Thursday, July 21, 2011

Aft Forward Deck Beam

Just the sound of this particular part of the boat sounds crucial to me. The Forward Deck or Fore Deck is the upper area of the boat in front of the cabin. The aft forward deck beam is the most rearward of the forward deck beams. It ties the the forward part of the cabin into the deck and supports many of the other deck beams.
At this point anyway I think of the aft forward deck beam installation as heralding the final phase of  the building of SKORPA.


The AFDB is constructed of plywood and Doug Fir. The plans have a full size pattern for the plywood, but since I have extended my cabin forward 6 inches the AFDB had to move forward as well. Since SKORPA is not at all shaped like a box the beam had to be altered to fit its new location.

This step involves gluing solid stock 1/2 by 3/4 inch to the plywood to make a composite beam If you look carefully you can see that I used scraps of wood to form cantilevers so I could develop clamping pressure near the center of the table.

Next the beam is installed in the boat just at the front edge of the cabin which is suspended by a rope to the ceiling. Actually you can not see the rope holding up the cabin but you can see two other ropes. One is holding the AFDB up in place while the epoxy sets and the other is applying a little pressure inward on the gunwales.








The Aft Forward Deck Beam is in place and the forward part of the cabin settles nicely on her and becomes part of the boat.


The center forward deck beam uses plywood only for the knee part that transfers the load over to the hull. The span is constructed of five pieces of cedar laminated with epoxy. I mad a mistake with my measuring and built the first CFDB without enough camber. I considered soaking it and trying to put more bend into it or adding some spacers but in the end I decided to build a second one. Consequently I have lots of photos.

Each strip is coated with a low viscosity epoxy.


Then thickened epoxy is spread on one surface using a notched trowel.
Then the pieces are stacked one on top of the other. As you can imagine this can get messy. Thickened epoxy has some of the properties of grease.



My form consists of a series of block clamped in place on the plastic covered table. The position of these blocks determines the camber of the beam.



Clamps are added to squeeze the layers together and to keep them all pressed flat against the table.




There is a delicate balance. You should have enough epoxy evenly spread on the parts. The pieces need to be held flat to the proper shape and squeezed together hard enough to get some squeeze out but not so hard that most of the epoxy is squeezed out and you have a starved joint.

There is normally some spring back when the beam is removed from the form. The narrower the strips and the more flexible the wood the less spring back occurs My beam straightened out less than 1/8 inch..