Hi All,
After extensive research here and elsewhere I am still struggling to understanding why STACER would recommend their resellers to ground their tinnies to the hull?
I have just purchased a Stacer 449 SC, and the dealer has given me a memorandum that STACER provided them with instructions to ground all outboards to the hull.
The outboard negative goes to my battery terminal, however a lead cable is mounted on a M6 stainless bolt that goes through the hull where all other accessories are wired negative.
Is this sound advise?
The above would make your hull live with 12V when battery isolation switch turned on, and effectively exposes your tinny to galvanic corrosion.
I understand that the outboard is grounded to the engine, thus to the hull. However, when tested produces 0V.
Should I ignore STACERS recommendation in this case and isolate my earth completely?
Cheers
Mark
Not exactly sure what you mean, the engine is usually grounded to the hull by bolts and all sort of other bits and pieces, making sure it is grounded will not hurt anything, and a battery isolation switch removes the positive from the circuit, kind of like removing the battery terminal.
some knowledge can be dangerous, full knowledge is enlightening.
The hull is "bonded" to battery earth. Its there to save your life. Removal is optional, lol. Thats from some reputable sources. Its NOT part of the electrical earth. All ccts earth should terminate at the battery. If you have multiple " bondings" or earths to the hull, corrosion will occur . I dont pretend to know all the answers yet, but i would think telwater knows their stuff. I am happy to be corrected.
No one is claiming to be an expert here, hence the question.
And if you dont pretend to know all the asnwers yet, why would you start your response with an insult?
Thanks for your words of wisdom!
GMy apology, i didnt mean it that way. I have correct it. Again, i apologise.
Thats just it, the outboard is electrically isolated from the hull it seems. When testing the continuity with the volt meter there is none.
I can see pvc spacers on each side of the transom and it looks like the bolts are also isolated.
All good matethanks for the response.
you want the hull to be bonded to earth at one spot ONLY as a general rule. It could be a quirk of the outboard's electrical system, thats a guess though. I think some background info is missing which would explain the memo. It wouldnt be just a random suggestion.
ok now , it was assumed that the motor is earthed. ie, 0V/neg connected to the chassis
Motors are not earthed.
Any power associated withthe outboard is isolated from the output 12v and motor chassis. Making sure its bonded to the hull s again for your safety. The motor body and hull play no part in the electrical system. 12v and negative, red and black etc etc etc.
thats where the zinc anodes on your outboard come into play. They are sacrificial to any stray currents. So in effect, if the outboard is isolated from the hull, and stray currents occur, the hull will be subjected to electrolysis.
starting to make sense to me .
I reckon they are just trying to cover their ass from the possibility of an electrical shock thru the hull hence to earth it and there covered by all means dont listen to there dribble about the hull needing to be earthed every earth should eventually lead back to the battery without touching the hull, the battery is the motor behind the electrolysis from my understanding the power running thru the earth electrifies the hull at very low voltage it may not even show up on a multimeter in return your hull becomes the sacrificial anode and u will see small spots that grow and grow
by leaving the earth connected to the hull and just switching it on when u use the boat just slows the process but it will still create electrolysis when u are using the boat and the switch is ON it will stop when u switch the switch to OFF because there will be no power to electrify your hull
i have mentioned this before my mates bought a $25,000+ boat that a rich range rover yuppy had no bloody clue he had a ON/OFF switch wired in and the earth line was bolted to the hull, some weeks later he must have noticed the hull pitting and leaking so he had someone spot weld the pitting and possibly leaks
my mates bought the boat after i inspected it and i mentioned why the guy was selling it for $14,000 because of the electrolysis and i mentioned it were highly likely due to that one earthed wire beside the ON/OFF switch we got it home unbolted the wire this was 3-4 years ago the boat is still going today no further electrolysis
Assuming your engine is indeed isolated from the hull (unusual for an outboard - I have never seen one that wasn't "negative earth" but given the plastic transom plates it is entirely plausible), there are a couple of reasons for the bonding wire to the hull. The first is to ensure that the hull is at the same potential as the motor. If it isn't it could set up galvanic corrosion and in a worst case fault scenario (if 12 volts positive were to short to the hull without the bonding) severe electrolytic corrosion.
I have also seen a case of an engine harness catching fire in a fault situation as one of the gauges was the only connection point between the hull and negative - the inboard engine being isolated but the gauge having an "old school" metal retaining bracket that was in contact with the negative terminal. In this situation the main accessory supply wire chafed through against the hull - sending the "isolated" hull to a 12 volt potential. The supply was fused at a rating that was sufficient to protect itself and it's negative but far in excess of the much smaller wire of the harness resulting in a fire and subsequent extensive wiring damage. A sufficiently heavy connection from the battery to the hull would have meant a blown fuse without the fire - inconvenient but a lot less exciting. Other common sources of hull "grounding" are metal cased stereos/radios and old school metal 12 volt sockets - they don't necessarily use the hull as a current path but do provide a connection that could present the same set of circumstances
As Scottar says above: both the hull and the motor are immersed in an electrolyte ( salt water ) and they need to be at the same potential so that current will not flow from one to the other through the salt water, thus creating galvanic corrosion.
What you don’t want is current flowing through the hull, all device negatives should go back to a single negative point rather than using the metal hull as a return. Or better yet get a plastic boat.
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I totally rewired my Bluefin when I bought it. Everything I added goes back to battery neg via double and sometimes triple earth wires not the hull. So I was a bit puzzled to see that the mutilmetre picked up.that the hull is ripping along at 12.5v approx when battery main switch is off (mutlimetre positive on battery and neg on hull though)....I can only assume that the outboard is earthing through the hull - t has its earth lead going to Batt 1 neg and positive lead going to the common post of the battery selector switch (both batteries are wired neg to neg).
So then I ran the mutilmetre over 2 of my mates alloy boats and same thing (and no wires on their boats are grounded to the hull that I could see - 2 x 40hp tohatsu electric start 2 strokes and 1 x yammy 20hp pull.start with aftermarket charging circuit) which means when the battery switch is on there is current flowing through the engine wiring and though the hull, back through engine to the battery. I dont see an easy way around this. My boat is 16 years old and has seen lots of salt water use and has not hull corrosion inside or out.
Cheers
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Boat: Seafarer Vagabond
Live: Great South East....love Moreton Bay fishing
Go easy buddy. You're the newbie jumping on here asking for help. I didn't see the original post, but there is nothing there now that should cause any offence.Originally Posted by wysiwyg
There is a whole lot of confusion here (I think) I'm somewhat baffled by some replies and methods, so, let's start right at the beginning, a 12V DC system (a battery) is about as simple as you can get, but when you start adding "stuff" this simplicity can get very complicated, especially devices that have a "memory" to keep preset information stored for future instant use. All equipment should have a seperate positive, and a seperate negative, connected (kind of) directly to the battery, unlike your car, that uses the metal body for the negative, boats should not do this! Why you ask, in simple terms (very simple) your boat is used in an electrolyte (sea water) that conducts electricity, your car does not. In most cases (metal boats) the motor is bolted to the boat, along with steering and so on, the negative is connected to the motor, and everything is happy, why or how in this case the motor is isolated is anyone's guess, I am going to a Telwater dealer later to see what they are up to, and will report back.
I think it's an American thing Noel, they wanted to comply with the US rules but it can cause electrolysis if a fault occurs in the wrong place.
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