: Before screwing together my ladder-style strongback, I have it clamped
: together. It has taken a bit of clamping to get a little twist out of one
: of the 16-foot 2x6s running along the side. The resulting strongback is
: slightly twisted with one corner raised about 3/8th of an inch.

: My question now is -- do I accept this and adjust the station molds to keep
: the boat's shape true, or do I scrap the problem 2x6 and buy another
: 16-foot board to use for my strongback?

Sounds like one of the boqards is a bit warped toward one end.

Here is how you solve the problem with a minimum of work. You may be able to do this while the project is clamped together, or, you may have to unclamp things for a while and then reassemble.

First, lay the board flat on its side and stretch a string along the length. Tap brads 3 inches from what will be the top side of your strongback near both end, wrap the string along them so that the string is to the top or right of both brads, and gently pull the string taut. Since the board is laying on its nominal 6 inch side, that strin should rest completely in contact with the wood, and pe perfectly straight.

Get a can of fast drying spray paint in a bright color. Hit the discount stores, cheap stuff is just fine. Hold the can of spray paint 1 to 3 feet above the board, keeping it directly above the string, and let spray. Move the can rather quickly. You just want a light mist to fall on the board. After one pass over the length of the board, go back and mist it again. Let this rest for 5 minutes so that the paint soaks into the wood -- it doesn't have to be dry -- and then remove the string. You should be able to see the "shadow" of a perfectly straight line running along your board, which is where the taut string blocked the paint mist. Repeat the process for your other board for your strongback.

Some people use a chalkline to make these long, straight, reference lines, but the movement of the chalkline can throw off the accuracy by an 1/8th inch in the center, and the chalk rubs off too easily. The paint stays on there as a nice reference. Your string did not go to the ends of the board, but you can extend the line with a pencil and a straightedge.

Now you can take a short ruler and go along your 2x6s and see how far the actual edge of your strongback deviates from a straight line.

Correcting the curvature and getting a nice straight edge on the top side of the strongback board can be done in a variety of ways. You don't have to worry about the bottom edge being straight, you are not going to align anything with the bottom edge.

The most direct route is to plane off the excess wood. Use a ruler or a home made gauge block. Set a block of wood on your string shadow line (let's call this the centerline) and make a mark on the edge of this block where it lines up with the top edge of your strongback. Move this gauge block a a few feet down the length of the strongback piece and check to see if the mark still matches up with the side of the 2x6. IF the mark is touching the 2x6, then this is an area where you have to plane off some wood. If the mark is not touching the 2x6, then obviously things are a bit too thin there already. You can either shim in the area, or, make a new mark on the gauge block. Eventualy you find the narrowest spot in the board and have a corresponding mark on that gauge block. Now you can slide it along the length of the 2x6 one more time and transfer the last mark onto the 2x6. Now just plane away the high wood until you come down to this mark.

That might be a lot of planing. If you know about where you are going to mount those frames, you can just remove the excess wood in a smal area with a chisel, router, or by making multiple, shallow crosscuts with a saw. If you cut too much, you cana put in a shim when you mount the frame.

Save your gauge block. When you go to attach your crosspieces on which you'll mount the forms, you can use it to see that the crosspieces are all the same distance from the centerline.

When you assemble your strongback, level the centerline. Cut 4 pieces of wood that are the same width (A 1x4 will do) and nail them to the center lines on both boards for your strongback. A level across these will get both centerlines level and at the exact same height above the floor, even if there are slight differences in the top heights of the boards. If you want, you can just shim all your crosspieces to be level, and up to the height of these boards. This can save you some of that planing, but there might be a lot of shims.

: By the way -- maybe I should say -- I plan to build a Cosine Wherry. Ok, it
: is not a kayak, but i have a SOF baidarka, and I would like a boat I can
: take a passenger out in.

Well, when you row you turn your back on the scenery and face the stern seat, so if the passenger is prettier than the scenery, I guess rowing beats paddling.

Happy building

PGJ