Hull Zinc

[minuteman62-64]

New here, so I hope I've got this in the right section.

I have a 1982 Bayrunner, 15'6" long that has been sitting idle for about 20 years. As my retirement project I'm putting it back in service. One thing I noticed when surveying the situation was some pitting and one "pinhole" (~1/8" diameter) in the aluminum transom skin. I'm guessing that part of the problem is that Valco/Westcoaster saw fit to use cad plated fasteners throughout the boat, including many on the transom. I'll be replacing these with SS.

My questions are w/regard to bonding and use of hull zincs as a further protective measure.

First, if I make sure the outboard motor is in good electrical contact with the hull (with a dedicated bonding wire/strip if necessary), will the zinc anode on the outboard suffice to protect the aluminum hull? Or, do I still need a separate zinc mounted on the hull? I should add that the boat is trailered and, even when back in service, will spend 80% - 90% of its time on the trailer. I should also add that when the boat is in the water the motor is in the down (running) position at all times.

Second, given the condition described above (motor in good electrical contact with the hull, etc.), is it still necessary/desirable to have a dedicated bond to the hull?

Third, am I headed in the right direction w/regard to preventing further corrosion of the aluminum hull/transom.

Appreciate any and all input.

[IronwoodIsland]

Hello Minuteman

Sounds like a pleasant retirement project. Does the transom have any wood in it? Aluminum does not like wet wood against it, this can promote corrosion. Was your pinhole below the waterline or just next to the bolts / brackets? Steel or Stainless Steel bolts will both result in local corrosion around them. This can be avoided by using Tef-Gel or teflon paste in the bolt hole and nylon washers under the bolt head and nut to isolate the bolt from the hull.

Re: Bonding - most motors have a bonding wire between block and bracket so yes, the engine is grounded to the hull. The little engine anodes only have enough area to protect the engine so a seperate anode is advised for the hull if it is going to spend much time in the water.

Some pictures of the corrosion would help determine the cause.

Happy Boating!

[minuteman62-64]

Yes, the transom does have a 1" thick plywood reinforcement. I have used a liberal application of the Rot Doctor's CPES penetrating epoxy to attempt to saturate the plywood and hopefully stabilize some dry rot and minimize future water absorption.

I'll post a photo as soon as i figure out how to do so.

[Katoh]

Minuteman
Pictures would be good, everything IronwoodIsland said is pretty much spot on.
Can you replace the ply with a sheet of Aluminium? it would solve the problem of having wet wood up against the hull.
I have found during the course of restoring my boat, in places were trapped moisture was allowed to sit up against the aluminium, was always going to create a corrosion spot.
On the subject of bolts through hull or even rivets use some Duralac on them, that will create a barrier between the metals. As far as Zinc's go I would put a zinc on the hull, the motor zinc's are calculated and positioned to protect the motor, not the whole boat.
Give http://www.boatzincs.com/ a ring or email, tell them what size boat and they will advise you how much and were to place the hull zinc. They worked all that out for me.
Good Luck and happy Restoring
Katoh

[minuteman62-64]

Thanks for the referral to the Boatzincs folks. I got an immediate response to my e-mail and called and talked to Bob - very helpful.

Bob recommended the aluminum type anodes for my application and gave me a half-dozen options. He also discussed the pros and cons of anodes, attachment, corrosion issues in general, etc.

The one thing he suggested, which seems to run counter to most (well, about 50% at any rate) of what I've read on this and other sites, is that bonding is not a good idea for a boat of my size (15'-6") and use (trailered, way more time out of water than in). His reasoning was that the gains from the bonding were more than offset by the risks should there be a ground failure on one of the electrical components, resulting in the hull providing a direct path to ground for that component.

[welder]

The BoatZincs banner up top is a Click able link striaght to www.BoatZincs.com

[Katoh]

The one thing he suggested, which seems to run counter to most (well, about 50% at any rate) of what I've read on this and other sites, is that bonding is not a good idea for a boat of my size (15'-6") and use (trailered, way more time out of water than in). His reasoning was that the gains from the bonding were more than offset by the risks should there be a ground failure on one of the electrical components, resulting in the hull providing a direct path to ground for that component.

Actually that's very interesting, So to be correct you should not put a bonding wire from hull to anode and just use the weld from anode bracket to the hull as its bond, if I read that correctly?
Cheers
Katoh

[minuteman62-64]

He was referring to an electrical bond from the battery negative terminal to the hull, as not recommended for my particular situation. This is what I was mentioning as an area of seeming controversy/debate.

He stressed very strongly the need for a good electrical connection between the anode and the hull - either by direct contact between the anode and hull or via the anode mounting bolt and hull. Although we didn't discuss it, I presume a bonding wire from the anode mounting bolt to the hull would also satisfy this requirement.

[welder]

On a alloy hull a GOOD electrical connection is created when the anode is bolted CLEANLY to the hull , there are NO wires needed from the anode to the hull .

On a STEEL hull the anode is welded on , the straps are cast through the anode.

With ANY anode a CLEAN mounting connection is needed. You should be able to pull the bolted on anodes and CLEAN them as needed and of course when any anode is about 50% gone it NEEDS TO BE REPLACED.

