MATERIAL
GRADE SELECTION

Aluminum is distinguished by alloy series. Only two are of concern to the home builder. They are the copper free marine alloys of the 5000 and 6000 series.

The differences between the 5xxx and 6xxx series are the alloys contained in each. The 5xxx series is a magnesium based alloy while the 6xxx series contains magnesium and silicon.

The latter xxx denotes alloy proportions. There is also an Hxx value. It indicates the temper of the alloy. By changing the alloy proportions and temper (Hxx values) the stiffness, malleability, and weld ability of the material can be varied.

These marine alloys have numerous variations, but there are only a few variations that we need to be aware of in the construction of yachts or small sailing craft.

The 5xxx series has more malleability and is less stiff than the 6xxx series making it easier to form to different shapes.

Make the 5xxx series your alloy of choice, using the 6xxx series only when structural shapes, extrusions, and piping are unobtainable in the 5xxx series. Both the 5xxx and 6xxx series have very good weldability, and can be welded using both the MIG and TIG welding techniques.

There are two designations within the 5xxx series which are most suitable for yachts and small sailing craft constructed by the homebuilder. They are 5052-H32 and 5086-H32. Of these two alloy designations 5052-H32 is the easier to work with. It is less corrosion resistant and has less strength than 5086-H32. In small sailing craft the corrosive resistance and ultimate strength between 5052-H32 and 5086-H32 are not considered a problem.

If you are using 5052-H32 for plating the hull will need to be painted. Painting is the norm for estechtic reasons when constructing yachts and small sailing craft and obviates the corrosion resistance factor between the grades.

On the other hand 5086-H32 is the better grade to use. While it is harder to work than 5052-H32 it is more corrosion resistant and ultimately stronger and is of course more expensive.

Most builder of aluminum boats are in the "Know". They have read about aluminum material designations. Using 5052-H32 for the shell plating may be acceptable, but considered a poor choice by builders using 5086-H32. To have your hull looked upon favorably use 5086-H32 for the hull plating.