Preserving Your Aluminum Boat Hull

Grungy Oxided Aluminum Hull ;  OK, so you purchased a used aluminum boat and it has a grungy oxided aluminum hull.  There can also be salt etched spider tracks on the whole hull that is not painted.  What to do?  You hate to moor it for a week-end in saltwater as that just makes things worse no matter how much you wash it off as this salt creeps out for weeks later.

You have found that a spray can of rust inhibitor like WD-40 helps but only temporarily.  You also find that the boat should have been treated with a product called Shark-Hide before it ever was put in the water.  To late now, but is it really to late?  Can this stuff be applied later?  Read on.

At the recent Portland Sportsman’s Show, I ran into a business that specializes in aluminum restoration for boats, semi-trucks and more.  The business is EZ Way Metal Polishing, a mobile polishing business at   503-709-5579.  The owner, Bob Graham did this on my 18′ North River for $600 plus the price of fuel to my 90 mile distant location for him.

I had purchased this 2005 boat boat used in April of 2009.  It was used for fishing estuaries and lower rivers on the coast of Oregon.  This is also the type of fishing that I do mostly, however I also venture out on Puget Sound or the ocean at Neah Bay or Westport Washington.  It did not take long before I started noticing a salt corrosion starting on the exposed lower aluminum of the hull.  No matter how much I washed it this did not really help.  I finally found if I steel wooled it to remove the worst oxidation, then use a spray can of CRC formula 6-56 Heavy Duty Corrosion Inhibitor that this helped for a few months.

I however hesitated to moor the boat for more than a few days in salt water because of this corrosion.

Bob, his son and nephew showed up at 9:00AM.  They masked off the upper vinyl covered hull, polished this unpainted aluminum with angle head sander/buffers using a 9″ buffing head and 3M Super Duty buffing compound.  They repeated going over the aluminum until they were satisfied it was right.  This took repeated passes, inspection, and go at it again.

The trailer fenders were tried to be removed but the nuts were seized, so they finally just jacked one side of the hull at the rear with a floor jack enough to allow them to access the lower part of the sides.  Then repeat the process for the other side.  The spare tire was removed from the tongue, the front winch stand / bow chock unit was loosened from the trailer and slid forward so they could access the bow.

More polishing until the whole visible sides and under the bow were polished back as far as they could reach.

Once all the polishing was done then the polished metal was washed with new rag saturated with lacquer thinner to remove any polishing residue.  This was then inspected, and if any was not clean, wiped off again.  His criteria is nothing touches the now bare metal until it is coated with SharkHide.

Bob polishing the sides, notice the difference before & after Here the boys are polishing the bow

 Next the painted or vinyl parts was masked off with paper and a coat of SharkHide was wiped on all the metal with a saturated clean cloth.   Let it dry for about 10 minutes.  Then break out the air compressor and spray very light coats of SharkHide.  Light coats so it does not run.  Let it dry 5 minutes and another light coat applied.  Four or five coats were applied before he was satisfied.

The whole process took just over 4 hours for all 3 of them working nonstop.

Spraying SharkHide on sides Spraying SharkHide on the bow

His instructions were to not put the boat in the water for at least 36 hours.  Then after each usage wash the hull off with soapy water and do a final rinse off.  I found on my boat that after a year, I had to lightly steelwool some of the areas that started to have salt corrosion specks, clean and apply another wipe on coat of SharkHide.  This might have been that my hull was rather corroded to start with and that he could not get all of the etching out with his buffing.   Also I found that he forgot to tell me to apply a coating of car wax over the SharkHide as a final protection coat.

He says this coating will protect the bare aluminum for from 3 to 6 years if you take care of it.  He gave me a small amount of SharkHide with the instruction that if I happened to ram a dock hard, it may scuff off some that he had applied.  He said to just use a clean pad, wipe more on to protect that area.

He and the boys made the visible parts of the aluminum pretty, probably even better than when it was new except for some minor etching.

Conclusion ;  There is a difference between corrosion and electrolysis on metals either steel or aluminum when pertaining to a salt water environment.  Corrosion consists of pits, but electrolysis will have a clean bright etching usually close to a dissimilar metal or near the zinc anode.   Either way, prepping is the key before painting or any protective coating.   This can be done with a mild sulfuric acid solution, OR grinding/polishing down to the base metal.  Then for painting, a GOOD primer is needed.  For the above SharkHide the surface after polishing needed to not be contaminated before the SharkHide application.

Bob has been doing this for years and has perfected his technique.  He is meticulous.  He says that if you just wipe the SharkHide on like most salesmen recommend, that yes you will get coverage, but because this product appears to be a lacquer base, any subsequent coatings, if not done lightly will remove or thin the previous coating.  Therefore, his method of spraying the 2nd, 3rd, 4th, even 5th light coat builds up the coats and does not make for a thick/thin streaky finished product.  It took him a while to perfect the spraying method and amount of air pressure required to do the job right.

This SharkHide product comes in two formulas, one is simply  a cleaner, while the other is the preservative.   The cleaner would have been all that was needed if the hull was in a lot better shape instead of the buffing.  This preservative is not cheap, like about $70 a quart.  But one can will do probably 2 boats the size of mine with the quart.

My hull had been exposed enough to salt corrosion, that he could not buff all the slight pitting out.  However my objective was not into this for making it look pretty, but for preservation.

With this being a 2005 boat and been exposed to brackish bay AND open ocean salt, I had really considered painting this part of the hull, but the problem of prepping and then getting it raised up enough to get a good coating under the water line was a problem that I was not really enthusiastic about.  The time involved would have been about the same.  Plus any good primer and paint is expensive.

Here the boat is after & you plainly see the reflections off the trailer on the hull sides

I  was still a bit apprehensive about mooring the boat for any length of time in saltwater as Bob did not do the bottom (other than what was visible from the bow/sides).

I had found before having this done, that a spray on corrosion inhibitor made by CRC with their version 6-56 had done fairly well for a month or so.  So after Bob left and before I put it in the water the next spring, I did jack up one side of the boat from the rear, raising/tipping the hull off the bunks about 3 “,  use 3M Scotchbrite cloth and to take off any salt crystals.  Then I used this CRC product, spraying it on 1/2 of the underside of the hull and let it set jacked off the bunks for a couple of days to dry.  Then move over to the other side and repeat the process.

The following year when I recoated the SharkHide on the sides and bow, that when doing the waxing, I also waxed on the underside of the bottom as much as was exposed, hopefully giving longer protection than the CRC spray on.

This may not have provided total protection, but at least it makes me feel better, plus I got a up close and personal view of the whole bottom.   I even got a chance to file off some rock rash and welding splatter off the keel.

One thing I noticed when doing this is that where the aluminum hull stayed in contact with the older carpeted bunks there was some corrosion on the hull.  This was probably caused by using it in saltwater and the carpet bunk covering became saturated with saltwater, that over time it was the culprit.

I did, the year after I bought the boat purchased EZ Loader plastic/nylon bunk skids that over-lay the carpet.  This was not done with corrosion in mind as I was not aware of it at the time, but to make it easier to offload the boat at a LOW tide where we had to PUSH the boat off the carpet bunks.  It was not an easy chore to offload which the original carpeted bunks, but these nylon pads helped immensely.   Plus now I see the benefit for corrosion control on a aluminum boat.


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