Materials to use for boat construction?

[cheddar]

Im looking for a good material to use for walls that is light weight and some what inexspensive.

I was thinking of cutting galvanized sheet metal in 2 foot sections with two 90 degree bends in each end. I could rivet or screw each panel together after i stuff it with foam for insulation. The bends when fastend would be my support. The wall would become one when a inside layer was attatched.

What do you guys think?

I know alum would be the best but i was thinking of costs.

[gonzo]

What kind of walls? If they are partitions, plywood is the cheapest and easiest material to use.

[cheddar]

they would be used on a pontoon platform for use as cabin walls. They would be exposed to salt water spray.

[abohamza]

What is the pontoon platform material?

[gonzo]

Sheet metal would be rather heavy. You can use 3/8" siding plywood. It is textured and can have vertical grooves. Frame it with 1X3 for light weight.

[cheddar]

Deck material is plywood over alum frame.

Ref to 3/8 siding plywood. Do you me T111?

[alan white]

No way should you be using steel sheet metal for exposure to salt water.
Plywood is the best choice. It's light and strong, and it won't mind a bit of salt water. Use a good exterior plywood (AA or AB or AC exterior rated). 3/8" is fine, with outer grain running at right angles (!) to the framing (maybe 1 x 3 studs 12" on center).
If you fiberglass tape the seams it will last longer, but a good polyurethane builder's caulk can be used to fill the joints as the panels are assembled. Stainless nails are good for attaching plywood. Then paint on two or three coats of deck enamel.
T-111 is sold in varying thicknesses, and it does look finished, if rustic. I personally don't recomment it because it's weak compared to regular plywood, or another way of putting it is it's heavy for it's strength because of the grooves. However, you may like the look. if you use it, maybe you could run it horizontally over vertical frames. The other way, the walls could become wavy over time.
You can also cover plywood with the thin panels sold in box stores for use on commercial kitchen walls. Pebbly surface, fiberglass or Kydex, available in white or off white.
Totally washable and long-lasting in tough conditions, but cost may be a problem.

[cheddar]

Thanks Alan White for your help. I needed direction.

[Ad Hoc]

Plastic sheets say melamine...if your only criteria is weight and cost!

[rwatson]

A lot of plastic sheet, melamime especially - is not particularly UV resistant as I recall, and I dont think its particularly cheap either.

If you didnt like plywood for some reason, you can layup fibreglass on a flat smooth table, (melamine is good for that table surface ) with a layer of gellcoat then chopped fg mat, then fg cloth, and make some great looking panels. The table contact side will be smooth and prefinished when cured.

The advantage in making your own fg panels on site is that you can make them bigger than the standard 8' x 4', and have less joins. You can also make shapes that can 'fold' themselves to a non straight edged shape - like a curved windshield.

[alan white]

MDO plywood is another excellent choice for walls. It stands for medium density overlay. It means a plywood with a surface resmbling Masoniite. Very paintable (it's what sign painters often use).
Then run it horizontally and cover the joints (one will be halfway up the wall) with a 1/2" half-round molding. Then paint. Inexpensive, sailorly looking, and long-lasting.