Anthony,

The Welsford "Roof Rack" would be very easy to build in aluminum. If I were you, I'd find a local fabricator who works in aluminum (probably builds tanks etc) Ask him whats the thinest stock he can easily weld. That should be around 2 to 3mm. For this case 2mm would be better but 3mm will work very well as well.

Then propose to your fabricator that he orders the material (5000 series material he will most likely be able to get it cheaper than you can and his small profit on the material will sweeten him up as well) and welds up the dinghy for you. You cut out the panels (just needs a good jigsaw and the correct blade) and then using the same technique that you'd use for stitch and glue construction, you drill some holes close to the edge (3 - 4 mm) and then pull the shape together wiring as you go. You want to use as few wires as possible as the holes will need to be welded close. When you are done, the whole structure will be quite stiff and you can then take it to the fabricator and have him weld it up for you.

You may need to stiffen the bottom a little. Three or so stringers from aluminum angle (about 30x30x2 or 3mm, placed so the open side of the triangle is against the plate) will do the trick. The stringers should not be fully welded, just staggered long tacks (about 25-35mm). leave the ends open. The stingers can be inside or outside. I'd put them outside as it would make cleaning the inside easier and will give the bottom a bit of protection.

For the gunal (spelling?) 25mm tubing can be tacked on. The above should give you a light and near indestructable dinghy at a very reasonable price. No need to paint.

David Tyler wrote:Zuleika Louise carries very heavy ground tackle, doesn't she? I'm certain that if I tried to lay a 35lb anchor and 30m of chain using a very small dinghy, I'd drown myself. My kedge is 22lb with 5m of 8mm chain, and that's all I care to manage in a 9ft hard dinghy if it's choppy (and it's likely to be, if you need the kedge). An inflatable is more stable, and has more buoyancy.
A hard dinghy is harder to get over the rail than an inflatable. It's taken two of us up to now,  on Tystie, and as another elderly gent, now single-handing, I'm going to have to invent a system for doing it without knocking paint off the tender and Tystie. Thanks to my davits, though, I only need to get the dinghy on deck for long offshore passages.

ZL is herself a heavy little number, with all that iroko, and I am entirely happy with her ground tackle.  In fact, the Bruce is intended for quick deployment in preventing myself from getting into embarrassing situations .  Having got into said situations, for hauling myself off I have an elderly Hall-type anchor of about 20lb, with 5m of chain and 50m of rope, which normally serves as the stern anchor.  

Zuleika Louise carries very heavy ground tackle, doesn't she? I'm certain that if I tried to lay a 35lb anchor and 30m of chain using a very small dinghy, I'd drown myself. My kedge is 22lb with 5m of 8mm chain, and that's all I care to manage in a 9ft hard dinghy if it's choppy (and it's likely to be, if you need the kedge). An inflatable is more stable, and has more buoyancy.
A hard dinghy is harder to get over the rail than an inflatable. It's taken two of us up to now,  on Tystie, and as another elderly gent, now single-handing, I'm going to have to invent a system for doing it without knocking paint off the tender and Tystie. Thanks to my davits, though, I only need to get the dinghy on deck for long offshore passages.