Electrical leak on aluminum boat

big.griff

big.griff

Active Member
Looking for some help or insight on this topic. Not sure why I started checking but I did. I am seeing a possible electrical leak on my fairly new aluminum boat. With battery switch on but nothing powered up, I don't get much of a reading with my multimeter. However, as I start turning things on, the readings increase. With all electronics, lights, bilge pumps turned on, I am getting around 50mV and 10-15mA. No one particular device seems to give a dramatic increase. All of this has been out of the water on a trailer. Boat is a year old and all negative wiring runs either direct to the battery or to a negative bus at fuse block. Is this too much stray current or am I being paranoid. Thanks


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Others may differ, but I don't think that is a problem. Out of curiosity, see if there is any voltage in the aluminium by placing your probes about a foot apart on the bare hull and in other places such as motor mounting bolts and hull etc. If you have a zinc attached,(and you should) to the hull check there too. You might try touching the two probes together as well.
 
So one question for you when they put the battery switch on is it attached directly to the boat? if it is you may want to put plywood or starboard and mount it on that ive seen the terminal just barly touch the back of where it was attached on to the alum. Any electrical connections touch any part of the alum. will get you "hot" check your grounds as well and blocks..

Good luck
 
The battery switch is mounted directly to aluminum. I did already look at that and don't believe there is an issue there, but may use the starboard idea as a precaution. Will also try the other recommended tests. I know that the hull will have continuity with the negative on the battery due to the outboard being bolted to the hull. Are the numbers I am seeing a result of that? Are these readings tolerable or not?
 
I had intermittent electrical issue on my aluminum boat and one of the repairs was to isolate the battery switch and bus bars from the metal. I placed wood blocks between the metal and electrical components. Been fine for years since.
 
firelight said:
I had intermittent electrical issue on my aluminum boat and one of the repairs was to isolate the battery switch and bus bars from the metal. I placed wood blocks between the metal and electrical components. Been fine for years since.
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^^^ This and likewise what Wolf suggested.

Make sure nothing is grounded to the hull. All the electrical should be isolated and wired as a complete circuit so to speak (I'm not very electrically inclined either). I don't personally think you are being too paranoid. One can never be too paranoid when it comes to electrical strays on an aluminum boat. If you have one that's running through the hull for some reason or other, that's what eats them.

I'm looking into the same thing right now as I have the mill scale "pocks" going on around my swim grid (little irregular pop off flakes on the surface). I think it's the big stainless mounting plate I have on the motor that is not isolated properly. This isn't a serious corrosion thing just a cosmetic thing.

Try calling Mike at the HC if it's driving you nuts. He may be able to check it out for you.

Cheers,
John
 
Out of curiosity, why would you not want the hull to be grounded?
It seems to me that you should bond the hull to the neg terminal to ensure equal potential through out. You should not attach any ground wires from any electrical equipment to the hull as you don't want to use the hull to carry any current. Btw, the hull is probably connected to ground through the motor anyways. The motor block is grounded and with all cables mounting bolts etc.. to the hull. I would attach a bond strap from the hull to the neg bat terminal to ensure a good electrical bond. This will make sure that if a Pos wire ever contacts the hull, a fuse would blow immediately saving damage to what ever device it was powering. Also, the op stated that he measures 50 mv between neg and hull. It's this difference in potential that causes current to flow. By bonding the hull to neg there is no difference in potential and no current can flow. Another point is that with a bonded hull you reduce the possibility of static charges that build up between isolated systems. That's a good thing especially while fueling.

Edit - Thinking about this a little more I realized that it may be better to bond the hull to the motor block instead of directly to the neg bat terminal. This would eliminate any possibility of parallel current flow to the starter. Anyways, I'm not an engineer, these are just my 2 cents.
 
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If your boat is electric start there 's a 99.9% probability that the motor is grounded to the hull.

On a side note :-

If you happen to have the aluminum boat sitting on bunks that are carpeted over pressure treated wood..and.....the bunks are damp, the voltage will be created automatically.

Pressure treated wood contains metals in the solution they use.

So when your carpeted bunks are damp (and they stay damp for quite some time where they make contact with the hull after you haul a boat out) then you have voltage going on.

Even if you rinse them with fresh water you will still get voltage because they are damp.

My last boat I could check with a voltage meter with no battery in it and nothing turned on (just sitting on the trailer) and I got readings all over the place.

That boat, the hull got eaten out right where it sits on the carpet bunks.

The trailer I have now I took the carpet off the wood and put those plastic isolator blocks down each side. The new boat does not contact carpet or wood.

This may not address your problem but it is certainly something to look out for....


Check all your zincs too........some aluminum hulls have extra zincs....not just the ones on the engine......
 
There is a way to ground the motor to the hull but it is not practiced very often and is a major pain in the azz. They talk about it on the Aluminum Alloy Boat site http://www.aluminumalloyboats.com/index.php?sid=24bc04a4292feb359e249ebf0ee58b79 but again it is not practiced very often.

