New Boat Grounding Question

[wysiwyg]

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

[Noelm]

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.

[Andy56]

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.

[wysiwyg]

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!

[Andy56]

GMy apology, i didnt mean it that way. I have correct it. Again, i apologise.

[wysiwyg]

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.

[wysiwyg]

All good mate :) thanks for the response.

[Andy56]

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 .

[gazza2006au]

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

[scottar]

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

[swof63]

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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[ozscott]

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

Sent from my SM-G960F using Tapatalk

[Jeremy]

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!

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.

[Noelm]

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.

[Fed]

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.

[Andy56]

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.

The reason people get so hung up is because the terms are not easily understood and are all interchanged.
How do you define earth? How do you define battery return, earth or neg?
Thats why i used the term " bonded", so as not to confuse the issues.
.
all elevtrical circuits are run to the battery, both positive and neg/earth. NOTHING connected to the hull. That includes the motor electrics.
the hull is then bonded to the neg of the battery in one spot only. So there is no resistance between hull and motor chassis, the motor chassis should be in full contact with the hull. This way you have personal safety taken care of and any electrolysis occurs through the motor zinc plates. Thats why they are there.
from an elctrical/safety point of view this makes perfect sense.

For the more technically inclined, here it is again.
There are two electrical circuits in play one the 12v power system. Battery , alternator and electronics. Totally self enclosed with no contact to the hull. Old radios with a metal chassis should be completely isolated from the hull.

the second circuit components are saltwater , aluminium and zinc. Its about 1.1v.
There will be wear on the zinc so that the aluminium is preserved. Sacrificial is the term. This is normal behaviour. So the motor must be tied to the hull to work as designed.
these two systems are bonded for your protection. A faulty system earth means you are the potential earth!
They DO NOT interact. So guys are thinking they interact and come up with amazing hypothecies. If there is interaction, you got something wired incorrectly.

Of coarse, life isn't perfect and with all things electrical/electronics there are times when the tolerances are so out of wack funny things happen. These times are then thrown out there as "normal". Bad news travels fast, good news never makes it, lol.

stick to best practices which work 99% of the time. Sure the 1% happens, but it shouldnt be your main concern unless it happens. By then you need to consulte an expert, an earth "whisperer".

from where i stand, its easy to see why you have different responses from different folks. Get ther terminology wrong and you get tongue tied, misunderstand cause and effect and you get it all wrong. Hence why i started with an insult, which really wasnt called for. But then again...............
" i isolated the motor and i get no more corrosion". Lol, thats funny if somewhat misguided.

[Andy56]

What i would be looking at is wear indicators n the motor zinc anodes.
If there is no wear, i would be worried that the hull is dissapearing or that i am in danger of a potential electric shock. Rapid wear and i would be lookin for a bad connection somewhere. As these thngs are designed, there is a goldielocks rate of deterioration.
sure people have the motor totally isolated and never have a problem, but thats taking a risk in my opinion. Thats why stacer put out the memo.

[scottar]

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

Sent from my SM-G960F using Tapatalk

What you are seeing is what I would term "normal" for an outboard powered alloy boat. You are seeing the hull at the same potential as the outboard courtesy of the connection via the bolts through the transom. This doesn't mean any current will be flowing through the hull providing there are no accessories using the hull as a negative and there is no stray positive voltage source anywhere - unsealed wire joiners in the bilge and battery switches that just touch the paint are the two I have encountered most frequently.

[ozscott]

Thanks m8. Every join at hull level is well insulated and away from floor etc. Battery switch is backed into 22mm form ply and it is sikaflexed to the hull. I didn't muck around when I rewired the boat. Everything save the Minn Kota and motor runs from a PVC control box with fuses/breakers for each circuit from bus bars inside the box and the bus bar positive served up via a circuit breaker between the battery switch common positive and the bar. No wires are able to rub. Very pleased with it all. My 4th full boat rewire and it's my best. My last too probably. Everything is tin coated copper wire too.

