If the hull/deck joint is the Irwin style then I really like the 'T' profile rail you've shown, it's going to cover the outer edge and make the whole thing look more finished right off the bat - it also guarantees the aluminum is the outermost piece (not necessarily the case with the top mounted "L" profile rail) making it a better 'rubrail' type of protection.
Using wood you'd definitely want longer pieces. Short bits would not bend as easily and you'd get a 'stop sign' effect at every joint. You really want to minimize the joints in any case to make the varnish more durable (joints are always tougher to keep sealed)
It's starting to look like you want to go with the aluminum - but make sure that if the the mounting holes are predrilled that they match your existing holes (unless there's room to go in between) and, perhaps more importantly, that the holes are inboard far enough to actually get the bolts and washers in without running into the inside hull surfaces.
With a crew you may be able to start the rail at one end (the end with the least curvature) bolt in the first two three, and maybe add some sort of clamp to hold it there for now, and then slowly push the rail into place for the next hole, etc etc, and manage the overall curve that way. However that will required some space alongside initially as the still-straight rail is going to want a lot of room until you form it. It would be interesting to know how the manufacturer's used to do it (nobody I know still adds those rails - cost issues, I imagine, but I think it's a backward step)
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
Last edited by Faster; 02-26-2011 at 12:38 PM.