Building Logs

Outboard wells and dagger cases.

After missing so much time it was good to get a long weekend and get 3 days of work on the boat. A day for me is only 7 hours though. Unfortunately the jobs that I have set myself for this month are time consuming for not much visual reward. But all jobs need to be done sooner or later so its best to just jump in and do them.

With the side decks off and the rear steps put aside for now the outboard wells are open again. I marked out 2 lines one each side of centre at 200mm in each hull. Then having decided at what height I wanted the outboard rails. I have bought some sheet track from McIntyre Marine. It comes to them in 2400mm lengths so I had them cut 2 lengths into 4 x 1200mm lengths. The plans only call for a 700mm track but I have an extra 500mm so that the outboard can be lifted on the tracks up through the open cover so that the outboards could be serviced easily from the steps and also so if necessary I can lift the outboards up so that I can reach the props for changing or removing nets or ropes tangled around them.

Once I had the height decided I could then mark the drill holes. The holes are 100mm centre to centre so marking them is pretty simple. Then I carefully drilled each hole through the glass and balsa but careful not to go through the glass on the other side. Glass kills blades of any kind very fast and balsa is very soft so you have to push the drill hard to get through the glass then all of a sudden you are through and then you have to pull up fast then you can push to the other glass and you can feel it (you would have to push hard again to get through the glass on the other side, and the other side of this bulkhead already has an extra layer of glass). Once all 48 holes were drilled I had to de-core the balsa between the front and back glass.

As anyone who had built a timber cored boat, whether the core is balsa, cedar, ply and probably also true for non timber, you need to keep any moisture out of the core. It is critical to building a boat that will last. So wherever you have a through hull such as a bolt, pipe or any exposed edge such as hatch lids, you have to de-core and back fill with filler, either glue or coving filler (microfibres or microspheres in resin) which create a barrier that stops moisture reaching the core. The most common way to do this for a through hull bolt is to drill a way oversize hole and fill it then re-glass the oversize hole and then when it is set you redrill the correct size to end up with a hole through the fill.

I have learnt a method (thanks James) for balsa that is a bit easier. It is to drill a hole through just the first layer of glass and the balsa. Then using an allen (hex) key in a drill and to push that into the balsa through the hole and then to slowly turn the drill until the key has cut a path through the balsa. Then using speed, the key is used to to ream the balsa out of the core all around, by moving the key around the hole you increase the reach of the angle on the key and by pulling it against the front glass and pushing it against the back glass you remove all balsa from the now 40mm hole inside the glass. Then push a blower nozzle in and give it a burst but be careful as balsa shavings will exit that hole at velocity.

There are 12 holes in each track x 4 tracks so with 48 holes this is a time consuming job for very little to show for it, but again as any cored boat builder will tell you, decoring is one of the most time consuming chore in the build. The next task was to fill them all. My method as I have outlined earlier in the build when making the hulls, is to mix the glue/filler and put it into zip lock clear plastic lunch bags and cut a corner off to create a piping bag and squeeze it into the hole until it overflows out. Then using a scraper I scrape it back flush to the glass. I ran out of time (Jo had arrived to pick me up from the shed and rather than finish I decided to finish the next day, which turned out to be a mistake). So I got all of them done in the port hull and got about half done in the starboard hull.

The intention the next day was to grind down the set filler back to smooth and flush with the glass ready to re-glass over (with this method you only have to glass one side, the other sides glass is intact) and to fill the rest of the holes and glass them over wet on wet. In fact when originally planning my day yesterday I had intended filling all the holes and over glassing them wet on wet, all of them, which I why I so readily decided to stop filling the night before as it was always my intention to fill and glass wet on wet. Mistake. What I had forgotten was that as the filler/glue sets it expands a little and in a tightly confined space it pushes glue out through the hole, which in normal circumstances is no big deal but with wet glass on it pushes the wet glass away from the surface glass around the hole leaving air under the glass and not adhered to the substrate glass. Not a disaster as it is only about a quarter of the holes and I will simply grind the lifted glass off again and re-glass them. But a lesson for next time. It is to be 2 processes from now on, let the fill set, then glass later.

The plans call for a layer of glass each side of bulkhead 7 (the rear bulkhead) and as it has the uni rope arc embedded in it and also because I have also glued panels back into the bulkhead to transform it from a walk through to and enclosed cockpit I readily followed the plans. As I mentioned earlier I had already glassed the inside of this bulkhead prior to making the cockpit furniture.

