Aluminum Boats and Crevice Corrosion

[StrikeFighter]

I have been studying a (cosmetic, not sea worthiness) corrosion problem I have been having with my 22 foot Harbercraft "Painted" aluminum boat. (Note; it is used in fresh and saltwater and zinc up very well.) The problem is paint bubbling around the rubber window molding and all fitting such as snaps were these area are on a painted surface.







(I might add were there is bare aluminum no problems) In my research thinking I was having some type of a galvanic action with my boat. I was amazed when I discovered the real answer which was simply crevice corrosion. When fastening anything to aluminum or when fastening aluminum to anything else, (Especially over painted surfaces where the paint seals out oxygen) it must be kept in mind that all aluminum alloys are subject to "crevice corrosion". What this means is that while the marine aluminum alloys will do just fine in the corrosive marine environment, the metal surface must be exposed to oxygen in order to form a protective oxide layer. Where there is a crevice, say where an aluminum windlass is mounted onto the deck, the aluminum has lost its ready access to oxygen, so cannot repair itself, and begins to freely corrode. This applies equally to aluminum alloys in the 5000 series (plate) and the 6000 series (masts, pipes, and other extrusions). Otherwise the area must be totally sealed so salt can't get under the paint. That means no breaks in the paint or cracks and/or the fitting sealed in silicon or other similar sealant.

Go to this fantastic web site listed below which really opened my eyes as to what my problems were. Also the trick to getting the windows out of an aluminum boat is real simple. If you look at the rubber molding around your windshield on one side you will notice a crack in the middle of the molding that goes all the way around the center of the molding. Take a blunt pointed awl and insert into the crack which flips back the molding lock and then push all the way around pulling the lock back such as taking a tire off a rim. The window will now be removed from the side where the molding lock has been unlocked. I'm placing the crack where the molding comes together at the top of the window really sealing it good to preventing saltwater intrusion down to the paint edge inside the molding.





See this article written by Michael Kasten on Aluminum.
http://www.kastenmarine.com/metalparts.htm

I have attacked my problem with a vigor. I'm sanding and wire brushing down to metal, using then using Prep 33 and then 1201 alodine to put a protective coating on then going with a primer then repainting. I'm using extreme care in sealing the inside of the rubber molding from saltwater penetration.



To find West Marine Alodine 1201 and Alumiprep-33 Etching Solution do a google search.
Type or cut and paste in search box Alumiprep-33 Etching Solution

I really want to thank Michael Kasten who figured out the crevice corrosion on Aluminum and wrote such a fine article. Good job Mike

I would never ever buy a "painted aluminum boat again. I certainly would have aluminum boat but it would have to be mostly bare metal. As the crevice corrosion starts under the paint where there is a break in the paint and the bubbling is caused by air expansion which lifts the paint outwards and when you see this immediately break the paint surface over the bubble so oxygen can get to the aluminum to stop the corrosion and it relieves the pressure under the paint to stop further lifting and expansion of the paint bubble until you can repair it correctly. (It don't look as good but it helps stop the expansion and enlarging bubble) Painted trim is OK but not where there is fitting, windows and thing which are the source of the cracks. Just say no to crack. When you see this type of corrosion take action immediately otherwise it will eat up your aluminum like you can't believe. This is deficiently aluminum cancer. Note: any time you see a white floury looking substance coming out around window and fitting you have major crevice corrosion going on. Put on your cape and go to work.

Another good reason not to buy a painted boat, you see what you get as they don't have paint to hide shortcuts. If you are having an aluminum boat built you should consider to have things welded on (made from aluminum) and not bolted on which is the source of many cracks.



Well one side is done, now.



(All Cosmetic, not sea worthiness) If I had a seaworthy problem, I would take it to a boat builder and have him to replace all metal thats may even remotely have been effected.

Harbercraft makes a good boat, which I'm very happy with. Since I manufacture tackle which requires me to be able to fish high mountain lakes as well as light to medium saltwater condition. This boat does an excellent job in both environments as well as light to tow with 1/2 ton pickup. Now that I know what to look for and how to overcome it, I would never allow crevice corrosion to go this far without taking corrective action. If you buy a new aluminum boat, seal everything to the tenth degree before taking it in the ocean.
I hope this little tutorial on crevice corrosion will be useful to you should you choose an aluminum boat.

