Bonding Aluminum Hull

[minuteman62-64]

Well, after reading many conflicting posts on this subject my conclusion is that I will bond my aluminum hull to the negative terminal of my battery (however, I will not be using the hull as the ground for the electrical components - each will have a dedicated ground wire). The tipping point was when I read the owner's manual for my 1982 Mariner which recommended, for aluminum hulls "...... bond the negative battery terminal to the hull using a #10 wire."

So, I'm now at the point of deciding exactly how I connect the #10 wire to the hull and what type of wire (Cu or Al) to use. Seems like using the wrong materials would create just the corrosion/electrolysis problem I'm trying to avoid. At some point you have to get from aluminum (hull) to copper (wire to negative battry terminal). However, it doesn't seem like a good idea to connect a copper wire directly to the aluminum hull.

I checked out West Marine in the electrical section and they didn't have anything specifically designed for this purpose.

Any of you aluminum boat owners have any suggestions or examples of how your bonding is done?

As always, appreciate any and all input.

 

[Silvertip]

Re: Bonding Aluminum Hull

There is no need to bond the battery to the hull but you might be interested to know that the very act of bolting the engine to the boat "creates" a bond anyway. Remember -- the engine block has the battery negative cable connected to it. Therefore when you bolt the engine to the boat, the bond is created. If you don't believe it, check it with an ohm meter.

 

[Splat]

Re: Bonding Aluminum Hull

ST is correct. However if you really want to bond it, there is a paste made specifically for combining dissimilar metals for electric connections. For the life of me I can't think of the name of it right now. I'm sure someone will chime in with it.

Bill

 

[minuteman62-64]

Re: Bonding Aluminum Hull

Concur on the bonding via the motor. However, my motor is mounted on a rubber transom pad, so the only electrical connection is through 2 SS bolts that go from the motor mount through the aluminum transom skin and maybe contact the skin by the edges of the drilled holes and through the bolts and washers clamped to the interior painted Al surface. Maybe that's one reason why the Mariner folks recommend bonding w/#10 wire?

On the paste - that's probably the stuff they sell at Home Depot for conncting Al wire to Cu wire - it prevents the Al from corroding and messing up the electrical connection. Probably wouldn't hurt to use it, although I don't know if it is intended for this particular marine use.

 

[pootnic]

Re: Bonding Aluminum Hull

"As always, appreciate any and all input."
Why do you want to do this when theres no need to?
An antenna is about the only thing to ground to the hull and you can limit the DC with a capacitor in the application.
Do you plan on attaching some type of anode?
I'd ask around or google this topic abit more before going that route.
I think your looking for trouble.
http://www.duroboat.com/experience/AluminumBoatsandCorrossion.htm
Theres many more articles on this subject,pictures as well.

 

[minuteman62-64]

Re: Bonding Aluminum Hull

Thanks for the link. Good info. It appears that a boat that spends the majority of its life on a trailer doesn't need a protective anode and bonding of the hull is not necessary.

On the other hand, as pointed out in a number of posts, the motor can provide a bond to the hull simply by the attachment to the transom (although the effectiveness of that bond may be compromised by transom pad/paint/minimal contact area). Then I have the recommendation in my OB owner's manual that the hull be bonded with #10 wire. My conclusion is that there is no down-side to a properly made electrical connection between the hull and the negative battery terminal, but there may be some benefit. So, if I can figure out a "safe" way to do so, I may go ahead and bond the hull anyways.

All of which brings me back to my original question: what does an actual "bond" to an aluminum hull look like? Anybody seen one?

I'll point out that my Bayrunner did not come from the factory with a "bond." On the other hand, it came from the factory with cad-plated fasteners, so I'm not sure the folks at Bayrunner/Westcoaster are exactly experts on preventing corrosion in an aluminum boat in a marine environment.

 

[minuteman62-64]

Re: Bonding Aluminum Hull

I now have (finally) the motor re-mounted on the transom. Checked between the negative lead coming from the motor and the hull with my ohm meter. No electrical continuity - likely because of the rubber transom pad and liberal use of sealant in the mounting bolt holes.

So ..... based on my readings on this site and on a forum devoted to aluminum hulls, and the motor mfg. recommendations, I'm going to bond the hull via one of the interior bulkheads (that are welded to the hull). I'll also be installing an aluminum anode based on my conversation with staff at Boat Zincs, Inc.

I'll let you know if my boat begins to dissolve

 

[Grandad]

Re: Bonding Aluminum Hull

I think you're doing the right thing by bonding the hull. The fact that the hull "may" be bonded by the motor or by any metal component that is also connected to the battery negative means that the accidental bond is likely a poor conductor. In my experience as an electrician, poor connections that carry even small electric currents tend to cause "noise" on the electrical system that can interfere with the normal operation of electronics, even if they themselves are correctly connected. A soundly connected wire bond avoids the possibility of any intermittent connection. And of course, never use the hull as the return path for power to electrical equipment.