DO NOT use a STEEL WIRE BRUSH to clean your anode or your ALLOY ......EVER

There are pros and cons of connecting your battery [ Negative ] to your hull . Most manufactures will NOT ground the hull this way and that is a whole nether story.

[Katoh]

He was referring to an electrical bond from the battery negative terminal to the hull, as not recommended for my particular situation. This is what I was mentioning as an area of seeming controversy/debate.

Thanks for clearing that up. it didn't quite sound right. The part about not bonding the negative to hull I can see being controversial, could be done on an outboard but mine is an inboard.
I think I might give him a ring, to get some explanation as to why.
Cheers
Katoh

[welder]

Katoh, it doesn't matter weather it's a IB or OB for the debatable said hull grounding.
One problem with grounding to the hull with a proper size ground wire [ Read BIG wire and SOLID connection ] is IF you loose a ground on a widget on the boat and that widget is looking for a return path to the battery , it may use the hull/boat to complete the circuit .
Keep in mind , you are sending 12 Volts out and 12 volts has to come back to make things work so if the hull is the return...You are heating up your boat.
Now you are good with your boat as a ground and you pull in to a slip and the guy next to you is bleeding 12 Volts in to the water , it wants to go somewhere , guess where it's going and guess what it's going to do to your zincs then your hull.

This could be just one problem with grounding a hull/Battery.

[Katoh]

I have always been a big believer that the electrical system should be total isolated from the hull, but When you read what the professionals say is to keep the electrical system isolated and to also make sure you have a good connection from negative to hull. They also say there is no possible way to totally isolate the neg from the hull, just in the areas in the motor, were the neg is grounded anyway, leaves a connection to the motor which in turn is bolted to the hull, given a neg connection to hull.
This is my concern at the moment, as I am trying to repair holes in my hull caused from stray currents. Is it better to bond than to isolate and have the zinc's eaten away maybe quicker? Or to try and totally isolate, motor and all.
References For bonding the Neg to boat.
viewtopic.php?f=3&t=2262&p=18471&hilit=kmorin#p18471
Boatowner’s
Illustrated
Electrical
Handbook
Second Edition
Charlie Wing
I dont have a reference for not bonding the neg!

Katoh

[minuteman62-64]

I've been wrestling with the same "bond or no bond" issue and trying to resolve the conflicting info. My boat didn't come from the manufacturer with a hull bond (of course the good folks at Valco/Westcoaster also saw fit to use ordinary steel fasteners in what was designed as a salt water boat - so I'm not sure they are the fountain of knowledge on electrolysis/corrosion issues). About half of the local (San Diego) owners of similar boats that I have talked to have installed a bond - some directly to the anode bolts. Also, my outboard motor user's manual recommends, for aluminum boats, running a #10 wire from the battery negative directly to a point on the hull.

My current thinking is:

The outboard motor frame is directly connected to the battery negative terminal via the battery cables.
I do not think I can achieve a total electrical isolation of the motor from the hull.
If there is a connection between battery negative and the hull, via the motor, it is better to have a good electrical connection.

So, right now, I'm thinking a dedicated bond to the hull is the way to go. Next week, after I've read some more opinions, I may be headed in a different direction.

[Katoh]

Hi Minuteman
I am thinking the same as you, and are basically in the same predicament.
I bought my boat as a project rebuild, which already had the holes in the hull. From what I could see from the original build it was done all correctly. firstly my boat has an inboard diesel, and what the builder did is from the neg side of the starter motor run another cable of the same size to the hull, then separately ran another large wire from the engine block to the hull.
I think the previous owner caused the problems as they installed some lights but used the hull as the negative feed, They only ran the positive cable to the lights.
But also there is no evidence of a hull anode on the boat, so I will be adding one.
I will be doing a total re-wire on my boat, I am just not up to that stage yet, at present I am looking for as much information as I can on this subject, and I have asked the question on another forum to gage other opinions.
I will keep you in the loop.
Cheers
Katoh

[Katoh]

Minuteman
After talking to others and doing a lot of late night reading, has bought me a little more information.
It is nearly impossible to isolate the negative from the hull if you use a motor with electrical attachments, Eg starter motor.
The motor is negatively bonded and once bolted to a hull the hull is bonded as well. Even through steering, throttle and trim mechanism is a conductive path.
The bigger more important part is this, we need a good bonding wire from motor to hull, or anything else that bolted on to the hull. This is so we dont get an electrical potential difference between parts. With good bonding we should have electrical equilibrium in the hull and its parts, we should not have any trouble thereafter.
I would not run a cable from battery or the negative bus directly to the hull, this should be done from the motor. I would consult your motor user manual or contact the manufacturer to see were they recommend you place the Bonding wire.
If I find out more I will post the results.
Katoh

[minuteman62-64]

The results of your research reinforce my current thinking to bond. Electrically, I don't think it makes a difference if the bond path goes through the motor to the hull or directly from the battery negative to the hull. There may be a physical connection issue that would push towards using the motor pathway. My motor (Mariner) manual recommends a #10 wire from battery negative directly to hull. That may have more to do with protecting the motor and motor zinc from electrolysis/corrosion than protecting the hull - I don't know.

