Compression post

Since there had never been a mast stepped - the original builder died before getting that far - there was no hole in the deck, and no mast step. This let me make the decision myself about whether to deck step or keel step. After discussions with the yard staff, including their designer, their looking over the deck construction, and a review of lots of web discussion on the subject, I decided to go for a deck stepped mast. This, of course required the fabrication and installation of a compression post to transfer the deck load down to the floors on the bottom of the boat.

I dusted off my old naval architecture book larnin' from the Acadamy, and calculated what was needed. I looked at the result, scratched my head, and did it again. The result looked FAR too flimsy to the naked eye, so I rechecked a third time, got the same answer, and then asked around. Turned out I was right all along. The strength values for steel are such that all that is actually 'needed' for a compression post is something that just looks completely wrong, and far too small.

I spoke to the fabricator about getting it made up, and he had a piece of 3" square steel tubing just a few inches longer than I needed left over from a previous job. Since he couldn't see a need for a 7' long piece of steel pipe coming up any time soon, he let me have it really cheap. The bottom was welded to a plate cut and sized to span three floors in the bottom of the bilge. Had the boat had a different keel design I might have gone for spanning four, but the floors where the mast goes are sitting directly on the massive oak main keel, so this is fine.

Here you can see also some interesting illustration of the quality of the original work. The copper tubing grounding strap is bolted to about every fourth floor, the whole length of the boat, as well as through the oak main keel to the steel box keel below it. Stray currents are minimal in this boat - even in the very HOT marina I'm in. The pitting in the steel fin keel would have been completely avoided had the previous owner just kept his zincs up!.

 The top was welded to a plate cut to fit between the deck partners, and one side angled down a few degrees to let me rotate the post into place. Here it is screwed to place.

After the foam's put back and the trim and false deckhead replaced, this will look pretty good, and be stronger than needed.