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got the beams uncovered from their cellophane (hep me lord!) from the guy i got the tiki 21 from. As expected, one beam of the 3 rotted away. What looks to be the fore beam. This is the boat that i have no plans for, and while i have a few drawings, have no specs. BUT my plan is to replace this beam which is an H style, or joist I beam style, however it is called. To replace it i think to use a box beam to the same dimensions made of marine grade plywood, triangular section shape or more like trapzoid in section, with glass and expoxy resin.


Also i have only 3 beams. So looks like i need to make one for the stern.  Again, will likely build as box beam style with floatation foam inside.

The thing about box beams of any sort is to engineer against the expected torque. So in this case i will place internal, blocking, baffles that will prevent any twisting, also of 3/4 inch marine ply. Then with the two part pour in foam, it will likely not shift about. Further reinforcement from the external layers of glass and resin will finish it off.



Any cautions of which i should be aware?


also pretty ignorant pig about the tiki 21. This one undoubtedly has a strange history as it is built of some of the best mahogany ply i have ever seen, with an incredible resin job, only it is polyester, not epoxy.  Sooo a bit older than i was told. Also this boat has been launched, in spite of what he was told (the guy i got it from). And the deck is some of the best surface work i have seen (painting i mean), but so far half the glass cloth we rip off did not wet out properly. So no wonder the rot. At least in the deck. The rot in the beams was the fault of the guy who wrapped the thing up in cling film like it was a brisket.


anyway, with help of crew and assistance of universe, will be out sailing it by end of july. 


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IMHO, adding foam the the interior of the beam is not a good idea.  It will add negligible strength and will tend to trap moisture.  Think of it as putting the cling wrap on the inside of the beam.


In order to add torsional strength to the beam, the foam will have to resist both tension and compression, something foam is not known to do.

Ah, good points. Makes sense....will leave that part out. Also foam is messy. Planning to glass and resin coat the new beams.  Have one beam rotted through, one that is a bit too springy for me when i walk on it, so will replace all. Plus am engineering a carbon fiber clamping mast tabernacle to bind my unstayed mast to the beam, and it will be easier to work off the planar surfaces of a trapazoidal box beam.

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