aluminum hull corrosion

[gokudl3]

I am in the middle of a boat restoration. I pulled the floor and there was foam underneath most the floor. After thinking wether or not i should remove the foam i chose to rip it out, after i pulled the foam i saw the aluminum was carroding . This explains why i had a pinhole leak near the back and why there are some bad patch jobs on the hull. When i looked at the boat this spring when i bought it i notice the hull had some repairs but they looked like attemps to seal rivets, when i asked if it leaked he said no and i couldnt see any signs off corrosion. I asked if it was in saltwater because it had a florida measurement sticker on the boat and he said no. Anyways, whats the best way to stop the corrosion? If i clean it real good shoud i use guvit on it? i guess i will feel good if i could stop the corrosion.

[rolmops]

I have never seen it happen in fresh water, but it does not have a Florida measurement sticker on it unless it was in Florida and probably in salt water.

The usual way to prevent and stop corrosion is by attaching sacraficial anodes (a block of zinc) to the lower unit. This will pick up the electric charge from between the boat and the water, the anode will corrode to the point where it needs to be replaced.

A complete layer of gluvit will stop the leaks,but you should first investigate whether any battery acid has ever been spilled on the inside and make sure to completely clean the inside, or the corrosion will just continue on the inside.

If you use Mozilla Firefox,you should google "aluminum boat corrosio" in the google on the left hand top of your screen and you will get a long list of reasons why, how to stop it,and how to repair. or go here:

http://yachtpals.com/how-to/electrolysis

Good luck.

Cornelis.

[gokudl3]

The boat does have a anode, I did clean it good and am going to clean it again, I took it to the car wash and scrubbed it with a wire brush. I filled the boat up to the waterline with water and it didn't leak so as long as it doesn't deteriorate more then it should be ok.

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[rolmops]

Some things may help you prevent further deteriation. Things like disconnecting the battery while the boat is docked.Another thing is the power cable that goes to your boat while it is docked. That cable connects you with every other boat that is hooked up the the power system and if there is only one boat with a "leaking " power system,every other boat on that grid will have increased electrolysis,which is ionizing the metal that is connected in one way or another to the water.

Gluvit stops the leaks ,but not the electric discharge which will go through your engine to the inside of the boat.

the safest thing to do is to pull your boat out of the water and make sure that there are no electric currents however small, coursing through your boat.

Something just crossed my mind. You mentioned earlier repairs. If the rivets used to do the repair are made of a material that has a different ionic charge compared to aluminum,they may be part of the reason for corrosion

[gokudl3]

How do I check for currents?

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[jimski2]

http://www.marinetteboat.com/forum/yaf_ ... osion.aspx

A lot of stories on aluminum corrosion problems. Aluminum boats do not use "zincs" but use a magnesium alloy as a sacrificial anode.

[gokudl3]

Here is a example of the corrosion, the second picture is what was under foam. First one is in the back of boat near the plug were there was no foam

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[jimski2]

It does not look like galvanic corrosion which are scales and pits on the outer hull. Could be a battery acid deal. I would inform the manufacturer on how they would handle this problem.

[rolmops]

It does not look like galvanic corrosion which are scales and pits on the outer hull. Could be a battery acid deal. I would inform the manufacturer on how they would handle this problem.

That is very true

[Shakemsam]

This past year I replaced the floor in my "73"16' starcraft. Original foam was waterlogged and for how long, who knows??

I had the same corrosion and pitting. I wire wheeled the areas, cleaned with acetone, and then used Gluvit. In areas of heavy pitting, 2 coats.

I did have a couple pin hole leaks where I used an aluminum patch stick that you apply with a torch. Love this stuff, I used it on 24 Crestliner Sabre HT, plugging old transducer screw holes inn the transom with never a problem. As far as the anode thing, If your boat is a trailer queen, or if you don't use shore power, I wouldn't bother. JMHO

[LongLine]

Was that foam ever wet? Any smell?

Gasoline is non-conductive. 10% blends are conductive. If any sits in the bildge a galvanic cell will be created. When you get it fixed, keep the bildge dry.

Very important to check all grounds. Get them back to the battery (hence the engine) & not to the hull.

Tom B.

(LongLine)

[gokudl3]

the foam was wet for sure because i had a water issue i think from my livewell...When i lifted the foam, underneath there was a white residue like a calcium deposit or something. It was only where the foam was, down the middle of the hull there was no foam and it just has the little pits in that area. In the second picture where the corrosion is happening, that is where all the white stuff was. I pressure washed it off the other day the today i went out with a wire bit on a drill and there was still white resdue that i was able to get up with that>

[LongLine]

Looks like a bingo. The white stuff was most probably aluminum oxide which is its predominant corrosion product. You're going to have to clean it well, dry it then protect it. Do a search on aluminum corrosion protection. (boats & aircraft) I'd get all the foam out then when reinstalling new foam make sure there is a good heavy continuous layer of plastic sheet between the foam and the hull.

