Photos taken by Jim Franchi, April 9, 2011, of the rebuild of the mast step. These show the construction detail quite well, and especially the member called the “carlin”.
The carlin is a fore-aft deck member, here the slightly reddish phillipine mahogany board. Shannon is fitting the carlin.
A good view of shannon's frame, the trapezoidal piece installed just in front of his knees. The two vertical boards just touching the frame will be the sides of the mast step. A hole called the “partner” must be cut into the carlin to accommodate the mast. Also the two short verticals (installed a couple of years ago) are the cleats that hold the base of the sampson post. A second hole in the carlin will accommodate that post.
Showing how the stem is mortised into the front of the carlin, and the carlin into the frame. The latter mortise is particularly important, as the carlin absorbs the side thrust from the mast and transmits that to the frame. That thrust can be a thousand pound or more. The frame wood and other lighter new wood is white oak.