Cheers

Sent from my SM-G960F using Tapatalk

[jclay1773]

Poor bloke just asked a question and got some smart arse comments. Just because a big brand does it doesn't mean that its right.

I'm no expert but isn't it as simple as motor being earthed to hull and all other 12v items being earthed to battery. Battery does not get earthed to hull.

[ozscott]

Hi Jclay. Your message box is full but in reply I'm happy to help mate. I will shoot you some photos. Have to give me to mid week or so. I have some somewhere of inside of control box and I will take some of battery switch. How are you for 12v wiring knowledge? About 20 years ago I bought the 12 Volt Doctors Guide to Boat Wiring...best thing I ever did in terms of boat fitouts. You can still get it. Cheers

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[Andy56]

Poor bloke just asked a question and got some smart arse comments. Just because a big brand does it doesn't mean that its right.

I'm no expert but isn't it as simple as motor being earthed to hull and all other 12v items being earthed to battery. Battery does not get earthed to hull.

as i said, sometimes not knowing the full story means you draw the wrong conclusions. The battery is not EARTHED to the hull. Its BONDED. Its done for your protection. ITS NOT an ELECTRICAL EARTH or earth path.

The motor chassis is bolted to the Hull. This way any electrolysis results in the zinc anodes on the motor corroding away and NOT THE HULL.
Its pretty straight forward once you understand the concepts. Being cynical with the big boys is misplaced on this topic.

I wonder how many people complaining about pitting on their tinnies have the motor chassis "floating" off the hull? You can have all sorts of crazy off beat ideas, but if you dont understand what your doing , you are playing in the dark. In Thailand its called monkey see monkey do, lol.

[jclay1773]

So wouldn’t the original poster have an issue as the motor is connected to battery which is then connected to hull where the rest of his 12v circuit is.

Edit.... how is a battery bonded to a hull?


Ps. Not sure who the big boys are.

[jclay1773]

Hi Jclay. Your message box is full but in reply I'm happy to help mate. I will shoot you some photos. Have to give me to mid week or so. I have some somewhere of inside of control box and I will take some of battery switch. How are you for 12v wiring knowledge? About 20 years ago I bought the 12 Volt Doctors Guide to Boat Wiring...best thing I ever did in terms of boat fitouts. You can still get it. Cheers

Sent from my SM-G960F using Tapatalk


thanks mate appreciate that. Will look into the book.

[Andy56]

So wouldn’t the original poster have an issue as the motor is connected to battery which is then connected to hull where the rest of his 12v circuit is.

Edit.... how is a battery bonded to a hull?


Ps. Not sure who the big boys are.

Yes i would say there is an issue hence why stacer put out the memo. Nothing to say that the battery negative has to be any distance from the hull. So long as there is ONLY one good connection thus so.

The battery earth is bonded to the hull via a strap . Or as in this case a one point bolt. Its only an issue if you dont understand why its done. Same as neutral is hard wired to the earth stake in your home. You do know its for your protection?

Its an issue when the motor is totally isolated and you have multiple earthings to the hull. Multiple earthings implys that the hull becomes part of the electrical ccrt. This is not what we want. If done correctly, the hull is not part of the power electric circuit.
Making the hull part of the electric circuit will induce stray currents and galvanic corrosion.
BONDING does NOT make the hull part of the electric circuit. Irrespective of what your meter says, you have to understand what it is you are measuring.
If you put a meter between 12v pos and neg you will read 12v, same as 12v positive to hull. BUT IT IS MISLEADING to think they are the same. If you think current, !.54A will flow out of the positive terminal and 1.54A will flow into the negative terminal. If you measure the current from 12v positive to the hull, you will get a very , very small reading. The amount of leakage is so small as to be negligible. The electrons dont " return" via the hull. Sure over a long period of time it may add up, but the zinc anodes on the motor will take care of that. If you do make the hull part of the electric circuit, electrons will return via the hull and lots will disappear into the water causing corrosion at that point.

