aluminum boats

[Levis Minford]

I am looking at a couple of old Strikers (1975-1980) and I am a little concerned about the longevity and durability of aluminum. Are there any issues to look for aside from obvious pitting? Any do's and don'ts?

[cyclops]

The Lowe 16' aluminum fish boat is a "86". It is used all the time for fishing very shallow water. Less the 4'. Not the start of a leak. Original paint and decals with NO care to it. Aluminum lasts longest with no care. Believe it. ALL fresh water only.

[thadJ]

I have Pacific 2001. Love it! If you are dealing w/marine grade aluminum 5056, etc you'll have it 4ever-truly! Check out Black Lab marine's site you'll be sold on aluminum

[Tad]

thad,

Don't believe everything told you by someone selling anything!

Levis,

I don't know if Strikers have sprayed foam insulation inside, but we are seeing lots of problems between it and aluminum. Corrosion, pitting, and actual delaminating of the plate on the inside surface. It looks perfect outside. But the only way to check is perhaps elctronic gauging or remove the foam, a big problem.

Tad

[Thunderhead19]

The Mounties have scrapped about sixteen of their patrol boats because ALCAN produced a large quantity of flawed plate that delaminated. ALCAN had to do a product recall. Is this possibly related?

If the sprayed foam adheres to the surface, it should prevent corrosion. Some companies I know spray a primer inside before the foam to promote adhesion and prevent any moisture that gets in between the foam and the hull from causing rot. Theres a lot to be said for being able to take out the foam easily in case of repairs though. Many people prefer using block.

I can say that I've seen boats with sprayed foam that are fifteen years old and haven't shown any signs of what you're describing, and I've seen severe pitting in boats that are a few years old. Theres something else at work here, and I've been trying to figure it out for two years now.

[Tad]

JD,

The delam problem is definitely (IMO) bad plate. The pitting and corrosion between the plating and foam is, as you say, something different.

There are starting to be lots of conversion or re-configuring of older fish boats here in BC. Of course many see this as easy with aluminum boats, and it should be. Except that most have sprayed foam in the fish hold, which appears to be tightly bonded to the aluminum. Yet we find condensation pooling between foam and plate along the keel. Last summer we re-plated the bottom of a 20+ year old fish boat for about 2' out from centerline because the pitting was almost through the 3/8" plate.

I am now recommending all builders use block foam with vented airspace between hull and floatation. One question is what foam? And can we mold it ourselves?

Tad

[marshmat]

Foam does tend to be a problem with aluminum. Often it will trap a bit of water between the foam and the metal, thus encouraging corrosion. Galvanic corrosion's another issue, easily fixed if you change your anodes when you ought to. Some crappy no-name boats might have less corrosion-resistant alloys, too. "Marine grade" alloys in the 5xxx series are better. http://www.ez.org/aluminum.htm for more on aluminum grades.

As for how the boats hold up- if they're well engineered and built with good alloys, they'll last pretty much forever. It's not uncommon to see a 30- or 40-year-old hull being banged around on cottage rocks and docks, year after year, with no problems. If one of these boats is in good condition, structurally sound and watertight at age 25, it's probably going to stay that way unless you really do dumb things to it.

[Thunderhead19]

I've seen fish-holds that had no foam, and show pitting in the same areas. All I can think of is that fresh water is getting in there and creating an oxygen deprived region. The plate can't passivate and starts to pit. Either that or some kind of debris is getting in there. Carbon from carbon impregnated rubber for example (just tiny fragments) might be creating nucleation sites for corrosion.