Why aren't sailing dingies made of aluminium ?

Question

l mean open boats about 12 to 18 feet long, i've never heard of one

Answer 1

aluminum is too lightweight, the CG would be too high for a sailing vessel.

interesting point about the cost -- other kinds of boats, aluminum is significantly less expensive than fiberglass.

Answer 2

because it would cost way more then a fiberglass one.

Answer 3

Besides cost, sailing dinghies get banged around a lot.  Other dinghies, docks, rocks, loading/unloading will all make dents in aluminum but only scratch other materials.