First time alum boat builder with lots of questions.

Hello, I am in the process of building a 23' aluminum outboard powered boat. All 5086 with some 6061 extrustions. 1/4" bottom and transom, 3/16 sides and decks and .160 pilot house. It has four longitudinals that run from the transom to the collision bulkhead and six transverse frames. two of which are watertight bulkheads. Everything outboard of the longitudinals that are closest to centerline is watertight. I want to cut some holes in the deck and fill these compartments with pourable polyurethane foam. I was wondering if any one knew of a good way to re-seal these holes? I was thinking of gluing down some oversized pieces of plate with 5200, but I think it would look lousy. Any suggestions?

Second, I am going to leave the hull unpainted. there are some areas on the hull that I had to use the grinder on due to mistakes when welding. Is there any way to get these spots back to a finish that will match the mill finish on the rest of the boat, or will it always look bad?

Third, every place that I welded the frames and the decks to the hull plate it is making visible lines on the outside of the hull. Are there any tricks to eliminate or minimize this in the future?

If any one has any suggestions I would greatly appreciate it.
Thank You,
Bob

 

You could use neoprene gaskets under the plates to seal the holes.

TGoz

 

> Is there any way to get these spots back to a finish that will match the
> mill finish on the rest of the boat, or will it always look bad?

Time. In a few years, the surface will develop an even patina. You will still see the areas that were ground, if you look for them, but they will be far less eye-catching.

> Third, every place that I welded the frames and the decks to the hull
> plate it is making visible lines on the outside of the hull. Are there any
> tricks to eliminate or minimize this in the future?

Grind down the raised lines. ( This, of course, brings you back to the previous problem

 

heat lines

I allways just leave them. If you weren't careful and had some burn-through then that's a different matter. Since it is to remain unpainted, any grinding or attempt to buff it out will just make it look worse. If you really want to get rid of those slightly elevated lines on the opposite side of the sheet from the weld then try a power planer set as shallow as possible and make a few passes on them.

 

It is possible to return a brushed finish to aluminum after grinding or to remove scratches or other blemishes. With fine enough abrasive on the final pass, this can approximate the original mill finish. It takes special tools and a fair amount of skill and time. Whether or not it's worth this effort and treasure is purely a matter of preference. I would say "no" but you might say otherwise.

Anyway, here's the tool:

http://www.dynabrade.com/regions/1/ind/midFrameset/proddetail.php?item=13400

I think they will set you back about $1200 for the model most suited to the size of your project, and like any power finishing tool, there is a learning curve. I've got a mini one and with some practice, you can get a real nice straight line mill type finish on any metal.

Jimbo

 

Weld Penetration marks
Not much you can do about the ones that are there but to prevent more look into your shielding gas. If you are using argon talk to your gas supplier about an argon/helium mix. In Aus it was known as 81T and its now called Alushield Heavy. A better gas will allow you to use lower settings resulting in less heat. If this is a problem with the hull it will be much worse on the thinner deck house. Ali welding is different to steel welding. Because ali disipates heat so well you need to weld hotter so you must move faster. The other thing to consider is just tacking the plates together and then paying a qualified welder to weld it out. It costs more and is maybe less satifying than doing it yourself but that would be better than trying to fix buckles and burn through.

Deck cutouts
Weld some backing plate inside the hole in strips and sit an under sized cover on it. You can then weld or glue and fill for a flush finish.

Hope that helps.