No doubt its still clear as mud to some, but i hope others get something out of it. I certainly had to think a bit about it. I did lots or research and I am an electronics guy. (certif of technology- communications, broadcasting officer) AND i just bought a tinnie too!

[ozscott]

Nice explanation Andy. The lack of amps ie what made me content with seeing 12v.at the hull. I assumed because the motor was not live the 12v was not part of a circuit as such. Cheers

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[Andy56]

its all to do with understanding the concepts. Power circuit, galvanic circuit and personal safety.

WYSWYG, i hope its clear why stacer put out the memo.

Gazza, i hope you now understand why cutting that earth fixed the problem, the right thing for all the worst reasons, hahahaha. sometimes you just gotta get lucky.

[swof63]

Nice explanation Andy. The lack of amps ie what made me content with seeing 12v.at the hull. I assumed because the motor was not live the 12v was not part of a circuit as such. Cheers

Sent from my SM-G960F using Tapatalk

Just to clarify, you weren’t seeing 12v at the hull, you were seeing 12v at the battery. Voltage is a potential difference between two points, it’s the ”pressure” wanting to push the electrons rather than the “flow” which is current. Putting one lead from the meter on the battery +ve and the other on the hull ( which due to the “bonding” is at the same potential as the battery -ve), you will essentially be reading the voltage across the battery terminals. You were reading before the +ve went through the battery switch which is why you got 12v with the switch off. This is normal.


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[ozscott]

Thanks m8. Yep I understand. The hull has become part of the battery. No difference to running a piece of steel off the battery neg and connecting neg of multimeter to that and post of MM to battery pos...you are just extending the battery and showing 12v as the potential energy but with no amps or virtually none flowing because there is no draw...no filament, LED, radio etc on that circuit to excite electron flow and use power.

Cheers

Sent from my SM-G960F using Tapatalk

[Andy56]

Just to clarify, you weren’t seeing 12v at the hull, you were seeing 12v at the battery. Voltage is a potential difference between two points, it’s the ”pressure” wanting to push the electrons rather than the “flow” which is current. Putting one lead from the meter on the battery +ve and the other on the hull ( which due to the “bonding” is at the same potential as the battery -ve), you will essentially be reading the voltage across the battery terminals. You were reading before the +ve went through the battery switch which is why you got 12v with the switch off. This is normal.


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I guessed thats what he meant.

[Andy56]

Its like a circuit that has the switch in the off position. , so no current draw.

[wysiwyg]

Thank you for all your responses and I appreciate your time.
I think its now confirmed for me that I should isolate the negative terminals from the hull contrary to what the manufacturer recommends.
As stated above, when main switch is turned ON, the hull is live, thus while in the water electrolysis is occurring.
I have also consulted a few local boat maintenance professionals including electricians, and they have also confirmed that the manufacturers advise goes against what they have been taught for years.

Thanks again

[wysiwyg]

BTW, here is a copy of the Service Bulletin 2014 from telwater

117483

117484

[Andy56]

i cant seem to open the attachments.
So when you switch on the power your measuring 12v from the positive to the hull. Do you actually know what your measuring? The hull IS NOT PART OF THE ELECTRICAL CIRCUIT with the "Bonding". No current flows from the hull to the battery. If you put the meter between the hull and battery earth you will see 0V, Measure the resistance and it will also be zero. so therefore its not a circuit. V volts =I current X R resistance. So basic maths will tell you zero divided by zero = zero current!! . ( the zeros are all approx. ) Pretty basic electrical and maths stuff here.

despite my best efforts, it appears you still dont understand whats actually going on.

If you disconnect the bonding of the battery neg to the hull, you will still get electrolysis. Aluminium to saltwater is about 1.1V. With no sacrificial zinc anode, since the motor is isolated, your hull will suffer to some degree. BONDING OR NO BONDING you will get electrolysis.

