2016.04.26 - Template Woes
Getting the ribs installed is taking quite a lot longer than I expected. Firstly there is nothing to hold them in place whilst the glue is drying and secondly two of the ribs on each side are going to be the place where half bulkheads are to be fitted. I decided that the best thing to do was to make the half bulkhead that will be fitted just forward of the bolt through the centreboard case upon which the centre plate pivots. This will act as a structural reinforcement for the case as the crosswise wooden slats that did the job before have been removed and also as a reference line for the rest of the ribs on that side. Once I have the bulkhead cut out I could draw a line on the hull where the aft edge of the rib should go. Only it wasn't as easy as that. The bulkhead should be at right angles to the centre line of the boat and the top of the bulkhead on each side should be level with the water, or where the water will be when the boat is floating. As this is the first thing to be installed, there's nothing to reference it against except the centreboard case. So where exactly is ‘at right angles to the entire line’?
I put a screw in to the breasthook at the front of the boat and tied a piece of string to it. The string was long enough to reach over the back of the hull. Next a straight piece of timber was placed across the hull resting on the gunwales above the centreboard bolt and moved to the correct point fore and aft by using a plumb bob from the timber to the bolt. This meant that the centre of the timber was correctly positioned. The string was pulled tight, placed over the point where the timber met the hull on the starboard side and a pencil mark made on the string at that point. The string was moved across to the port side and the position of the pencil mark noted. If the timber, hull and pencil mark all met then the timber not only was in the correct place fore and aft but it was also at right angles to the centreline of the hull.
It wasn't of course and I had to move the timber around little by little until everything was in the correct place.
Now I could use the plumb bob from the timber to mark points on the hull that were directly below the timber and by joining these up I had the line on the hull where the bulkhead was going to be placed.
So far, so good.
The next job was to try and cut a piece of cardboard that fitted against the hull along this line. I tried several methods. Guesswork, spile and flag, scraps pieces of timber clamped to the approximate shape, scrap pieces of timber stapled together to the approximate shape and none of them worked for the very simple reason that there is nothing to hold the proto-template in place stiffly enough to draw a line on it.
In the end, with Tina's help I did manage to get a curve on the cardboard that was close enough, within about 1mm or so and that will just have to do.
But that is just the curve of the hull. I still had to do the bit that fits against the centreboard case as well as the top. That was a lot easier. I could sit in the boat with some cardboard and a pair of scissors and cut the correct shape. I glued it to the curved template with hot glue. There’s also another bit glued to the template, again with hot glue, as I reused one of the failed attempts to get the correct curve and the piece wasn’t quite big enough.
It's taken three days so far and I still haven't got the bulkhead cut out and I still have three more to do. Hopefully the ones on the port side will match near enough the ones I'm cutting out for the starboard side.
The intermediate ribs will be easier to do since I will be able to measure from the one to which the bulkhead is attached.
But my, oh my is this a trial.
There again, I don't want to cut out a bulkhead from the expensive marine plywood I bought and then find that it doesn't fit.
Loads of photos taken over the last few days.
A screw in the centre of the breasthook as an anchor for the string.
Timber, hull and mark on string aligned on the starboard side.
Timber, hull and string aligned on the port side.
Plumb bob down to the correct point on the hull.
Closer view of the plumb bob just to prove that I wasn’t fudging it.
And the proof that the timber is just about level. Since it is resting on the gunwales, the hull must be just about level as well.
Trying the ‘put it all together with clamps’ method. Failed. Pick it up, no matter how carefully and the whole thing distorts.
Trying the ‘staple it together trying not to hit your fingers’ method. Failed. Not enough reference points and nothing to hold extra bit with to get the reference points.
Try the ‘guess’ method. Failed. I don’t even know why I tried this one.
Try the ‘spile and flag’ method. Failed. Not enough reference points. See above.
Try the ‘get Tina to hold it while I draw the lines’ method. Success as you can see. The two extra bits are held on with hot glue, what an amazing invention that is.
Another view of the correct curve ready for the top line to be marked.
Given that the template was not securely held, the four pencil marks are pretty much aligned. Here are three of them…
…and here is the fourth.
The cutting line…
…and the cut.
And this is the almost completed template.
A quick check to see how it fits on the other side and it is pretty close. I may not bother to do a second one and just thickened epoxy to fill the gap. We shall see.
The last piece of the template cut away. This will allow any water that does get in to run to the lowest part of the boat where it can be mopped up.
And there it is, the completed template.