“Boats suffer corrosion, but good fishing buddies gather no rust."

[IDFishrite]

Interesting,thanks for taking the time to share.

[StrikeFighter]

This is a follow up on crevice corrosion (All Cosmetic, not sea worthiness)

Crevice corrosion and galvanic corrosion or two different animals
Crevice is base on lack of oxygen with a start of corrosion that runs amuck. Other types are based on two dissimilar metals which creates a battery effect.
If you use aluminum accessories rather that stainless are steel accessories then have them welded on which will prevent the cracks that allow crevice corrosion to eat away at the aluminum.

Example having a piece of wood bolted to aluminum is the worse thing you can do. The saltwater will penetrate the wood and go down to the aluminum and immediately start crevice corrosion (no oxygen) under the wood which will eat away the aluminum completely over a short period of time. It doesn't matter if it wood, plastic, stainless steel, steel or rubber. Especially paint where you drill a hole to put a gadget or snap on and you have broken the paint with the drilled hole, which allow the saltwater to penetrate to the bare aluminum and starts the crevice corrosion which block off access to oxygen. The corrosion will start spreading and as the sun heats up the air bubble and corrosion gases will lift the paint outwards as you will quickly see paint bubbles. When you do immediately break the bubble of paint to stop the outward expansion of the corrosion bubble and allow some access to oxygen to stop or slow down the crevice corrosion until you can get to the repair. (Critical prevention)
When first putting on a new fitting or snap, prime an paint the drilled out hole and set the fitting (totally, under neath and where screw is) in silicon so saltwater can't get to the bare aluminum to start the crevice corrosion process or have the fitting made from aluminum and welded on.

Aluminum most have ready access to oxygen to heal itself or be completely sealed from salt water to prevent crevice corrosion.

This was my problem, for some reason I just couldn't under what was attacking the aluminum under the paint and around my window. I thinking, maybe not enough zinc, battery ground problem, leaving the battery on when setting, all the while simple crevice corrosion was consuming my boat like a pirana.

Now mind you the outside paint and the hull hasn't been effected at all even those most of the outside is painted, because the only fitting there are where the overflow and intake hole fitting are.

If I was having an aluminum boat built then I would want everything thats possible made out of aluminum and very skillfully welded to the boat. No paint except on the outside for trim look purpose, but no paint where any through hull fitting, windows, windshields, screws or where cracks could be created. No to Crack! such that are created with after market accessories.

Note; Skillfully welded mean just that inspect every welded on fitting, window frames and etc. for any defects in the weld which can allow saltwater penetration under what you welded on. If you welded on an aluminum cleat and there was a break in the weld, you just created a crack under the cleat where crevice corrosion will consume that base metal and aluminum cleat.

(All Cosmetic, not sea worthiness) Should you have any type of sea worthiness problem, take it to a professional boat builder who has all the knowledge and equipment to repair your boat properly for your safety.

[boater]

probly one of the best posts ive ever read about this problem, the only thing i would do diferent is about my next boat, it will not have a drop of paint on it the only thing it will have for looks is vinyl.

[backlash]

Just out of curiosity, what year is your boat? I have had my Alumaweld for over 5 years without a sign of corrosion, and trust me, theres been plenty of salt on it. A co-worker of mine is experiencing the same problems as you on a Weld Craft, its about 5 years old as well. There must be something to be said for metal prep before paint. Great info.

[StrikeFighter]

It is a 2001 Harbercraft. No doubt that there was a shift change about the time the prep was going on this boat. Prep work with aluminum painted boats is critical to long life. I complain about when it started, they were clueless and did not want to help at all. Thats why I have taken the effort to pass this info on. Had I known this when I was ready for a new boat I wouldn't be dealing with this today. The quicker you jump on these cosmetic problems the quicker you will learn how to prevent them and as I will~~~~ slowly remove and reinstall all accessories with the proper prep work for long life.

I like my boat, but there is a fine line between liking a boat, liking to fish on a boat and liking to work on a boat.

