Finishing the Bilge Pump Supports

The inboard support was scraped, chop strand mat was squished between the frame and the bulkhead, and the support was screwed into place. Now it is time to do the outboard support.

The outboard support is has a vertical batten running right next to the frame. Scraping the paint off the inside proved challenging! I have been using a regular block plane for the paint scraping, but the blade doesn't reach the edge. I have a rabbet plane, but I elected not to use it because the paint makes a mess of the plane. My block plane is covered with a white mess of dust from the paint and wood after just a few scrapes. The rabbet plane has a lot more nooks for that dust to get into and cleaning it all out would be a nightmare!

Instead, I chose to go a simpler way and use a regular 1/2" chisel. With a sharp edge, the chisel was able to get under the paint and lift it off the wood without taking too much wood with it. The chisel is not as precise as the planer, and it did dig into the wood from time to time. Luckily, any damage is superficial and about to be covered by fiberglass and resin.

With the sides scraped, I stuffed the ends of the frames with chop strand mat to help hold more resin and aid in the bonding process that will follow. The gap that was created between the outboard frame and the vertical batten was filled with chop strand mat. If I did not fill this void with CSM, water and dirt could accumulate here and it would be harder to keep clean. It would also drastically reduce the bonding surface area which in turn would reduce the bond strength of the frame. By filling the void with CSM, resin will be held in place and this void will become a solid block of plastic that will bond the frame to the batten, as well as the rest of the bulkhead. This will provide a very strong bond that will be able to support the forces and stresses that will be placed upon it when we begin pumping 1 gallon per stroke!

The pump was test fitted multiple times to make sure that the bolt holes still line up with the frames holes. If I were to screw the brass angle brackets into the wrong hole, the measurements between the bolt holes would be off and would not line up with the bilge pump. Each time I removed and installed a frame, I would test fit the pump to make sure I was in the correct hole. 

Now that all the frames are in position with chop strand mat squished in the void between the frame and the bulkhead, and the pump has been reinstalled for a test fit, it is time to finish up the minor details. The brass angle brackets came with brass screws for installation. These brass screws have served their purpose as a cheap, temporary fastener. Repeated installation and removal can wear the heads of the phillips screws, so using the free screws removes any worry about wearing the heads during the fabrication process. With everything finished, I switched the screws from brass to stainless steel.

These small stainless steel screws will serve as a direct replacement to the brass screws, and since they will only be installed once, they will have fresh heads and no chance of stripping or wearing. Stainless steel is really strong when using small screws like these, but they can suffer from crevice corrosion when encapsulated within the fiberglass layup that will follow. This is ok, as the screws are only needed for initial support of the frames. The real strength comes from the bonding that will follow. While the screws will not offer much strength, stainless steel screws are still better than brass screws in boat construction. The ideal metal for marine fasteners would be bronze, as it is strong and does not suffer from crevice corrosion. The problem with bronze is it is not as strong as stainless steel, so the fasteners need to be larger for equivalent strength.

It all comes down to compromise, tiny and strong but corrodes (stainless steel) or large and strong (bronze). Since these are only required for initial stability, stainless fasteners will suffice. If the frames were to rely on the screws for final stability, they would need to be up-sized and bronze would be the ideal material.

Up next, we will bond the frames to the bulkhead using fillets and tabbing for a full fiberglass job.