As to how or where to bond; as long as the connection is not made in a damp location, I don't think you'll have a problem connecting a copper wire to the aluminum hull via a simple crimp connector. If you want to use an anti-corrosion paste, there's a product called Noalox that can be used on the aluminum at the terminal. - Grandad
http://www.idealindustries.com/prodDetail.do?prodId=noalox

 

[Fed]

Re: Bonding Aluminum Hull

It's a real can of worms minuteman, what happens if you get a bad connection at the main engine block negative?
Assuming your engine to hull will have some continuity in fact it's hard to imagine no continuity with 4 big tight bolts holding it on.
If I was putting a motor on I'd be thinking that it will be impossible to insulate it from the hull so might as well make it a damned good connection.
Anyway, would your motor still start & run via the hull to battery connection?
I've never owned an aluminium boat but my gut tells me there should only be the one negative wire on the battery, forgetting accessories.
I have a mate who's dissolving his Yammy anodes & skegs at a great rate of knots & he tells me the anodes are working because they disappear so fast.
Interesting thread, let us know how you go.

 

[minuteman62-64]

Re: Bonding Aluminum Hull

It's a real can of worms minuteman, what happens if you get a bad connection at the main engine block negative?
Assuming your engine to hull will have some continuity in fact it's hard to imagine no continuity with 4 big tight bolts holding it on.
If I was putting a motor on I'd be thinking that it will be impossible to insulate it from the hull so might as well make it a damned good connection.
Anyway, would your motor still start & run via the hull to battery connection?

Looks like the 50/50, pro/con debate continues

My engine is an older (and smaller - 30 HP) one - fastens with two screw clamps that ride on the rubber transom pad and two bolts that go from the engine mounting bracket through the rubber transom pad and through the transom. The holes for both bolts were liberally dosed with sealant. Thus, I think, the electrical isolation of the motor from the hull.

Under these circumstances, if there were no battery negative to engine block connection there would be no closed circuit from the battery to starter motor and back to battery. So, I think the answer is that the motor would not start w/electrical starter (although it should manually start).

 

[MH Hawker]

Re: Bonding Aluminum Hull

that compound is called Penetrox

 

[old boat 54]

Re: Bonding Aluminum Hull

Don"t see the need in bonding (-) Negitive of battery to hull. I agree, if you have an electric starter, and
negitive cable is bonded to motor, usually heavy bracklet or case of starter, you may in fact have contact of negitive through
motor clamp or bolts to the transom. However, unless there is another wire to flow current it should not matter.
There is no reference to "ground". This is an isolated system.

As far as flowing a small leakage current from another component ( lights, bilge pump motor,ect.) though its negitive wire,
this would mean that device has a second unintended connection, to negitive other then it
intended termination. In other words, a wiring problem, such as a chaffed insulation on the negitive wire from say,
your bilge pump rubbing on the hull bonded to the negitive of battery, could cause the device to still
work intermittently, but not properly, and could cause heating at the point of contact, as it would be a poor
connection. If the hull was NOT bonded to negitive, the chaffed negitive wire, could not find a return path
through the aluminum hull, and the device would not work at all. This would cause someome to investigate
the problem, and not say, "Yeah, the pump will work, when I hit a couple of more wakes, I think I have a
loose connection somewere and need to find it ... someday."....

Sorry the way these text line are seperating, I might have hit a tab key or something.

 

[Fed]

Re: Bonding Aluminum Hull

Have a look at this thread old boat.
http://forums.iboats.com/showthread.php?t=515303&p=3477020#post3477020

I'm not sure how it will pan out yet but it's looking like a problem caused by a bad negative connection to the block combined with a secondary ground connection to the battery via the hull. Messy stuff.

 

[old boat 54]

Re: Bonding Aluminum Hull

Fed,
Pictures a little tough to see, but from reading post's, it sounds as a heating problem on a secondary ground path through the hull. Keeping the connections clean and tight is important, as you know. Hoping things are good down under.

 

[Grandad]

Re: Bonding Aluminum Hull

There is no reference to "ground". This is an isolated system.

I disagree oldboat. This is not an isolated system. You can't get a much better opportunity to create a ground referenced system than an aluminum hull between a body of water a metal boat motor that is directly connected to the negative battery post. Yes, you might solidly wire the negative path to all your loads so that the current doesn't normally flow through the hull, but you can't avoid the possible path through the hull for accidental shorts between either the positive or negative conductors.

Intentionally bonding the hull ensures that the unavoidable path through the hull back to the battery will have no appreciable resistance. If a positive wire shorts to the hull, a fuse blows faster and protects better. A poor bond on the hull provides a high resistance path and short circuit current will flow through the hull for a longer period, possibly indefinitely, opening the door for corrosion at every metal joint in the path. - Grandad

 

[kahuna123]

Re: Bonding Aluminum Hull

From the salt water side of things. Everything on, under, or in the boat that was metal that came anywhere near water was bonded with no 6 copper wire ( green). Keeping everything the same bond potential (not ground, bond). Air conditioner pumps, rudder post, shafts, toilet plumbing, thru hulls. Then only at one point was it brought back two places. To a galvanic isolator to the neutral wire of the shore feed and to the ground of the boat.

Hatteras went so far on the trawlers they built to add transformers at the shore power to insure no dc got buy. At one point which was a good idea Bertram and Hatteras broke the negative and positive at the breaker box when someone had the power shut off to a circuit. Never had a problem with that system.

But for a trailer boat in fresh water its really overkill.