“The charm of fishing is that it is the pursuit of that which
is elusive but attainable, a perpetual series of occasions for hope”

[aye fsh]

I have a 2000 NR that's exhibiting exactly what you have shown here.
D A N G !
Maybe I'll just get her blasted and be done with it. Thanks for all the research and bringing it up here, BIG help.

[garyk]

Thanks, I've got a 2000 Hewescraft with some small (<1") areas like that under the vinyl hull decal. All the problems are at the edge of the vinyl (where it meets the gunnel). I think your post explains what's going on. Thanks for the useful into!

[Chrome Bumper]

Mt Hood fasteners has aluminum nuts and bolts. Since aluminum acts as a anode and protects the stainless by galvanic corrosion you might want to consider using the aluminum bolts instead of stainless where possible. Google galvanic series.

[StrikeFighter]

aye fsh

My Harbercraft would not work well for bead blasting for this reason. When Harbercraft built this boat they used a chalking compound where some welds should have been and they built up some weld area with a heavy chromate or body epoxy so that the boat would appear to look like a fiberglass boat without seeing the welds. Yours may have the same thing done. Look at the base of the window frame on the outside. If it looks smooth like a fiberglass boat and you don't see obvious weld bead, then your boat is done the same way my boat is.
If you blast it, I believe you going to unleash a kettle of worms and create some problem you didn't want.
I would consult with Harbercraft before blasting it.

I just came it from completing the job.

“If you really want something in this life you have to work for it. Now quiet, they're about to announce the salmon season lottery” Oh did you buy any ticket?

Bill Shelton
"Drive the point home and then let them go!"
Helping our fishery resources is everybody's business!

[boater]

northrivers do have green stuff around the bottom of the window frame, i personaly think its a waste of money and time, why not just lay down a good weld and paint over it ?

[KChookem]

I wonder if "Corrosion Block" type products would help prevent this problem?

On my non-aluminum boat, primarily used in saltwater, I use Corrosion Block on top snaps, pop rivets, cleat fastening screws and other dissimilar metals and it seems to help.

[aye fsh]

Yesterday afternoon my curiosity got the better of me. Recent posts regarding soaked foam prompted me to pull the floor boards and check it out. Of course, between the foam and the hull there is the crevice corrosion. Doesn't seem like the best idea, putting foam in there that creates an anaerobic environment. I've always rinsed my boat after running in the salt, but there's no way I ever washed it good enough to get all the water between the foam and hull flushed.

Looks like I have a project ahead of me, ugh.

[StrikeFighter]

Sorry to here that. Some how you might figure a way to keep the flotation foam but that it has a ready access to oxygen so the aluminum can repair itself. Do you have a picture that others can see what problems they should be on the look out for. I'm going to pull my floorboards soon and look the gas tank over.
Perhaps there is a warranty coverage on that from the manufacturer.

The only people with whom you should try to get even are those who sold you a boat. Yep something that makes a hole in the water so you can pour money into it. LOL.

[Bluto]

This post has got me thinking about the new toy I was about to fasten with SS screws into the aluminum boat... talked to a guy at one of the local (non-sponsor) marine supply shops and he turned me on to a product called Tef-gel to coat the screws before screwing them in to prevent galvanic corrosion. Pricey stuff, but now have some on order. The other product he mentioned was Lanocote, but said it didn't last as long as the Tef-gel.

[StrikeFighter]

Thanks for all your suggestions. We as owners aluminum boats need all the advise we can get. As Bill Cosby would say they gave us a pregnant elephant and no delivery manual, who gone to clean up this mess.

<font color="red"> Bluto~ </font> I will check into the Tef-Gel. It sound s like something that I'm looking for.

<font color="red">Boater~</font>you are right give me a good old bead weld look any day over some pansi ansi fiberglass look crevice corrosion nightmare.

<font color="red">Chrome Bumper~</font> I thing you have a good idea there on aluminum.

<font color="red">Backlash~</font>Backlash~Now that something I'm familiar with "backlash". LOL
All of those boat builder are good guys. I guess ever boat builder has the same problem. Prep-Prep-Prep for saltwater use

If people concentrated on the really important things in life, there'd be a shortage of fishing poles. <font color="red"> </font>

[backlash442]

This is really interesting. Makes me afraid to go out and look around my boat.

