Robbin, I had a civil engineer run some numbers for me on just that issue. What IS the compression load likely on, in my case with an M17, a sailboat with about 200 sq feet of sail up in, say, 25 knots of wind. It came out to about 1000 pounds. I also found out that a 4x4, yellow pine, #1 grade post, eight feet long with no side bracing will handle the compression load of about 6000 pounds. So a shorter post and one with side bracing such as a bulkhead will handle considerably more. Then too if you choose oak, the numbers would go even higher. Fair winds, Tom B On Sat, Apr 19, 2014 at 10:54 AM, Robbin Roddewig < robbin.roddewig@verizon.net> wrote:

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

Thanks for all the replies! I have some differences with what was described as standard and I cannot of course vouch for what other owners have done to alter the boat as delivered. My bulkhead is only tabbed to the port hull and is sitting on the liner. It is a half bulkhead only on the port half. It has a ridge in the floor or ceiling in front of the bulkhead but nothing on the stern side top or bottom. It is not tabbed to the floor liner. I can move it fore and aft by pushing on it. It is not tabbed to the ceiling either and does not touch the ceiling. It has about a 1/4" gap. So any load from the deck/ceiling is only transferred through the trim pieces screwed to the bulkhead. Which is not what I would have expected. I will probably tab it to the ceiling for the heck of it and to the floor liner as well. My three boards which Jerry describes very accurately were screwed to the bulkhead and each other. I plan on gluing the three boards together to make a U shaped post and attach them to the bulkhead again. The floor pan is not on the hull. And I can reach under the head and feel a gap between the pan and the hull. The three boards have cracked the floor from the mast load which ceased to be spread by the rotted core in the cabin top and let the tabernacle push directly on the boards. They cracked the floor and made a depression but are still not pushing on the keel. I plan on opening a hole in the floor and building up a square out of epoxy soaked oak or G-10 to set the bottom of the teak "post" on. This will make a direct load path to the keel that is helped by the bulkhead. I think the original design had a lot of margin but I find it easier to overbuild the repair and make sure the three board post has a clear load path to the hull/keel and that the bulkhead is taking loads from the deck and transferring them over the liner pan as well as the port hull. Thanks for all the help!! Robbin On 4/19/2014 3:50 PM, jerry montgomery wrote:

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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Larry, I get mine at a rural airfield near where I sail.  I put3 3 gal tanks in the truck and drive up to fuel pump.  The attendant comes out and fills them up. I don't know how big the airports have to get before this is not possible but you might call the general aviation airports near you to find out. Thanks Doug On Monday, April 21, 2014 11:09 AM, "Hughston, Larry@DGS" <Larry.Hughston@dgs.ca.gov> wrote: How do I legally get "Unobtainium" NON-Ethanol fuel at an airport?    ---Larry (still looking) -----Original Message----- From: montgomery_boats-bounces@mailman.xmission.com [mailto:montgomery_boats-bounces@mailman.xmission.com] On Behalf Of bownez@juno.com Sent: Wednesday, April 16, 2014 8:04 PM To: montgomery_boats@mailman.xmission.com Subject: Re: M_Boats: Deck repair Hi Larry, Dave Scobie's advice is right on. He beat me to an answer. Doug's suggestion for aviation fuel is good too, it will really make your C-Dory fly! I have the advantage of having a gas station a half mile from me that sells non-ox fuel. I feed it to the motorbikes and the outboards.Pricey, but worth the piece of mind. Later, Bones ____________________________________________________________ Old School Yearbook Pics View Class Yearbooks Online Free. Search by School & Year. Look Now! http://thirdpartyoffers.juno.com/TGL3141/534f44d4921b944d416edst03vuc