I measured and cut the glass ready to apply and got on and applied it. With the inside I hung the dry glass with spring clamps and brushed resin onto it to wet it out. This is a messy method as anyone who has attempted to brush resin to wet out will attest. Wetting out is not like painting, you need much more liquid to get the glass wet through so that it will penetrate and adhere to the substrate glass below, so it is inevitable you will drip a lot of resin. It is also a time consuming method and often results in too much resin.

So this time I wet the glass out on a table with plastic sheet, rolled it up and then hung it out wet (again using spring clamps) and using my hands and a consolidation roller I adhered it to the panel glass below. This method is much neater, much easier and perhaps a little faster. Once I had the port side glassed I applied peel ply. The reason I did this was twofold, first to soak up any excess resin but more importantly to avoid having to sand it later. I will be gluing and glassing the ply pads on and then eventually the rest of the well will be white resin coated to seal and smooth the well so the peel ply will pre key the surface for the next layer of resin.

Then when I did the starboard glassing I just had to first fill the remaining drill holes, which I quickly did (took about 20 minutes). I then went about wetting out the glass as I had done on the port side and applied it over the holes including the dozen or so that had setting glue in them. Once that sheet was on I started on the next sheet and as I hung the wet glass I noticed the glass lifting from around some of the wet glue holes. I tried pushing it back down and noticed how hot the now nearly set (through exothermic reaction) area around the holes had become. I could not get the wet glass to stay down all over the holes and there was a pronounced mound there now. I tried apply more resin to no avail. I will need to grind it off later as mentioned earlier.

Again the time flew by and the day had gone with just the glassing of a bulkhead done.

Today I set about trimming the dagger case on the port side, which had already been cut through the hull and side decks and to cut the starboard dagger case into the hull and side deck. This is a difficult (not technically just physically) task because the cases are quite heavy and go through the angled chine so the shape is not as straight forward as it would be on a flat hull panel.

It was however somewhat easier than the first one, which was a series of trial and error (fortunately not much error because starting with a too small hole and slowly getting it big enough has the end result of an ok fit). This time, using the hole of the port dagger case I traced it onto a piece of 3mm mdf and cut that piece out. I marked the centreline onto the template, reversed it for the other hull and I had a stencil to cut out to. The centre line is not actually centre on the template because of the angle of the chine the case goes through the line is offset. With the line pre-marked on the stencil and the case centreline already marked on the inside of the hull it was easy to place the stencil correctly and trace out the cut-out shape.

I also tried a different cutting method. Last time I used a jigsaw and within seconds the blade was blunt and smoke was pouring out of the cut as the blade gets very hot cutting the glass and burns the balsa. This time I traced the stencil onto each side of the hull panel (inside and outside). To get the stencil in the correct place outside I drilled holes on the centreline one against the bulkhead to mark the front position and then 3 more along the centreline. Then using the drill holes as a guide I ran a straight edge to mark the centreline and placed the stencil, lined up with the first hole as the front and traced the shape onto the other side of the hull panel. Then using a grinder with a solid cutting disk I scored the glass through both sides leaving just the balsa so that the jigsaw only had to cut the balsa and the glass edges guided the jigsaw blade. It was a bit tricky around some of the curves but overall much easier than trying to cut the entire panel with the jigsaw.

I used the same technique when trimming the dagger cases. Once I had the dagger cases roughly in position through the hulls and against the bulkhead (BH5) I marked the outside hull line with a marker pen, then removed each case (they are quite heavy because of the extra uni layers I applied to them for added strength) and scribed along this line with the edge of a grinder blade. The outside of the case has about 5mm of glass at the base so a jigsaw would have really struggled to get through it. But with them already cut the jigsaw had a much easier time of it. Once I had the angled case bottoms trimmed I cleaned up the angles with a grinder and replaced the cases in their through hull holes to see if the trim was close. Within 10mm is close enough. I will remark them for a more accurate final trim, then remove them again to de core the edges to be re-filled with uni rope and filler (uni rope to a depth of about 20mm and filler for the last 10mm or so) then when they are glued and glassed into the boat I can grind back the few mm of overhang and glass them from outside. The edges of the hull panel will also need to be de-cored and filled with uni rope.

sb dagger case trimmedsb dagger case side deck exit

Hopefully I will get the dagger cases glued and glassed in next weekend. Then I will make the grey water tank that will fit behind the port case and the cupboard that will sit behind the starboard case.

You May Also Like