Robin- The compression post as I made the boat had a huge safety factor; at least 400%. The 3/4" bulkhead sits in receivers (bosses) in the liners, top and bottom and is bonded with mat and cloth to both sides to the hull above the floor pan. I'm going by memory here, but I think the mast post itself is made of three teak members, each 13/16 thick. Two are about 2" wide and glued and screwed on each side of the bulkhead, then the third forms the end plate, bridging across the first two with the plywood sandwiched between. By my math this makes a post that is 2 3/8X 2 13/16. Any builder (well, all but one that I know of) would pick thru his stack of teak and use the clear stuff so there would not have to be a reduction factor for knots. Apparently Tom had gaps top and bottom; the top gap would have to have come from dry rot in the balsa, but the bottom gap is a mystery to me in that there is nothing under the floor pan to rot. I'm sure Tom will get to the bottom of it, and he needs to check the bonds of the bulkhead-hull joints if he hasn't already. When we set the floor pan on the 23 we laid out half-sections of cardboard tubes, probably 2", then laid 3 or 4 layers of heavy mat over the whole thing, When we set the pan we weighted it down with sandbags, which compressed the tubes and eliminating any voids. This is common in the industry for the better boats and about as foolproof as it can get, but anything can fail as evidenced by Obama Motors' ignition switch problem. If it weren't for the post being just off center and bearing on the top of the keel (going by memory again, which is always dangerous in my case) he might learn something by banging on the bottom of the hull with a rubber hammer. jerry ----- Original Message ----- From: "Robbin Roddewig" <robbin.roddewig@verizon.net> To: <montgomery_boats@mailman.xmission.com> Sent: Saturday, April 19, 2014 8:54 AM Subject: M_Boats: strength for compression posts
Hi M-list, I am trying to figure out a design for a compression post for my M-23. I have a stainless steel plate being fabricated by emachineshop that will transfer the load from the tabernacle and solid core deck to the three boards that are on the end of my bulkhead in the M-23. I am going to open the floor liner and set the boards on solid hull/keel with a glassed in block of oak at the base. I have some questions. 1.) What is the load from the mast that I need to make sure the compression post will carry? 2.) How to calculate the tensile strength (compression load) limit of the three boards (they will be epoxied together and form a U shape). I am assuming cross sectional area. And I will put in the factor for laminated boards.
Any help would be appreciated!
Thanks Robbin
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