You do not want anything grounded to the hull. Everything is run to the batteries and then ran from there. A complete loop so to speak. All negatives and grounds to the batteries and all positive from there. Everything is isolated from the hull with starboard or UHMW type material. That is how most aluminum boats are wired. You don't want any current through the hull. The reaction with the salt water will eat it. Hot docks are something to stay away from as well if you don't have proper bottom paint.

I know this all sounds negative lol. Not meant to be. Aluminum is an amazing boat material. You just have to do your homework on it to make it last a lifetime :).
 
Nothing on the boat is directly grounded to the hull. Either goes to a bus, which has a 6ga cable to the battery, otherwise devices are grounded directly to the battery. I ended up putting starboard behind the battery switch and fuse panel/bus today. Also, the trailer does have the ez loader glide bunk covers so it doesn't sit directly on carpet. Sculpin, I will take a look at that sight, but I believe the engine is grounded to the hull by being bolted to it. Is .05V really a concern? Or 10-15 milliamps? I know if I was seeing 12V on the hull, I would have a serious problem. Am I chasing my tail looking for a non issue here? I appreciate all the suggestions and ideas from everyone.
 
your engines have a negative and positive cable running to the battery switch and the battery, that is the grounding you should be worried about. electrical grounding is not the same as mounting your engines on the hull. I can't understand where you are testing for current. the only way to check if your boat is 'hot' is with a silver anode probe and a mulitmeter and you will have to have your boat in the water to do this.

one of the most common problems is with the bilge pump wiring corroding and in contact with the hull. that should be the first thing you check out.
 
Positive to engine comes from battery switch, negative goes to battery post. I am reading the current with multimeter on negative battery post and side of the hull. I also checked this while on the water this weekend and the readings are the same. Bilge pump wires are not in contact with the hull. I am not sure what a silver anode probe is.

reelfast said:
your engines have a negative and positive cable running to the battery switch and the battery, that is the grounding you should be worried about. electrical grounding is not the same as mounting your engines on the hull. I can't understand where you are testing for current. the only way to check if your boat is 'hot' is with a silver anode probe and a mulitmeter and you will have to have your boat in the water to do this.

one of the most common problems is with the bilge pump wiring corroding and in contact with the hull. that should be the first thing you check out.
Click to expand...
 
big.griff said:
Positive to engine comes from battery switch, negative goes to battery post. I am reading the current with multimeter on negative battery post and side of the hull. I also checked this while on the water this weekend and the readings are the same. Bilge pump wires are not in contact with the hull. I am not sure what a silver anode probe is.
Click to expand...

go here: www.boatzincs.com

not to sure your measuring anything of consequence by doing what you are doing. a hot boat can only be determined using the corrosion reference electrode. that also assumes you have a galvanic isolator on your AC circuit, assuming you are mooring and plugging in.

I would also check around to see if you have any paint blistering because of stainless screws/rivets in contact with your aluminum. often times they are installed without isolation washers. this is not a big deal but will eventually lead to paint blistering.
 
reelfast said:
go here: www.boatzincs.com

not to sure your measuring anything of consequence by doing what you are doing. a hot boat can only be determined using the corrosion reference electrode. that also assumes you have a galvanic isolator on your AC circuit, assuming you are mooring and plugging in.

I would also check around to see if you have any paint blistering because of stainless screws/rivets in contact with your aluminum. often times they are installed without isolation washers. this is not a big deal but will eventually lead to paint blistering.
Click to expand...

I am really just trying to see if I have any stray current on the hull from the electrical system. Although I should be checking zincs and corrosion protection like you have mentioned, I believe they are two seperate topics.
 
using the corrosion reference anode is going to clearly tell you if you have any current leaks on your boat, that's what it is designed to do. I am going to order one of these for my own use as I believe the boat that was moored next to me was hot but I want to double check that my boat is not an issue.
 
reelfast said:
using the corrosion reference anode is going to clearly tell you if you have any current leaks on your boat, that's what it is designed to do. I am going to order one of these for my own use as I believe the boat that was moored next to me was hot but I want to double check that my boat is not an issue.
Click to expand...

Ok, I will read up on that a little more. For $125 it might be worth it's while. I forgot to mention I do not moor my boat or have ac on it. It may spend a couple nights a year in the water at the most.
 
I just order the corrosion anode, probably the only way to tell if I have a DC leak on the boat. your measurement is puzzling but I honestly don't know what you might have been measuring. from what I have read, the anode is the only way to tell if there is a problem. my port side zincs were losing ground pretty fast this last season and I suspected the poorly cared for old boat next to me. I spoke with the harbor master but he wanted me to insure it was not my boat, a reasonable request, so when the anode arrives, i'll round him up and have him come down and give me a hand making the measurements. this is one of hazards of mooring, uncared for boats with owners who are not present, a real pain.
 
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