As I said, you have to come to terms with the concepts . There are good reasons why its done a certain way. I have tried to explain in simple terms.

Have all the experts you consulted explained whats actually going on? Be interesting to actually hear what they say, cause I for one think they talk crap. Monkey see and monkey do is not a valid explanation. I am open to reasoned explanations that follow basic electrical principles, not opinions. Opinions dont change the laws of physics.

But hey, its not my place tell you what to do. You need to weigh up who you trust. I have an electronics background so I know a thing or two about earthing. Others have different experiences. They have worked with boats before, fine, i can deal with that. But i certainly learned a few things doing the research and i think what i have explained is very sound.

[Noelm]

I must admit I am bamboozled by all the to and fro, I fully understand what goes on and why, but for some reason, it's getting twisted around, I think Telwater are correct by the way! measuring from the battery positive to any ground/earth/bond/negative will always show 12V.

[gazza2006au]

BTW, here is a copy of the Service Bulletin 2014 from telwater

117483

117484

My mates boat i mentioned was wired exactly like that picture and the hull was covered in electrolysis i unbolted the two black earth wires from the hull and just bolted them back together than taped them and it stopped all the aluminum cancer in its tracks

The reason behind telwater and stacer saying to earth the hull is because if u launch the boat on a calm beach u act as a electricity magnet while standing in the water holding the boat before u jump in, if there is a stray wire u will be electrocuted,with the hull earthed u should be fine so these companies are just covering there asses in case a lawsuit is filed, could be quieta substantial amount of cash payout if u have a pace maker and can u imagine how many older boaters out there have them?

i worked this out personally one time when i blew up a jetski i was standing knee deep on the beach trying to do up my battery terminals with a metal screw driver and i felt my legs burning than i felt my finger tips tingling and worked out i was conducting electricity i cannot remember if it were from the + or - terminal but i do remember it

[wysiwyg]

Andy,

I appreciate your patience, and thank you again for your input.
Sorry you had issue opening the attachments, but i think I have fixed the problem.
I have also attached a below wiring schematic that I have found, the point here is every wiring diagram I look at the on the web, common ground is always isolated from the hull and on a bus bar.
Not anywhere have I seen a diagram where the ground or -ve is simply connected to the aluminium hull.
All negative cables, from any accessory are always brought back to the common negative bus bar, unlike a car where you simply attach to the chassis.
In my boat currently, when switch is turned ON, and I use the meter to measure voltage, I have one node attached to positive of the battery and the other to any part of the hull and I read 12V.
If I disconnect the grounding wires from the hull bolt as telwater recommends and I perform the same test I do not get a reading at all. And yet, the engine manages to start and all the accessories still work and I do not get a 12V reading off the hull.
Sorry If I am not understanding this correctly, but I am just conveying what I am observing.

117485

[swof63]

Wysiwyg, your hull ain’t live. As said above, if you measure between the battery NEGATIVE and the hull and get 12v, you have a live hull. If you measure 0v you don’t, you have a hull at earth potential.
Making a decision to cut the earth bonding and go against established theory is obviously your right, but it’s clear this is not a discipline you are educated in so making such a decision is a big risk for you.
I don’t think it’s a safety issue - 12v dc is pretty safe, as much as a corrosion issue.
I initially thought a bad earth return ( faulty) from motor to battery could result in elevated potentials from the ignition cct on the engine block but if most modern motors have no earth the efi ecu won’t work anyways. Starter motor won’t work proper either.


