Bowmar cast aluminum hatch refurbishing

I pulled the two approximately 20 inch x 20 inch cast aluminum hatches off my 1977 Allied Seawind project the other week because they leaked and finishes were in poor shape.

I sandblasted them in the cabinet blaster and they now look great. I have lots of 1/2 and 3/8 acrylic around the shop to replace the lenses.

Now my only question is how should I refinish the frames or should I just leave them natural.

They were originally painted black then top coated white. I hate to refinish them with a product that will just fly off in a few years. On the other hand if I leave them natural will the cause and issue with black staining on the deck all the time?

Looking for all opinions and suggestions.

Sadly, aluminum left unpainted forms aluminum oxide (which is the coating that keeps it from corroding) which some find unsightly. It is dull and not always uniform. If you paint it it will only last until a small amount of moisture gets under the coating then you get that white powder forming and the aluminum disintegrates and the rest of the coating fails. Anodizing will protect it longer than paint but it is easily sun-damaged, then it fails and see above. Another complication is the poor alloy that many manufacturers use. My boat is entirely grey and is made of a marine alloy but places where the plates overlap or in one case down below where the foam coating failed and some moisture got in, a (fortunately) non-structural 1/4” plate just disintegrated and vanished.

If you get that corrosion you have to cut it out completely as it gets in the “grain” of the metal and just keeps going.

Paint works for a while but you will have to regularly remove it and repaint. I’d leave it grey but you will be disappointed. You could replace them with stainless but they will cost you at least a boat dollar each.

No deck staining with natural aluminum. I don’t get those black streaks that plague fiberglass boats.

I think that keeping paint on them will be difficult. Maybe powder coating but again there will be a tiny bit of corrosion left somewhere that will start the coating coming off. Maybe look at Shark Hide coating. It is for aluminum and supposedly keeps it shiny. I have not tried it but it looks promising. You have to reapply it every now and then but it is pretty much wipe on and wipe off.

I was an airframe mechanic in the Navy & worked on a lot of aluminum surfaces. After sand blasting we coated the part with apple cider vinegar & let it dry. This tended to slightly etch the aluminum which held the paint better. Then a spray coat of zinc chromate and lastly a paint and color of your choice. Now days I use Rustoleum as my final coat and it holds up great!

Xsbank said:

Anodizing will protect it longer than paint but it is easily sun-damaged, then it fails and see above.

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The anodizing is unaffected by the sun, but the dyes used to color the anodizing can be. If you have them hard anodized (ask for Mil Spec MIL-A-8625 Type III Clear with D.I. seal) it will be a dark brown almost black, with no dye used and will last a long time. Ornamental anodize like on lawn chairs is maybe 0.0005" thick and fairly soft. True hard anodize is about 0.002 thick and about half as hard as diamonds - much harder than steel or even tungsten carbide. it will outlast any other coating you can put on it. It cannot be scratched by ordinary things and is very resistant to chloride corrosion.

I have those same hatches. They are great. I just rebuilt them, myself.

Catalina Direct has the lenses in stock. Turns out they were used in many Catalina sail boats.if you don't want to make your own, I can vouch for theirs fitting like a glove. I bed them in Dynaflex 230.

As for painting, sand to clean them up then prime with an automotive self-etching primer from any auto parts store or Rustoleum's aluminum primer from Home Depot or Lowe's. I bet a zinc chromate or phosphate primer would be a good 3rd choice, but never tried. Then paint as usual.

Thanks everyone!

I also have those hatches and love them. Just as an FYI Defender has some parts for them if you need them.

Ken