Interesting. I know that the larger yachts and schooners built...

Interesting. I know that the larger yachts and schooners built for specialised uses such as charter and luxury cruises are often built using aluminium. There are (or were) at least two builders inAustralia that do this, namely Australian Aluminium and Steel Yachts in Queensland and Harwood Marine in Yamba, NSW.
One such boat, the 20 metre schooner ' Blizzard' was recently moored in Docklands Victoria and was secifically built for Antartic conditions (it did cruises down there) and had a hull thickness of 2". Scandium would be a boom to these boats as would keel late thickness down and of course, aluminium presents special problems of electrolysis (which can be overcome).

Smaller sea craft such as tenders and Buffalo boats are also in aluminium which is exepnsive to weld.

Ease of welding would also increase the range of uses in fixing fittings that currently can only be riveted onto aluminium using stainless steel to avoid electrolysis.