There is a new boat builder in Stuart selling a couple lightweight tenders 10' and 12' which weight under 500 pounds. https://treasure.craigslist.org/boa/d/stuart-yacht-tender/7239256162.html
Nice rub rail, but I'm not sure how it'd work out as a fishing platform or some of the other uses you could have for a 13' BW. Also it should be pointed out that the 500 lb weight claimed is stripped. The 13 BW starts out at only 695 lbs. with seats, etc. and their 11' only 454 lbs. I think an earlier statement by Soulstice gave the impression that the 13 is a heavy boat, but it's actually lighter than this. They start getting heavier when you add motors, fuel, etc. Pretty much whatever you get in this size range will be about the same weight.
If you're really interested in a flats boat for a tender, check out these guys: https://www.dragonflyboats.net/models/yacht-tenders/ (I know this is my first post, but I have nothing to do with the builder. I just happened to see a 1989 Burger currently listed for sale that has one of these as a tender, and the tender is absolutely beautiful. Whether it's practical or not is a whole different question that I can't answer...)
This is more like what i had in mind. Not sure this is the actual answer but it seems more fishable although maybe not a whaler still. I still think there must be a way to do something out of aluminum that is not a "john boat" think more of a refined fit and finish of some of the aluminum hulls used by some of the rib companies. I enjoy checking out all the ribs at Miami show and I was pretty impressed by highfield. Seem to see them more on sailboats,,, and sailing la vegabonde.
yeah, until the aluminum bangs into your hull while you're lifting or lowering it and scratches the you know what out of paint.