Thursday, February 01, 2007

Layout and Cutting of Bulkheads

I've had only short blocks of time yesterday and today to work on the project, and I've spent most of that time carefully measuring and drawing out the bulkheads. These are a bit more time consuming than some of the simpler parts like hull panels. It's critical to get all the measurements correct on the bulkheads, as the hull shape will not come together correctly otherwise and imperfections in the layout or cutting can cause unfair curves in the hull sides. The bulkheads are lofted out based on a centerline and sheer line, and the sides are sprung to a slight curve that varies with bulkhead position. In addition to these critical lines, there are bunk levels and floor levels, notches for the topside stringers, and inspection plate cutouts as well as the bunk openings in the main cabin bulkheads. I started with bulkheads 1, 5, and 6, as these are all deck level and do not include cabin lines in their measurements as do bulkheads 2, 3, and 4. After lofting and cutting out the first set, then carefully trimming and shaping them to the marked lines using a belt sander, I used this set as a pattern to make the bulkheads for the second hull. Shown above are both sets of bulkheads 1, 5, and 6. After all these are cut out, I'll make and install the bunk and floor bearers and epoxy coat both sides in preparation for hull assembly. So far it's been too cold for epoxy coating this week, with lows at night ranging from 21F to about 30F, and the highs in the daytime 50F or less. Tomorrow it's supposed to be a bit warmer.


tsunamichaser said...

Nice proogress. When I was assembling the first hull I discovered that bulkhead 3 was a little naorrow near the top. I ended up adding a 1/4" wedge here, and then glassing it in. It's all hidden in a good strong fillet with 3" tape on each side. I checked the other bulkhead and I had cut this right. The hull is somewhat plank shaped near the top. This might be the result of Wharram simply stretching the T21. What I'm discovering is that the hull has a short straight section to it. At the keel it is about 2 1/2 feet long and on the upper hull side it is closer to four feet. I think that if I was starting fresh on this priject I would strip plank the hull with 1/4 by 3/4 edge glued strips. Yes I know a whole mess of work but the hull would turn out fairer I believe.

Scott B. Williams said...

Thanks Thomas,

Yes, I found similar issues when building the Hitia 17, but I think that's true of any stitch and glue boat. You just have to work out the fairness as you go. You'll notice I'm leaving an extra straight panel of wood above the sheer level on all the bulkheads. I'm planning to do the same on the cabin bulkheads, building only to the sheer level until I decide about any slight changes in the cabin profile above the sheer level. This will leave my options open for a slightly raised deck, as I mentioned to you before, but I can always go back to the standard cabin height if I decide I don't like the way it looks after springing a batten through it.

I've done some strip planking, and it sure is tedious. I don't know if I'd want to do it on a boat this size, but I agree, it is a way to get fair curves.