straight away use
disconnect straight away use a non coducting fixing point or buzz bar not good at all even if you can isolate your battery
CCC
Posts: 539
Date Joined: 29/03/10
There is a difference
There is a difference between having the battery earthed and using that earth to power electronics.
Your engine is earthed to the hull through the transom bolts. You will see many boats with an earth strap going to the hull from the negative terminal on the battery. This must not be confused with using the hull as an earth to power up gear.
sea-kem
Posts: 14983
Date Joined: 30/11/09
Why the hell do Quintrex do
Why the hell do Quintrex do this then? Earth to the body? I've spken with a couple of members here and they have explained the same as above. Gets you scratching your head.
Love the West!
JohnSorrell
Posts: 137
Date Joined: 28/07/09
All outboards are grounded to
All outboards are grounded to the hull via the mounts! I think it would be impossible to isolate completely. Don't forget that outboards also have a sacrificial anode, which will corrode before the hull.
If you use the hull as a grounding point for your electronics (i.e. only 1 wire connecting +ve to the batt and -ve to the hull at closest point.... then you will have issues.
All electronics should have 2 wires direct to the battery or a isolated common point which connects direct to the battery.
In any case.. It would seem that your common point is at the battery...
Do you have 2 large wires connected from the engine block / starter motor / solenoid direct to the battery?
If so, you will not have any issues with hull corrosion, even if the outboard is grounded to the hull.
Gone Fishing...
Starbug
Posts: 563
Date Joined: 27/08/09
So if you ground your
So if you ground your battery to the hull, and your outboard is grounded by being bolted to your transom you will have current flowing in your hull.
The battery to hull to outboard conection forms a parallel path with the negative lead to your outboard. While your engine is running you will have current flowing in that hull path! Not good!
JohnSorrell
Posts: 137
Date Joined: 28/07/09
sorry to bring up an old
sorry to bring up an old thread, but... the resistance of the hull is higher than the resistance of the cable of which the current flows from the battery to your electroncis / starter moter ect.... Current will always follow the path of least resistance... So stick it up ya bum. There should be no current flowing through the hull if the cables are sufficient size to cater for the electrical load.
Gone Fishing...
ranmar850
Posts: 2702
Date Joined: 12/08/12
It is not a car, its a boat.
Vehicles commonly use the frame as earth return to save running a negative to every point. half your problems with dodgy auto electrics will be down to bad earth connections. The hull of an ali boat will always be earthed due to the fact that the earthed frame of the outboard is in contact with it. But that isn't the same as using the hull as a negative return path. IF you are using a stud connected direct to an ali hull with everything earthed to it, as well as negative wiring, the hull will still conduct as it is a parallel path. Yes,the current will be proportionally higher on the path of least resistance, but it will still take the other path AS WELL if there is a circuit completed.. The only place your electrical system should have a negative in contact with the hull should be at the motor frame, end of story.
JohnSorrell
Posts: 137
Date Joined: 28/07/09
I'm not saying that you
I'm not saying that you should use the hull as a grounding point.. that is silly... I'm saying that there will always be a common connection between the hull and the -ve battery terminal, and if you do not use sufficient gauge cable to connect both +ve and -ve from all electronics directly to the battery, you will find stray currents will flow thru the hull...
Also if youve ever seen a standard fuel level sender mounted to an ali tank, they do not usually have an isolated ground because the -ve terminal is part of the metal frame which screws to the metal tank... many people forget to run a wire to the -ve terminal of the sender direct to the battery and wonder why they go through so many of them.
Gone Fishing...
marrisy
Posts: 202
Date Joined: 08/09/11
Google Galvic corrosion,
Google Galvic corrosion, capacitors, it's not a good idea to use the hull as a conductor. The science behind the effect is too great to discuss here,..
ranmar850
Posts: 2702
Date Joined: 12/08/12
Perhaps if you had not dragged up a 7 year old thread
And told us to stick it up our collecttive bums, you may have more credibility.