I think you should post this on the main board. It's very educational.

[aye fsh]

I'd wager a whole bunch of us have reason to be afraid. This sucks. NR has a "finished" seam where the wind shield / Gunnel meet. Not sure about the chalking situation. I have an acquaintance that does soda blasting and industrial painting. I'll have to have a talk with him about how that would work in my situation. Well, here's some photos to freak y'all out with! UGH.


Some of these blisters are around fasteners and such, but some are just out in the wide open all by themselves. If you look carefully you can see a small split in the paint in a couple of the pics










The foam I took out was waterlogged, weighed 50 lbs. The total amount I removed was 8" x 3" x 12' from each side. You can see where it was touching, not touching, and corroding the hull. The top was shaved off on some of it, really opening the stuff up for water penetration.





Here's the part that has me really freaked - These pits are in my hull! Getting at the rest of it is going to be tough as it's enclosed in a box beam. Dangit!






I am so glad I saw this post and checked things out NOW, hopefully I can get this crud arrested and save my baby from the crevice rot!

[backlash442]

Aye Fish, is your boat a North River? Have you had it out in the ocean much? How old is your boat? Thanks.

[Mark Mc]

OMG.....you say that last picture is the inside of the hull??!!

You have a major problem there....like the early stages of an irreversible hull failure. I would be on the phone to the boat builder ASAP.

Sorry for your trouble.....but better to discover it now on dry land.

edit / p.s. - Although this article is about installing aluminum fuel tanks, the concepts here are the same:

http://www.yachtsurvey.com/fueltank.htm

[aye fsh]

Backlash442 - I have a 2000 19' NR W/ 175 Sportjet. I have had it out in the salt and estuary plenty. I have been good about rinsing it and the engines asap afterwards, but not anal about it and going over it with a tootbrush at the top of the ramp or anything. I'm not sure if this problem is exclusive to salt water, I didn't get that impression. From Mark Mc's link:

"Severe corrosion is always caused by water plus a lack of oxygen. Metalurgically, this is known as "crevice corrosion," and the key is to eliminate all the points (crevices) that trap water. As long as the aluminum has a good air flow around all surfaces, contact with water will not damage it."

This being the case, any similarly constructed boats with foam resting against the hull has the seemingly very high potential (if not probability) of corrosion exactly like mine. I have about 415 hours on the main, so I've definitely been out there using the boat since I got it.

Mark Mc - Don't say IRREVERSABLE!! Almost time to get out the JB Weld maybe? Hargh! Ain't that last one a dandy?
It's actually not quite as bad as it looks, yet. It's about 1/16" deep. I figure I've got another 1/6" or two until I'm sunk! (Hehehe, pun intended) I can see how this would just keep on keepin' on if left alone indefinitely.
Thanks for the link. Pretty well spells it out, eh?

Just have to wonder how many boats are out there rotting from within?

[aye fsh]

That's right, Got 'r done! Hey, I've been to Alaska, I learnt how to fix stuff real good!


:grin:

:grin:

:grin:

Before:



After:



Ha Ha! I'm going fishing, I got lots of Duct tape!

[bighugetrout]

Great post! I'm gonna buy a case of Boeshield!

[Flush Release]

Although this article is about installing aluminum fuel tanks, the concepts here are the same:

Movement of air/proper alloy is also a critical componet with alum.

[Ling Sling]

Certain kinds of foam produce a corrosive gas while they cure, especially to Aluminum. Honestly I forget if it affects the spray in or pour foam, but it is a real problem with some of them. Also, I was wondering if there was a product that helped with encouraging the growth of the native oxide layer on Aluminum. I know that we use Peroxide at work to encourage Oxide growth on certain materials. It seems like there must be something that could be applied to an aluminum surface to help grow that oxide layer, but I don't know how that would affect a paint job put over top of it.

[Flush Release]

Generally when you remove the oxide layer by abrasive or chemical it will start to renew itself immediately if no inhibitor is present. Under most circumstances back to normal with 24 hrs.
Most of the problems I see with painted surfaces is generally due to poor prep work or a broken surface that allows moisture to get between the paint and base metal. There are some inhibitors that can be applied as long as it is done before the problem arises.