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[scottar]

Andy,

I appreciate your patience, and thank you again for your input.
Sorry you had issue opening the attachments, but i think I have fixed the problem.
I have also attached a below wiring schematic that I have found, the point here is every wiring diagram I look at the on the web, common ground is always isolated from the hull and on a bus bar.
Not anywhere have I seen a diagram where the ground or -ve is simply connected to the aluminium hull.
All negative cables, from any accessory are always brought back to the common negative bus bar, unlike a car where you simply attach to the chassis.
In my boat currently, when switch is turned ON, and I use the meter to measure voltage, I have one node attached to positive of the battery and the other to any part of the hull and I read 12V.
If I disconnect the grounding wires from the hull bolt as telwater recommends and I perform the same test I do not get a reading at all. And yet, the engine manages to start and all the accessories still work and I do not get a 12V reading off the hull.
Sorry If I am not understanding this correctly, but I am just conveying what I am observing.

117485

The reason you aren't finding any reference to it is that it is most unusual to find an outboard powered alloy hull where the engine is isolated from the hull. The outboard is "grounded" to the negative - ie the negative is attached to the engine block - totally normal. Normally the hull is bolted to the outboard in a fashion that then means the hull is "grounded" to negative as well via the outboard - once again, totally normal. As Telwater has rightly pointed out in their literature, that electrical connection via the bolts can be less than perfect due to paint, silicone etc which is not a great situation if it is too poor. If you are to take off the negative bonding wire, you run a significant risk of quickly dissolving your outboard if by chance a positive wire chafes through and makes contact with the hull. You will basically be setting up a battery by removing it anyway - the old school experiment with dissimilar metals in a lemon creating a voltage - but this will be slower.

[wysiwyg]

The reason you aren't finding any reference to it is that it is most unusual to find an outboard powered alloy hull where the engine is isolated from the hull. The outboard is "grounded" to the negative - ie the negative is attached to the engine block - totally normal. Normally the hull is bolted to the outboard in a fashion that then means the hull is "grounded" to negative as well via the outboard - once again, totally normal. As Telwater has rightly pointed out in their literature, that electrical connection via the bolts can be less than perfect due to paint, silicone etc which is not a great situation if it is too poor. If you are to take off the negative bonding wire, you run a significant risk of quickly dissolving your outboard if by chance a positive wire chafes through and makes contact with the hull. You will basically be setting up a battery by removing it anyway - the old school experiment with dissimilar metals in a lemon creating a voltage - but this will be slower.

I am leaning towards the fact that the reason why my outboard is fully isolated is due to a total fluke occurrence. As its a new boat I am leaning towards the possibility that the silicone or whatever was used has inadvertently isolated the hull.
Perhaps I should remove the bolts one at a time and re-insert them and see if I get continuity between the hull and the outboard. Maybe over time the outboard will align itself in its holes and eventually start touching the aluminium hull.

So now lets assume that the outboard is grounded to the hull.
Based on the wiring diagram 117488 attached, it is still recommended that all negative and ground wires are wired to a common bus bar and not the hull. Source of attachment image is Ausfish.com.au.

[gazza2006au]

Your right Scottar i rebuilt a mercury 25hp big foot 4 stroke one of the early models which had heaps of electrical wiring i thought i had it all connected because i just followed the colour to colour, one night we were sitting out on thewater justafter i had rebuilt the engine and we heard a sizzling and popping sound than it turned into a loud cracking sound i thought shit this can't be good quickly pulled her out and the bottom of the engine transom mounts were being eating away in minutes from electrolysis i some how hooked up the wrong wires, i looked thru the workshop manual and corrected y wiring i think from memory i had 2-3 wires incorrect once fixed it was all fine

[Andy56]

What telwater are not telling you but is implied by the wiring is that the anodes on your motor are sacrificial so as to protect the hull. If you pull the bonding wire, the anodes protect the motor but not the hull. Your hull then forms a circuit with the saltwater, 1.1v. THIS DOES pull current through the hull.

The normal galvanic circuit consists of saltwater + zinc anode from motor +alluminium hull. As the electrons exit via the zinc they take a few atoms with them.
Now if you eliminate the zinc, the electrons exit via alluminium and take a few atoms with them. Surely you can understand this concept !!


