Doing this kind of work (bulkhead alignments) is when I realize what a crap job I'm doing: none of the bulkheads fit just right, and gaps are everywhere; this isn't new of course, over time I've started to figure out that the boat, when completed, will be a huge amalgamation of compromises and "split the difference" compensating errors. That said, don't let me discourage anyone else from building.
Before I get into the bulkhead details, I have a mea culpa. I've been reluctant to admit it here on the blog, but my lower hull half lamination did in the end suffer a bunch of bubbles (I didn't actually see them until the next day). It was a hot day when I did that work, although the temperature was fairly stable - still haven't pinned down the reason for it. So Tuesday night I sanded them all out and laminated a bunch of patches over the holes:
I have to admit that the devil in me kept saying "why bother patching them, it's just a few bubbles, they won't hurt nothin'" - but my better side finally won out. The good news, is that the lamination I did on the upper hull half turned out spectacular! Not a single bubble anywhere to be seen. As mentioned before, the differences were a) cooler temperature; b) pre-wetted the foam; and c) used Fast hardener. I can't always control the temperature, but I will definitely be pre-wetting the foam from now on.
For the bulkheads, I wish I could say that I was able to whip out a laser level and a protractor, do some mystical math tricks, and then line everything up with millimetric precision, but it never seems to work that way. So please don't laugh too hard, when you see my primitive methods.
Here I'm digging a hole in the side of the boat right over form frame #5, in order to expose the gunwale line (for aligning the fwd beam bulkhead):
Tip: don't mount the @#$*&! battens right over the gunwale reference on the form frame. And keep a sharp razor blade handy -- thick, cured laminate (due to the overlaps in this particular area) is tough to cut!
To locate the the fwd edge of the fwd beam bulkhead, I made the following alignment thingy (to call it a "jig" would be too grandiose):
The 3/8" ply, plus two popsicle sticks, makes exactly 1/2". Or close enough, anyhow. I then carefully mounted this utensil so that it poked up thru the hole I'd made above, aligned with the edge of the gunwale line:
And from the top:
The other reference point for the fwd beam bulkhead, is that the fwd bottom corner should be 9/16" in front of frame 5's fwd face. For that one, I decided to take the easy way out and drill a small hole from the outside of the mold, at the edge of the frame; I then marked a small line the appropriate distance in front of it:
Looking down, here's what the popsicle tool looks like:
After I had the above two reference points, it was then just a matter of jiggling and trimming, until I had the bulkhead reasonably aligned and vertical; I then marked it for later taping:
Now, let's all pray that I've got this thing aligned accurately enough. Count of three: 1, 2, 3 ... pray!
Now for the plumb bob part. I borrowed one of these from my neighbor (thanks Scott!); it's a big, heavy, yellow thing with a really sharp tip, looks a bit medieval in fact. I needed it so I could locate the aft edge of form frames in the middle of the hull, by hanging it from a straight edge (my level, in this case) that was aligned with the form frames at the keel and deck center line. E.g:
Once you have the frame aft edge marked somewhere in the middle, you can easily line up the bulkhead; the main cabin aft bulkhead turned out pretty good I thought:
However, here's that gap by the deck that I mentioned before; I have no clue how this showed up:
I'll just fill it in of course, and hope that the starboard side has the same problem so it lines up correctly. :-)
I have not yet marked the final location of the aft beam bulkhead; however I think I came up with a cool way to locate the aft edge of its form frame, by using a ladder to hold up the deck-side edge of the level, and locating the level (fwd and aft on the deck\ladder side) by dropping the plumb bob right at the frame's stub aft edge:
You got to admit, a plumb bob is a pretty cool tool!
Once I had it perfect, I clamped the level to the ladder (no-one better bump the ladder though - I had to shim up the legs with scraps of foam), and was then able to move the plumb bob back over the hull to locate the frame edge farther inwards. I didn't get around yet to digging a hole over the gunwale line, but I suspect I'll end up having to drill through a batten to expose it, just like I did with the fwd beam bulkhead.
Anyway, I hope this will give other builders a few ideas on how to locate these bulkheads (and I'm sure my techniques can be improved upon).
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