Alodine is a effective treatment but you have to remember that it is Chromic acid and needs to be flushed with freah clean water throughtly.



As far as foam, always be careful with the stuff. If it can be installed without making contact with the alum. the better it is.

[shimanoman]

HELLO ALL,
IM IN THE U.S.NAVY, MY JOB TITLE IS AIRCRAFT STRUCTURAL MECHANIC, I WORK ON AIRPLAINS.
ONE OF THE BIGGEST STRUGGLES WE HAVE IN THE AIVATION COMMUNITY IS PREVENTING, AND TREATING CORROSION.
REMEMBER, YOU NEED A ANODE, CATHODE AND ELECTROLYTE FOR CORROSION TO FORM.
ONE MAJOR CAUSE OF CORROSION IS DISSIMILAR METALS.
IE-USING STAINLESS FASTNERS ON A ALUMINUM BOAT.
BAD BAD JUJU ESPECIALLY IN THE SALT WATER. BECAUSE IF YOU DO NOT SEAL FATNERS PROPERLY YOU WILL INTRODUCE CORROSION WHEN YOU GO TO SEA.

AND ALSO, MOST OF THE COROSION YOU GUYS ARE TALKING ABOUT IS REFERD TO AS EXFOLIATION COROSSION. BAD BAD STUFF.
ON PAINTED BOATS YOU CAN TAKE A FLASHLIGHT AND HOLD IT PARALLEL WITH YOUR BOAT TO PERFORM A CORROSION INSPECTION.
BUT WHAT YOU NEED TO LOOK FOR IS STUFF IN YOUR PAINT
IE- WORMLOOKING DESIGNS IN PAINT, THIS IS THE BEGINING OF EXFOLIATION, AND BUBBLES IN YOUR PAINT.
EXFOLIATION IS THE WORTS TYPE OF CORROSION BECAUSE 90% OF THE TIME YOU HAVE TO CUT OUT DAMAGED AREAS AND DO INSERTION REPAIRES. NOT A VERY BIG DEAL DEPENDING ON THE AREA, BUT YOU NEED TO DOUBLE THE STRENGTH OF THE REPAIR DO TO REMOVING PART OF THE ORIGINAL STRUCTURE. THIS IS WHAT I DO FOR A LIVING AND WOULD BE MORE THAN HAPPY TO HELP OUT SOMEONE IF THEY HAVE ANY QUESTIONS. <font color="red"> </font> <font color="black"> </font>

[StrikeFighter]

shimanoman Thank for responding to the crevice corrosion post. Its nice to know we have some one we can e-mail when we need advice. You are right the corrosion is a pain to deal with as it really cuts into the fishing time.

PS-If you use all caps in your typing then folks will think you are shouting.

Have a great 2006 fishing season

[StrikeFighter]

Got the boat put back together and after 3rd salmon trip remembered to bring camera to snap a picture of the finish work. I snapped this picture yesterday while on a salmon trip. (see fishing report on I-Fish community for 5/5/05)
It is really nicer to fish on a boat than work on a boat. LOL

[Ricky8fish]

Hi. Can anyone tell me where to get the windshield gaskets pictured in the article above? Thanks.

[lurking_out_loud]

www.geocities.com/alloyed2sea/MetalBoats.doc

Here is an excellent article about corrosion and how it forms in metal boats. This is pretty long, but it is well worth the time to read if you have or are planning to add any gadgets to your boat.

This goes hand in hand with some of the electrical grounding threads as well as the selection of the proper fastener selection for use in our style of boats.

-LOL

[Jedcraft]

Great info: Does the alum. sweating seem to be worse in hotter climates?

[Chesapeake]

Here is a link to get window seals/trim.

http://stanpro.com/Rubber_Two_Piece.asp


I deal with this kind of corrosion alot on older Starcraft boats. The best repair I have found so far is sand blasting, acid washing, epoxy primer, epoxy filler (bondo), then a good top coat.

