I would set the jig upside down, that is, keel up, to true the hull. I can't see how you could get a real good idea of the trueness of the sections unless you can use strips along defined lines like the chines and the gunwales. The bottom of the hull is the most important part of the boat functionally. You will be sanding it fair -by hand. If it is out 1/8 then you will loose 1/2 your strip or have to put a lot of fairing filler in the hollow. You will quickly realize as you place strips on the bottom surface that you don't have to worry about what it looks like or how many staples you use or whether the joints are perfect -just fair. The topsides and the deck are another matter when it comes to looks. The topsides must be pretty fair because that is where the light will be reflected along a long straight run of strips. Making the bottom fair will automatically do the topsides. The deck has to look good but has so much clutter breaking it up that it doesn't have to be so perfectly fair. A few hollows and slight bumps might never be noticed by anyone but you, unless you point them out. That's why I'm just going to trust the lay of the strips on the deck. Shim the gaps in the section that is a bit low (#11), and just get the joints right so that people focus on how the wood looks seamless. Trusting the strips themselves will make it fairly close anyway. People who look at it won't even know it's not perfectly fair with all the rigging and non-skid patches on there. The trickiest parts will be the angle joints on the deck strips at around the mast step and back from the there. People are only going to look at the joints on the tank top and how the decorative stuff is nicely joined. It's worth spending a week of 2 hour stints to get that right.
Warren,
I'm not sure if Bram answered you question. I understand you are asking how to true the hull??. It's something you want to get right! Double check section 1/2 is at position 1/2 not position Zero!!!!
Here is how I did it. I cut template routed sections so before you start mark all the centerlines on both sides and mark all the waterlines out to the chines at least on one side on all the sections.
Take the central strongback, lay it on a bench, mark the position of the waterline (measured from where your waterlines cross your sections central strong back holes) for a forward section and an aft section (#13 and #2 should do).
Use a laser line to line up the forward and aft waterline marks and make a pen or pencil line along the laser line on both sides of the strongback that is a straight line between both forward and aft waterline marks. This is the datum line along the strongback. Do likewise on the top of the strongback (when I say top, "top" is the side closest to the bottom of the boat as you will build the hull upside down). If the strongback has a little bow you will see it and be able to use wedges to correct it.
Set the sections and strongbacks up and put them all together, use wedges to align reasonably the centerlines and the waterlines of the sections to the central strongback datum lines. (I used a pack of white cedar wedges from home depot these can be easily snapped off and are soft cheap and easy to use.).
Then to lock them all in position start with section 10 the widest. Level it with a bubble level (check both sides) and set the wedges to center the central and then the outer strongbacks in their holes.
Center the outer strongbacks in the holes of their most forward section (I think it is #7) Level section 7 with the bubble level.
Check section 13 likewise and see that it is level. You may have to readjust section 7 wedges now. But fuss with this until it is perfect.
Place 4 plywood support legs on the outer strongbacks at section 7 and 13 (and also at 10 if you want). Use hot glue, so that the assembly will remain level and not twist if you lean on it. You will lean on it a lot later.
Set a laser line on a stand about 2 feet over the transom, shine it down the center line. Adjust 13, 10 and 7 to be on the line and check the line is also on the datum line of the central strong back.. (My central strong back was a bit bent at the bow so I used string line to tension it and bring the strongback into column with the laser).
Place a sacrificial strip down the outer gunwale edges. Adjust and re-adjust the wedges to bubble level all the other sections starting moving out either way from section 10.
At the same time as leveling all these sections put a strip over the top on the centerline to set a fair line to the height of the sections. I had no trouble at all, except for section 4, it was 1/8th out. I had to manhandle it down with wedges at the bottom, none at the top. Take off the edge strips and place another strip there but Staple it only at a few sections. Sight the edge strips and the centerline strip they all should just touch all the sections. Flip the centerline strip over and check again and replace it with another strip to be sure the strip is not biasing the placement. I cut a lot of particle board spacers to stabilize the sections lock them in place and to make sure they were at 90 degrees to section 10. I put them on the sides of the strong back, and at some of the front sections I set a few parallel to the strongbacks but as far apart as I could. Like mini side strongbacks.
I glued them on with wood glue and hot glue. Hot glue for immediacy so that the job doesn't take forever and a million clamps or worse, Screws, and also slathered on wood glue to set over night and forever.
When I turn it over for the deck I will use a strip as a shim because I will not be able to or want to move section 11.
Place the 2x2 strongback in the forward sections before they are set in place and set the horizontal and vertical height by sight fairing the strips at the gunwale and keel..
Hope this helps. I took 2 -3 days to set them up. it was a pain because of the bend in my strongback. I should never have used slightly warped ply to build them. MDF would have been better if a little heavy.
Greg