Fitting the deckbeams part 1


Deck Beam position
If you are working from plans or are working from a book/CD, the deck beam positions will either be given or else you are shown how to determine where they should go. It comes down to fitting the lower body into the structure at the correct point with relation to the centre of buoyancy of the craft and marking off the beams either side of that.
Specifically there will need to be one that supports the rear of the cockpit, and one not far behind to take the weight of the paddler sitting on the rear deck. In front there will be a beam that also acts as a thigh grip if a small cockpit is fitted; it helps to know the paddler's dimensions to determine the position. In front of that there will be more raised beams and then one which will act as a footrest or to take the front of a foot-peg fitting. Other beams are fitted towards each end of the boat as needed.
On this craft which originated in the "Freeship" computer program I added the positions according to the principles described above around the calculated centre of buoyancy using the "intersections" command.
Securing the deck beams
Two ways are commonly used to secure the deck beams to the gunwales; they can be held in place with dowels or they can slot right through the gunwales in a mortise (the slot) with a tenon (which goes through the slot) to form the joint of that name. Using dowels is easier and quicker but generally reckoned to result in a slightly weaker structure. The latter method is also much more satisfying and is described below.
Cutting the mortises

Beneath the cutting tool is a wedge of 13 degrees which is the angle that the gunwales are planned to set, off of the vertical. This results in quite a gentle sheer. 
The photograph is not quite accurate as I was holding the camera with the other hand which would normally be pressing down hard on the top edge of the gunwale to prevent it riding up and jamming the cutter when you let it rise after the cut.

The picture of cut mortises shows the vertical markings of their position, but not the horizontal which were marked with a mortise gauge. My quarter inch slots are 1 1/8" across and about 1cm below the gunwale top. The width of the slots is dependent on that of the deck beam stock. In the next post I will describe how the tenons are cut.





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