All i can say is that there are reasons why and they are not just by chance. Covering their backs gazza? Quite possibly. I used to play with 12v all the time on a bench and it was very safe. Lots of resistance so little current flow. On a wet boat, it could be lethal. Those batteries can quite easily deliver a few amps. only need 30mA to kill you. I'd say they dont want ANY bad publicity, lol. Besides to do it right cost no more than doing it wrong. I guess there are electrical standards too that would define how things are done. I guess because i dont know for sure but australian standards cover your jocks in most other electrical matters. You cant produce a product that could be lethal and survive in this day and age.
Warranties. If you dont do it their way, your warranty is void. This is surely the biggest incentive.

[ozscott]

Look...just a trigger word for me...if you are 'electrocuted' you dont stay around to talk about sizzling/tingling sensations...you are dead (ie tbe cuted bit). Electric shock is what you typically feel in a 12v system unless you have a dodgy heart etc in which case the shock may turn into electrocution.

Cheers

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[Andy56]

If you read carefully. They say its about boats delivered without an outboard.
Based on the attachment 117488 ( which i cant open), they are RIGHT. you are confusing the terminology. Thats why I call it BONDING and not earthing. To distinguish what it is your actually doing.

[swof63]

Again, it’s primarily a corrosion issue, and possibly also ensuring that any wiring faults blow fuses rather than smoulder and burn.
An electrical shock that will seriously damage or kill you needs to be above 30mA ( and in reality normally above 75mA) and below 200mA directly across the heart. About the only way to do that with 12v is to have two needles directly inserted into the myocardium and introduce the current directly across the tissue. In normal practice it’s going to be external hand-foot or hand-hand exposure. Even wet skin has a minimum resistance of about 1000ohms or so ( dry up to 100,000ohms) and then the typical hand-foot body resistance of about 500ohms ( hand-hand similar ) would give you about 5mA assuming both hand and foot wet. I started out as a biomedical technician - isolation, leakage, macro shock, micro shock were daily grist. In external situations anything below 32v dc was low voltage.
Reality check people: how many times have you touched an installed car battery positive terminal with either your hand or a tool, whilst another part of your body was touching metal or ground? I bet you didn’t die.


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[Andy56]

Again, it’s primarily a corrosion issue, and possibly also ensuring that any wiring faults blow fuses rather than smoulder and burn.
An electrical shock that will seriously damage or kill you needs to be above 30mA ( and in reality normally above 75mA) and below 200mA directly across the heart. About the only way to do that with 12v is to have two needles directly inserted into the myocardium and introduce the current directly across the tissue. In normal practice it’s going to be external hand-foot or hand-hand exposure. Even wet skin has a minimum resistance of about 1000ohms or so ( dry up to 100,000ohms) and then the typical hand-foot body resistance of about 500ohms ( hand-hand similar ) would give you about 5mA assuming both hand and foot wet. I started out as a biomedical technician - isolation, leakage, macro shock, micro shock were daily grist. In external situations anything below 32v dc was low voltage.
Reality check people: how many times have you touched an installed car battery positive terminal with either your hand or a tool, whilst another part of your body was touching metal or ground? I bet you didn’t die.


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granted you may be right about the amount of current to kill butyou have to allow a certain safety margin. My experience with electroncs is that if it can happen, it will. You have to allow for the odd bod who doesnt need much to kark it. Earth leakage devices operate from 10mA to 40mA. So you have to assume a certain margin. Its no good later saying " that's never happened before".
so after saying that, i went back to the research and can say that its higher than 75mA even, but it all depends on circumstance. AC or DC current, skin condition, place of contact ie hands or chest etc etc . My take is keep a safe margin when i calculated these things.
i do agree with your opening line.

[seastrength]

I must admit I am bamboozled by all the to and fro, I fully understand what goes on and why, but for some reason, it's getting twisted around, I think Telwater are correct by the way! measuring from the battery positive to any ground/earth/bond/negative will always show 12V.