Sanding and wire brushing wont get to the bottom of the pits without thinning the metal, and they tend to melt and grind debree into the aluminum.

If a structural part is pitted much at all it will need replaced.

If you are going to paint aluminum epoxy is the key.

[SWest Fisherman]

Ouch!!!!!! :frown:

Welcome to the world of painted aluminum boats.

I know that I will get flamed for this, but I am going to be honest here about paint on marine grade aluminum.

Doing a "TOP QUALITY" marine grade paint finish on an aluminum boat is very time consuming and expensive.

Aluminum is a great boat building material. It has many wonderful features that make it almost an ideal material. The one thing it will "NOT" accept is being deprived of oxygen or galvanic action.

A top quality marine paint system cost a H--l of a lot of time and money to do right. Most production boat manufactures can't get the cost for this out of their boats so they have to cut some corners. Top end custom builders that cater to the wealthy buyer can get their price for this type of work.

Even so, paint work requires a lot of maintenance and upkeep if you want it to look nice and protect your investment.

The rule here is to completely seal the surface or leave it completely open to the air. Most paint jobs on aluminum boats are only half way done right when it comes to sealing the surface.

This issue was very rare before aluminum builders starting going "upscale" by offering paint work on their boats. Most corrosion issues back then was from people adding things to the hull without using proper mounting and sealing techniques.

I personally would not own an aluminum boat with a paint job. Boat maintenance is expensive and time consuming. I just don't believe in making a lot more work for myself by inviting crevice corrosion with a paint job.

[Thomas Gilg]

What is the opinion here on salt-water wash, such as: "SALT-AWAY - removes salt, exterior wash and inboard/outboard/jet engine flush"?

--tg

[Caspac]

Originally Posted by Thomas Gilg

What is the opinion here on salt-water wash, such as: "SALT-AWAY - removes salt, exterior wash and inboard/outboard/jet engine flush"?

--tg

I have used Salt-Away on my boat before and after every trip in the salt and I still encountered a crevice corrosion problem. I had to remove the cancer and doing so felt like I was cutting my own flesh. The Dremmel tool, fine grit paper, some new primer and the extra preventative measures hopefully cured the problem. Salt-Away and other products out there work well but they do not eliminate crevice corrosion problems on painted aluminum boats.

[Chrome Bumper]

Originally Posted by shimanoman

HELLO ALL,
IM IN THE U.S.NAVY, MY JOB TITLE IS AIRCRAFT STRUCTURAL MECHANIC, I WORK ON AIRPLAINS..
EXFOLIATION IS THE WORTS TYPE OF CORROSION BECAUSE 90% OF THE TIME YOU HAVE TO CUT OUT DAMAGED AREAS AND DO INSERTION REPAIRES. NOT A VERY BIG DEAL DEPENDING ON THE AREA, BUT YOU NEED TO DOUBLE THE STRENGTH OF THE REPAIR DO TO REMOVING PART OF THE ORIGINAL STRUCTURE. THIS IS WHAT I DO FOR A LIVING AND WOULD BE MORE THAN HAPPY TO HELP OUT SOMEONE IF THEY HAVE ANY QUESTIONS. <font color="red"> </font> <font color="black"> </font>

The USCG and ABS do not requre inserts to be stronger than the original structure in boats and ships. Might be different in airframes, I do ships and boats.
Generally 25% thinning is allowed before insertion is required.

Rust, er, ah, corrosion never sleeps, and it keeps me gainfully employed, so I guess its a good thing.

If painted, ships and boats generally get something similar to:
SP 10 white metal blast,
2 anti corrosive epoxy primer paint coats,
an epoxy binder coat,
polyurethane topcoat.

Use stripe coats on edges and corners.
Paint before attaching hardware.

[Schenley]

I personally would not own an aluminum boat with a paint job. Boat maintenance is expensive and time consuming. I just don't believe in making a lot more work for myself by inviting crevice corrosion with a paint job.

YES!!!!! The salesman looked at me as if I had a third eye when I told him that I didnt want any exterior paint on my Alumaweld Intruder. The above were my reasons as well. I do have some corrosion marking on the hull, but I figure that I will be dead and buried 20 years before it becomes a structural thing!