Ballast Tank Inlets

I have begun sanding the epoxy coating. First with coarse (80 grit) paper on the flat areas to remove the tops of the hills, bubbles caused by air coming out of the timber, dead insects, etc. Miraculously I didn't have any major runs to deal with. After the 80 grit I will change to 120 grit and go over the corners carefully so as not to remove all the epoxy. Then another pass over the whole hull with 120 grit.

While sanding the garboard plank (next to the keel) I sanded around the inlet to the water ballast tank and thought it might be worth a couple of photos. First  an explanation: the Able has two water ballast tanks in the bottom of the boat on either side of the centreboard case. Each tank holds about 45 litres of water providing about 90 Kg of ballast. The tanks are filled after the boat is launched through two holes in thebottom of the hull. As the water enters the air is pushed out through a vent pipe inside the hull. When the tanks are full the vent is closed so the water cannot run out of the tanks. When the boat is taken from the water on its trailer the vent is opened and the water runs out through the inlet holes. If the water ballast is not neededm boat already heavily loaded with crew and/or camping gear, the kept is kept closed preventing the water flowing in. Well that's the theory, I hope it works out!

Here is a photo from outside the boat. The result of the coarse sanding can be seen around the hole; the shiny areas are untouched.

 

The hole in the plywood plank is 32 mm daimeter with a small chamfer around the edge. The white tube is a plastic plumbing fitting with a 25 mm hole through it. To improve the glue bond to the plastic I put the fitting in my metal turning lathe and cut a shallow fine pitch screw thread on the outside. Then, after painting the edges of the ply around the hole with unthicked epoxy, the tube was screwed into the hole with plenty of thickened epoxy around it. After the epoxy set the tube was trimmed flush. The tube will protect and seal the edge grain of the hole in the ply.

 

On the inside of the hull, photo below, things are not so tidy! The back of the tube butts up against the inner part of the keel and the spaces either side of it will be filled with thicked epoxy to provide more support for the tube. The front of the tube will be cut away flush with the inside of the plank so that all the water can drain out. This will be done after the boat is turned over.