My motor will be mounted on a rubber transom pad so I'm not sure how good the electrical path from battery negative to motor to hull will be. Right now the motor isn't mounted. After I mount it I'll check the path with my ohm-meter. I've been thinking of ways to make the electrical connection from the motor to hull or from the battery negative to hull, in the event there will be some resistance shown by the ohm meter once I mount the motor.

[Katoh]

Minuteman
Personally I would not run a wire straight from battery to hull, even you said you would prefer to go from motor. From what I have gathered they say it is a redundant connection from the battery or bus, and the connection is better served through the motor.
I think were both on the some train of thought.
You said you Where mounting on a rubber transom pad, I would definitely run a bonding wire from motor to hull. I can't remember were but I also read that its good practice to run a bonding wire from anode to hull as well.
I look at my boat, it was built in 92 and has lived its life in salt. Yes I am welding up holes in the hull but they seem to be new holes and some of the wiring is new and has a lot to be desired. The original wiring is as I described earlier, and I dont think it had a problem till it was altered.
I dont know if your read my previous posts but I am in the middle of a full rebuild as well. The wiring on my boat is totally obsolete the only thing that will be reused is the motor harness the rest is all new from scratch. As you can gather this subject is toying with me as well as you.
Cheers
Katoh

[ALUMINATOR]

I have my diesel completely isolated from my hull. I even put a solenoid on the neg cable to the battery so it is only connected when I am cranking. On an outboard can't you use a plastic sleeved bolts and some more plastic at the transom to isolate it? Almost every skiff I see around here has the pin holes and I am guessing they are from stray current.

[Katoh]

Aluminator
Must have been one hard task to isolate your diesel, But can I ask why did you totally isolate it? From all I have read, the experts tell us it is better to bond all our metals with an earthing wire to give give them 0v differential potential. I can see how you might have isolated just your negative side, but isn't there a problem or you can create a problem with your alternator by doing this.
The pinholes in the other boats are they moored or trailered?
Katoh

[minuteman62-64]

I believe I could isolate the OB from the hull. The motor clamp will be mounted on a rubber transom pad. So, all I would have to do is use plastic sleeves on the mounting bolts and nylon washers under their heads. The question is: should I? Opinions seem to be about 50-50 either way

[IronwoodIsland]

It doesn't really matter too much in the case of a simple electrical setup like a small O/B on a skiff.

The important more general point is that if there is a ground to the hull it should really just be at one point, otherwise there may be current flowing through the hull which can lead to corrosion. With multiple grounds the current will be split up and the hull would take the majority since it is lower resistance.

The other issue is that unless you are using aluminum wire, getting dampness and salt on the connection of copper wire to the hull can effectively set up a half cell creating voltage and thus current all on it's own.

[Karl in NY]

I'm totally confused about choice of anode material for an aluminum hull boat.

There will be different recommendations for salt vs. fresh water, too.

My understanding is that all major outboard motor manufacturers currently use aluminum for all internal (cooling system)
anodes, not zinc.

Sooo, what material should be used as a hull anode? Will using zinc (assuming saltwater) cause the internal motor anodes to no- longer sacrifice, or will the zinc rapidly sacrifice instead?

Also, in fresh water, would magnesium be more appropriate for the hull anode on an aluminum hull boat?

I have read the Nigel Calder book and the Charlie Wing book...and have visited the two major "zinc" websites, and I'm not coming-up with definitive answers.

I really can't see changing-out the internal OB motor anodes under ordinary circumstances...but what about the external anode on the lower-drive? Zinc, or aluminum?

What I think I have learned is that aluminum anodes can apparently protect aluminum engine parts (and aluminum hulls) because the anodes are of a "lower" grade of aluminum on the galvanic scale.

Can anyone who actually knows what they're talking about shed some light on this?

[minuteman62-64]

I can't claim to know what I'm talking about on this subject, although I'm slowly getting educated through the various posts and other sources. As I previously noted, I did call "Boat Zincs" (see banner at top of home page) and talked to one of their reps. Since they sell zinc, aluminum and magnesium anodes I have to assume they have no bias towards one or the other. For my application (15'6" aluminum hull, trailered, OB power) they recommended aluminum anodes.

Bob, at Boat Zincs, was very helpful, took his time explaining what he recommended and why, and even recommended a number of alternative anodes for my application. For the price of a call to Sudbury, MA you can probably also get some good info for your situation.

[minuteman62-64]

Oops. Now I don't see the "Boat Zincs" banner at the top of the page. Bob's number is 978 841 9978.

[Katoh]

Karl in NY
One thing to remember, you don't mix and match, whatever anode you use. If you use zinc's on the motor than you use zinc's on the hull, or magnesium on motor same on hull, the same thing with aluminium.
Just to cover old ground never use magnesium anodes in salt water!
I had no choice on my boat, the motor a diesel Volvo Penta only comes with zinc anodes and there's 3 of them. I am basically bound to use a zinc on the hull and at the same grade.
I believe aluminium is now more of an all-rounder, and does quite a good job in salt water.
Good Luck
Katoh