Posted by Mike Turner Link: Fiddlestix for Sale - Reduced Price
on 11/3/2009, 5:33:51, in reply to "Removing compression post"
The compression post doesn't just keep the cabin top from sagging, it also carries the compression load of the mast down to the keel.
My boat (Rob Roy 23) uses an arched teak beam instead of a compression post, but the beam doesn't take the load over to the gunnels. Instead, it takes the load to two compression posts, which form a door through the bulkhead beteen the salon and forepeak, which in turn rest on a "floor" of wood that spans the cabin under the sole, and rests on the keel. So the compression force is still on the keel.
The compression force can be substantial, even on a small boat, when the rigging is set up. I found this out when I tried to remove a screwed-down section of the cabin sole to remove my marine toilet for repair - couldn't figure out why I couldn't move the piece of sole after I'd removed the screws, until I realized that one of the compression posts was partly resting on it (the post was notched to accept the sole, and continued on down to the floor resting on the keel).
Chainplates are the same way - when properly installed, they attach to bulkheads or other means of transferring the forces and loads of the rig, to the keel.
Small boats may not have that much load - but it's probably more than we realize, including shock loads of improperly tuned rigs.
Whatever method you adopt, also periodically check the compression post, beam, etc. to ensure its integrity. Any water intrusion in a wood post can lead to rot, and trouble. On my old Catalina 30, which used a wood compression post, the head's shower drained to the bilge, right past the base of the post. The water allowed rot over time; the rot allowed the post to sag; and the sag resulted in a dishing of the cabin top on the deck beneath the mast. This was such a common problem that Catalina had info on its website about the options to fix it, and even sold a replacement base for the post.
Mike Turner
Rob Roy 23 yawl "Fiddlestix"
Mobile Bay, Alabama
101
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