I have been following this thread with much interest, but remain somewhat confused by the various expert opinions. I have recently taken delivery of a new 6.2M platey and decided to attach a zinc electrode block to the hull on the left spare transducer bracket. My thinking, after owning a second hand tinny for 5 years with multiple corrosion spots over the hull, was that a sacrificial anode directly attached to the alloy might prevent a similar problem in the new hull. Being an electrically challenged individual, I was hoping this would prevent any galvanic corrosion of the hull, hypothetically being the sacrificial anode would corrode in favour of the aluminium. I am not sure whether the electrical circuits are grounded or bonded to the hull and motor, as all electrical were done by the local boat builder and as mentioned, I have no idea of circuits other than how to turn the system on an off via the isolation switch. There is no evidence of corrosion or pitting on the hull to date after 130 hours in salt water and I do a thorough wash down after each trip. Any help and explanation is greatly appreciated. I just want to be sure I have done the right thing (or more importantly, not the wrong thing in tis case). Cheers SS

[Andy56]

I have been following this thread with much interest, but remain somewhat confused by the various expert opinions. I have recently taken delivery of a new 6.2M platey and decided to attach a zinc electrode block to the hull on the left spare transducer bracket. My thinking, after owning a second hand tinny for 5 years with multiple corrosion spots over the hull, was that a sacrificial anode directly attached to the alloy might prevent a similar problem in the new hull. Being an electrically challenged individual, I was hoping this would prevent any galvanic corrosion of the hull, hypothetically being the sacrificial anode would corrode in favour of the aluminium. I am not sure whether the electrical circuits are grounded or bonded to the hull and motor, as all electrical were done by the local boat builder and as mentioned, I have no idea of circuits other than how to turn the system on an off via the isolation switch. There is no evidence of corrosion or pitting on the hull to date after 130 hours in salt water and I do a thorough wash down after each trip. Any help and explanation is greatly appreciated. I just want to be sure I have done the right thing (or more importantly, not the wrong thing in tis case). Cheers SS

Thats what they do on large vessels, a large zinc anode attached to the hull.

[scottar]

The zinc won't hurt but once the boat is on the trailer it will do precisely diddley squat. On larger boats the zinc is there as a sacrificial anode to take care of galvanic corrosion due to disimillar metals used in consruction. Some makers also go to great lengths to ensure the hull is isolated with many vessels having DC "earthing" fault indication systems. Ship's chief engineers in particular can get quite animated when you inadvertantly install a "negative earthed" accessory. A lot of this has more to do with electrolysis faults induced if differently wired vessels are plugged into the same shore power network in close proximity to each other - effectively making one boat dissolve.

On my last tinnie I ran a dual pole isolator so that everything was totally disconnected when the boat was in the shed. It still got pin holes starting up in various random places. Keeping salt out of areas that you can't wash properly and making sure you wash everywhere you can with something to break the salt down (fresh water isn't good enough on it's own) is key to keeping an alloy boat corrosion free.

[Andy56]

The zinc won't hurt but once the boat is on the trailer it will do precisely diddley squat. On larger boats the zinc is there as a sacrificial anode to take care of galvanic corrosion due to disimillar metals used in consruction. Some makers also go to great lengths to ensure the hull is isolated with many vessels having DC "earthing" fault indication systems. Ship's chief engineers in particular can get quite animated when you inadvertantly install a "negative earthed" accessory. A lot of this has more to do with electrolysis faults induced if differently wired vessels are plugged into the same shore power network in close proximity to each other - effectively making one boat dissolve.

On my last tinnie I ran a dual pole isolator so that everything was totally disconnected when the boat was in the shed. It still got pin holes starting up in various random places. Keeping salt out of areas that you can't wash properly and making sure you wash everywhere you can with something to break the salt down (fresh water isn't good enough on it's own) is key to keeping an alloy boat corrosion free.

Yes its all about understanding the concepts. Its then easy to work out why.