Indeed. I do like the multiple I-Beam composite, great graphic. It's an engineering challenge! EG how thick do you make the webs? The more you think about it the more feasible it becomes.
The verticle supports inside, two placed about where the original doorway is, should do it. Could also buildup wide pads on the beam to spread the 'point load' of the supports.
Mike Goodwin introduced us to maranti "Aquaply" and "Hydroply" which are superior in every way to American fir - that stuff would make a good arch - ala Frank's post. Thanks, buddy! 3/8" of maranti equals 3/4" american fir. I would not use FinnPly. Would caution that cutting the 2" wide curved pieces out and gluing those together side to side to get your width is not such a good idea. There still will be flex don't you think? Could you put it on the floor and jump on it??? Even with the extra wide width I think there is not enuf 'meat' in 2 inches. Would like to debate this. I'd be happier with 2 1/2". Plus the two columns inside. As you know it's imco. Frank, though, of course meant bending 1/4" over a form and gluing up a 2, er, 2 1/2" stack! Only with meranti.
A composit structure composed of two skins separated by foam, endgrain balsa, honeycomb -essentially a nonstructural filler - will be stiffer than a solid lay up. Also lighter of course. But we can't forget that the load on the beam is concentrated in one place. Spreading out that point load is very important. Correct?
What we learned about an unrestored Ariel with a flattened cabin-crown under the mast is that the original Pearson structure (beam, strut braces and bulkhead) while funky was still working and in good shape. (On 338 anyway.) The structure had probably 'settled' or shrunk over the decades allowing the rigging to pull down on the mast. That is, it was more of a result of aging materials rather than the weight of the mast, or rot. After the two screws that hold the round wood maststep to the beam inside were removed, the composite cabin top popped back up to it's original crown!! Or pretty close to it - how about that?? That's the challenge confronting the renovator. We need to make some structure that will not move over time. This time. Or one that can be adjusted up when needed. I'll take the immovable, with some redundancy built in. And everything GLUED IN. We live in the age of incredible glue.
If one had the time, testing various structural ideas would be revealing. We'd need the various arcs and a carjack and some sort of meter. But doing this in the imagination is a good alternative. One can 'see' the various ideas and how they might be expected to react to a carjack (or an unmetered jumping attack by a twohundredfifty pounder wearing Redwings!) trying to straighten them out.
I'm oldfashioned and think solid heavy oak will do. But a well thought out composit of carbon fiber and the best epoxy would be much lighter and more in keeping with the technologic advances of this era.........Would be a curious jig to come up with! Vacuum bagging, anyone?
The load on the compression beam is constant - and no doubt there'll be times when sailing that the load exceeds the norm, would be constant AND 'pumping.'
Gotta go to work
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(Supposed to be working...) How about bent square (rectangular) steel tube? Easy to get the arc done. Get the best curve, weld four of them togther side to side. Fill the odd angles and spaces up top with epoxy mix using the beam with a film release. Take it down. Then glue it back up with rubber. No?
Might get a clear span out of that one. And however the supports go, they also could be the same tube all welded together. There's that old problem of what the finish will be: chromium oxide? Wait a dang minit... Use the best quatity iron (the other steel) tube and get it galvanized. No stinkun chromium oxide and no sticky epoxy!!!
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