Eastport Pram Build #15: Interior Fillets & Graphite Bottom

After taking a few months off to work on other projects, I decided to dig back into the pram project. The weather is starting to turn nice again and the wind on Green Lake is very inviting. Also, the weekly Duck Dodge races start back up in May! While the boat build had been taken to the point where I could actually go sailing, there were a few issues that I noticed. First, there were water intrusion stains on the interior plywood, which bothered me. When I looked for places where the water could’ve had ingress, the obvious culprit was any seam below the waterline. Even though it had actually only been in the water for a total of about 8 hours, the hydraulic pressure even a few inches below the waterline was enough to push some water in. The months in between were perfect for letting the boat dry out in preparation for additional coats of epoxy.

Sanded, ready for next coat…

I had to wait for a nice day and took her back outside to sand her inside and out, stem to stern. This provided mechanical tooth for the next coat and cleaned up any residue that might be on the surface to interfere with adhesion.

With her right side up, I used my 1″ radius tool to create a large fillet in the seams of all the planks. I had always been bothered by the sharp edges and exposed edges of the plywood. I felt a sense of closure once the seams were all faired. After those cured, the entire interior got another clear coat of epoxy. This gave it that candy-coated look that I was after. Other than some varnish, I consider the interior done.

Smooth fillets on interior seams…

Now I’ve been contemplating the various aspects of this project for over a year now and one of the big questions was the bottom job. I knew that if I painted it, the first little scuff would bother me. I’m also seriously considering storing this in the back of my truck upside down kind of like a camper shell top, so UV resistance is important. After poring over the builders’ blogs and forums, I decided to go with a graphite mix. West System sells a couple of additives like this that can be added to the regular epoxy mix which will provide abrasion resistance and UV protection. I opted for 423, which also gives the epoxy a cool stealthy flat black look. It orange peels badly and sanding is problematic because of the black dust, so I was happy with the less than museum quality finish. Heck, it may even reduce drag by inducing attached turbulence.

Closeup of interior fillet near the aft thwart…

According the to the gurus on the web, 10% mix by volume will give you UV resistance. Up to 50% by volume will actually make the bottom slick. Mixes in between with less powder will result in a harder finish with more resistance to things like rocks and shells. Because I knew the surface area I had to cover, I opted for a double-pump batch, four pumps of resin and two of hardner. As luck would have it, that landed exactly on 150mL in the cup, so it was easy to spoon out 50 mL to get an easily reproducible hard mix. Some folks say to mix it like you do hot cocoa powder where you add the liquid to the powder to avoid lumps. I was afraid that might leave unmixed powder in the corners of the cup. Since I’d been adding wood flour and silica to the resin mixture successfully, I went ahead and did it that way. I did not notice any clumping while mixing vigorously, so started to apply it with a foam roller.

First coat of epoxy on blades…

I started with the blades in case there was some major malfunction at the junction. One thing I did notice is that the mixture is now the consistency of cake batter. Runny, yet viscous enough to resist tipping. When I tried to tip the daggerboard, the epoxy created skid marks under the brush, so I rolled back over it. No harm, no foul. Operating under the philosophy of many thin coats is better than a few thick coats, I rolled it as thin as I could and still consider it covered. It darkened the surface nicely, although I could still see roller marks and wood grain. I knew that a second coat would complete the coverage and make the surface an attractive matte black. NOTE: For the rudder, I didn’t want the part that fits inside the cheek plates to get any thicker and possibly interfere with it pivoting, so I masked off the part that fits inside.

First course of tape acts as a spacer…

Before I mixed up the epoxy, I spent a few minutes masking off the transoms. I noticed on some of the images on the web that the bottom treatment wraps around the edge and goes partially up the forward and aft transom surfaces. This is not an aesthetic decision, this is a great way to add more protection at the intersection and covers both the edge grain of the side panels and stitch & glue holes. The seams were filled with silica thickened epoxy, not wood flour, so the exposed epoxy has a dull, milky appearance that is not very attractive.

Now I just had to figure out a way to do a proper boundary between the bright transoms and the graphite epoxy. I settled on using 1″ masking tape to follow the edge, which I then used as a sacrificial spacer to offset a second course of masking tape. When the first course was removed, I had a perfectly uniform 1″ wrap around. This has the additional benefit of covering up where I sanded through the oak veneer when I trimmed the transoms flush.

Second course of tape butts up against the first course…

First course is removed, exposing a perfect 1″ reveal. Note graphite will soon cover the stitch holes and exposed plywood edges while providing additional protection against water intrusion…

First coat of graphite mix. One more to go, then splash! Maybe this weekend…

The second coat should do the trick. The two panels that were untreated will probably get a coat of Pettit Easypoxy in red to cover the “bad” side of the plywood I used. I coated the blades, not only for aesthetic reasons, but also hoping that the graphite will provide some skid protection, not only on unintentional groundings, but also the normal wear and tear of dropping the daggerboard in and out of the slot repeatedly over the next several years.