Aluminum
Try:http://www.metalboatsociety.com/Welcome to the Metal Boat SocietyAluminum is a medium seldom used by amateurs but is the material chosen for the construction of top quality professionally built custom yachts, particularly in the larger sizes when investment plays a large part in the decision. It is a material for which it is more important than most that the builder knows what he is doing or the product can be a disaster.Of vital importance is the care which must be taken to ensure that there are no metals more noble than aluminum in electrical contact with the hull, particularly below the waterline. In addition, there are many different aluminum alloys, each with it's own properties and each more or less noble than the next. The correct choice of alloy or combination of alloys must be made or galvanic action will occur between two dissimilar alloys. Welding alloys must also be chosen to be compatible with the two alloys which they are joining.Special aluminum alloys have long since been developed to cope with the corrosive marine atmosphere, with such success that many yachts are left unpainted above the boot stripe. Below waterline they must be painted for anti-fouling reasons but also to form a plastic protective shield to eliminate galvanic action. Mercury based anti-foulings must never be used as they will be cathodic to the aluminum which will be eroded. Copper based anti-foulings should not be used for the same reason except with extreme caution over multiple layers of barrier coat to separate the aluminum from the copper and with routine checking for breakdown of the paint system and consequent galvanic action.The inside surfaces of the hull, particularly below waterline, should also not be left unpainted. A good paint system will give protection from the dangers of lost coins, tools, etc finding their way into the bilge water and setting up a galvanic cell to eat away the hull.Aluminium is much softer than steel so it is more easily formed and can even be worked with woodworking machinery. On the negative side, it must be welded by one or other of the shielded gas welding processes and can, therefore, not be welded out of doors, unless under the protection of an efficient mobile enclosure. Any draft which passes over the weld area during welding will blow away the shielding gas and cause welding problems.Weld area preparation and cleanliness are also very important as even the smallest amount of contamination from sweaty hands or dirty gloves can cause entrapment of impurities in the weld with consequent weld cracking. In general, good welding practice is of far greater importance with aluminum than it is with steel.Aluminum repair facilities are scarce in most parts of the world which are attractive for cruising. Because aluminum is easily cut and drilled by hand, it is better to be prepared for temporary repairs by screwing or bolting aluminum or timber patches over the damage (as for a timber hull) rather than to expect to do a welded repair.The cost per kg of aluminum is far higher than that of steel but the weight of material used in an aluminum boat is far lower than that for the equivalent steel boat. The lighter weight of aluminum allows the use of less and lighter handling equipment and it's easier working, particularly with cutting, fitting and filing, can give labour savings. The net result is that, in the smaller sizes, aluminum construction is considerably more costly than for steel. However, as the size of the boat increases so the percentage difference decreases, with aluminum being little more costly in sizes over about 18m.For the home builder, aluminum is a quiet and odourless material which will produce a minimum of annoyance for neighbours. Grinders must not be used on aluminum and sandblasting is not required so the worst factors against building in steel are missing when working with aluminum.