I don't know how your gas tank is set up but mine is a permanent one mounted in the bow. The rubber gas line had been run beneath the floorboard in the foam. I had to replace it when I smelled gas one day while uncovering the boat. What I did was run the new hose thru a cemented PVC pipeline, with 45 deg elbows on the ends, above the floorboard, tight to the bulkhead. (Prevention rather than cure.)

If you have a portable tank i.e. 6 gal metal type, I'd make sure it sits on a piece of wood with painted underside and not directly on the bottom of the boat in case of overfill, leakage etc.

Definitely look at all grounding but also look for any gas leaks/spills etc.

Good luck with it.

Tom B.

(LongLine)

[Shakemsam]

I would advise against the idea of plastic between the foam and hull.

Water under the floor is unavoidable and it is important to allow air to dry it out.

When I installed new foam, I laid it so it only rested on the ribs, allowing almost an inch between the foam and the

hull. This allowed air to circulate and water to run all the way to the transom drain and bilge, without obstruction.

FWIW, I used the 2"blue foam sheets from Home Depot along with pool noodles where I could fit them.

[gokudl3]

This may sound stupid but I didn't plan on putting foam back in unless it's for strength. If its only to keep boat afloat incase it flips I don't care, I will be swimming in.

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[Big Dave]

This may sound stupid but I didn't plan on putting foam back in unless it's for strength. If its only to keep boat afloat incase it flips I don't care, I will be swimming in.

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Shore is a lot further away than it looks!!! If the water is cool or worse yet cold you won't get to far. The idea is to climb out of the water on the hull so you don't get hyperthermic. The water dosen't have to be very cold to do this

[LongLine]

Foam in a boat is more for keeping the boat somewhat afloat in case you get swamped not if you flip. i.e. over the transom or you nose dive. On a quick flip, chances are that an air pocket will form between the hull/water line & you'll get hurt.

Not a good idea to plan on swimming to shore in Lake Ontario. I would not advise that strategy.

The object of the plastic is in case the foam does get wet, it won't sit against the hull as it dries. (If it ever dries)

Also it would help if you make sure to pull your drain plug after every retrieval. (sp)

Tom B.

(LongLine)

[gokudl3]

I never plan on swimming, I would probably just float till I hit shore. Seriously though, that's no joking matter. Thanks guys

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[Shakemsam]

The foam also provides a leveling surface for the floor.

[rolmops]

There is also the legal aspect and the insurance coverage to think of. Never mind the cost of having to raise the sunken boat from the bottom and having to have it brought to port,which are things that you have to do by law.

On another note, if you use a good pourable foam that produces closed cells, you don't have to use plastic to cover the bottom and you will have a much safer boat which is nice if you want to bring your wife and kids on board. for a trip.

[gokudl3]

Enough said....foam it is. I never thought of the unsinkable boat part, especially with the corrosion. Is there anywhere locally to get this foam and what is it called? Thanks guys, I just can't wait to get it done! Sooner the better, the niagara is calling my name.

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[GAMBLER]

West Marine carries it. You mix it and poor it. It really expands once it is mixed and poored. Make sure it has room to expand.

[Excavtr]

I just had a hull repair done and filled it with foam last night. West Marine has it, but you will overpay for it. I found it at Clark Craft in Tonawanda for a fraction of the price.

http://www.clarkcraft.com/cgi-supplies/ ... 37820a362d

I had pretty good results. They say optimum temperature is 80-90 degrees for application. I set the bottles next to a space heater to keep them warm so I didn't have to heat the entire shop. They say heating Part A in a microwave will work too, but I didn't like that idea.

Clark Craft sells measuring cups, you'll need at least 2 of them and a lot of disposable mixing containers. I used 12 oz plastic drinking cups. They say to use small amounts of Part A & B (2 oz each) and layer it in. I used 3-4 oz each in the 12 oz mixing cup and that is about all you'll fit. You'll need room in the cup for mixing and some expansion.

To mix it, I cut a paint mixing stick to 4", taped it to a wooden dowel and put it in a cordless drill. Pour Part B into your mixing cup, then Part A (Part A is the accelerator), and mix fast until it turns milky and starts to bubble. pour it into you cavity before it jumps out of the cup. It is pretty simple, but you have to work fast.

The small portions make it time consuming. I tried a few larger batches (5 oz each) to speed it up, but it is harder to control and I ended up with a few high spots that will have to be cut down.

Good luck!

[gokudl3]

Thanks.... Wil keep ya updated and show some pics when I'm done

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[carpedium]

I'm going to have to do all this as well at some point this winter/spring. What are you using to go back in for a floor? I was considering plywood coated in resin.