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17. Buttplates

Click on any image to see the full size version

The function of buttplates is to cradle the hips to achieve better control of the kayak as well as attachment for the backrest.

Experimental reduction of the thickness of the core called for extra reinforcement in the form of unidirectional graphite fibers. 4oz. fiberglass is sufficient for 1/4" core.

Note the bright colored patches. These are additional epoxy filler coats for the hatches and in the areas where knees touch the under-deck.
The plates are attached flush to the coaming with a large radius fillet reinforced by multiple layers of fiberglass.

A secondary fillet (gusset) is helpful for reducing bending stresses on the plate as well as lightening the lay-up of the primary fillet .

The photo here shows only the primary fillet. It is strong enough by itself for most uses.

For heavier paddlers or rigorous maneuvers such as rolling, extra reinforcement by a secondary gusset is a good idea.
Backrest attached to buttplates.
Reinforcing the buttpate with carbon cloth not only makes the coaming-plate transition stronger, but it also makes it look more uniform as if the buttplate and the coaming were made from one piece. This task is done during the hull-deck bonding.

This step is very easy to do. Start by applying a masking tape about half way along the coaming as in the picture. Put some plastic under the buttplate to prevent epoxy drippage and epoxy the the patches of carbon cloth right onto the plates. Next day, peel off the masking tape to expose the line where the cloth is fused with the coaming and trim it off. The perimeter of the plate is also trimmed with a knife. Using carbon or plain fiberglass to do this gives the plate a bit more strength. The last step is to sand the transition to make it look seamless. Also, locate the backrest webbing slot and cut the fabric out.
Close-up. It is hard to tell the carbon patch boundary. See the finished coaming .


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