Building Logs

Port Dagger case glassed in

Posted by Paul

During the week I glued and glassed the ply outboard pads onto the rear bulkhead. The bulkheads already have way oversize back filled holes that will meet up with the holes on the tracks. I wont attach the tracks until I have made the trucks, which comprise aluminium side plates attached to a 50mm x 250mm x 400mm cedar mounting block again with aluminium plate either side and all of this attached to 200mm long cars that will slide along the tracks. To be absolutely sure that it all slides freely (and not mounting the tracks perfectly parallel will affect this) I will wait until I have the cars and have made the trucks before fitting the tracks.

Yesterday I de-cored the dagger case ends and the hull panel cut outs and back filled the dagger case ends with uni rope and filling compound. It took me a few hours to complete all of the de-coring. I used the die grinder and burr that I purchased. It is a high speed air tool that rotates at up to 20000 rpm and takes bits with 1/4 inch shank. A burr is like a shaped (cylinder, Christmas tree, cone, ball etc) file that acts as a cutting tool. They are designed to grind metals so balsa is no problem for them but they do not remove the balsa fast. In fact along the straights I found it faster with the old fashioned chisel and mallet. I started on the starboard hull panel cut out first. I de-cored to about 20mm, but these edges are angled so in reality the depth was more like 40mm along the deep edge 20mm along the shallow edge.

Then when I started on the starboard dagger case, which I was decoring over the stern of the boat whilst standing on the steps. I did them there because the cases are heavy and I was too lazy to bring them down the steps then lift them back onto the boat again, a funny thing happened. I dropped the die grinder to the ground, a drop of about 8 feet. It fell on the bit, but being tungsten carbide it was un harmed. The die grinder I bought is an ebay cheapy. You can pay up to $200 for good ones, mine was $30. What had happened as a result of the drop was the shaft had bent just slightly so that the bit span off centre. I checked the bit in another tool to be sure the shaft of the bit was not bent but it was fine. It was definitely the tool. I cursed my bad luck (and stupidity for buying a cheapy) but had to push on. To my surprise the tool cut faster with the slight wobble of the bit than it did before. I couldn’t believe my luck.

With the improved cutting of the die grinder I used it to de-core the 2 case ends including the 25mm back edges. Again I cut to about 20mm deep. Then over to the port hull to de-core it, what took me nearly an hour on the starboard side took me only 20 minutes with the wobbly bit. The bit is able to take the balsa off the inside of the fibreglass but to get a completely clean inside glass surface with all balsa removed, a chisel is still the best method.

I then cut some uni to the correct size to make the uni ropes that will fill the de-cored edges. I found that 400mm makes a nice size rope to fill a 20mm deep by 20mm wide trough. I wet 2 of the uni ropes out and filled the edges of the cases. I then filled the rest of the gaps and overfilled with filler compound (resin and microspheres). I then placed a sheet of plastic onto the edges and placed a piece of ply onto the edges to keep the rope and filler firmly in place using heavy blocks to keep the ply down firmly.

This morning I found that the case edges had not fully set, not surprising as I did them at about 5pm the night before and I use slow hardener. It was firm enough to give the port one a clean up so that I could fit it into the boat. I cleaned up all of the sides of the case that will be taped to the bulkhead and also gave the bulkhead a clean up (light sand with the grinder to be sure there are no rough areas to upset the glass tape). Then I wet out a uni rope and pushed it into the hull panel de-cored trough and filled the rest with filler.

Then I ran a thick bead of glue along the front fact of the case and slid it down into the opening. I had a milk crate below the opening to stop the case at the correct height. I had slid the case into and out and back into the slot a number of times with the milk crate in place. Now that I had glue on the case the bloody milk crate slid out of the way and the case dropped to deep. I had to lift the case back out, jump out of the boat, replace the crate, and climb back into the boat and replace the case. This time it worked. Bloody Murphy! Anyway no harm done I clamped the case in place, adjusted it to square and plumb and tightened the clamp to be sure it would not move.
I then filled the rest of the gaps in the through hull with filler by using a scraper to push filler up from below until it had filled the gap and was coming out inside (which I checked by climbing the ladder to look). Once done it was time to tape. I started by glassing the base from the inside (the outside wont be glassed until it is set because the case is a mm or 2 proud of the hull in order to be able to grind it smooth). A little more filler from the inside and glass which I was wetting out on a sheet of plastic. I coved the inside of the case against the bulkhead by pouring a runny mix of coving compound down the join point then once it has reached the bottom I pressed a tape against the compound using conduit then applied a second layer of glass. I could reach the inside of the base from inside the hull by hand and coved as well as I could and pressed glass down into the wet cove and against the hull side and the case side. I then poured more runny coving compound over that and laid another layer of glass over that. Then finally the edge of the case against the bulkhead on the inside side of the hull (open to the companionway). This of course was the easiest to cove and tape.

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A double check of the square and plumb of the case and a smear of the left over filler on the outside joins to be sure there are no voids and I am pretty much done. The overfilled coving mix on the hull panel will be a guide when grinding that I am getting down to the copper epoxy as a reminder to be careful not to grind through the glass. I do have to take the copper epoxy off in order to glass the outside of the case onto bare glass, then a thin layer of bog to fair the panel back then recoating with copper epoxy to finish.

One down one to go. It was satisfying to finally have a case in. Next Saturday I will get the other one in.

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