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7. Strongback setup

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I have decided to build a plywood strongback since it will be used for the construction of quite a few kayaks. The whole piece is made from one and a half sheets of 3/4" plywood. The layered plywood is more stable and resistant to warping in the long run.
If you are building only one kayak, you need not go this far to make a flat and straight foundation. You can use 2" x 12" lumber or any combination of plywood or even particleboard. The whole objective is to build a flat table surface 12" (30cm) wide and 12 ft (3,65m) long. You may already have a surface like that available (one plank attached to an aluminum ladder, a plank on a garden wood bench, a plank on a shop bench or a table etc...) What really matters that it is straight and with minimal twist.
As a standalone profile, the "T" shape uses the least amount of material to build an accurate strongback. The top edge of the vertical beam that supports the horizontal piece was cut perfectly straight. Use a thin string or fishing line and a pencil or a magic marker to establish the cut line. Trim with circular saw.
The receiving piece for the strongback is leveled laterally (side to side) and screwed into the horses. The attachement of the second piece will give you the opportunity to level the strongback longitudinally.
Note that the table rests on the top of the receiving piece - nice and horizontal. The slot was cut a bit wider to allow simple, quick but secure fastening with a wedge. Adjustment and disassembly is a snap.
Ready for hull station blocks.
Establish and draw a centerline on the strongback first using the string method. Lay out and fasten the station blocks according to spacing directions in the plans. Starting with the middle station centered and level, the two remaining forms are easy to align and affix.
Align stations by the centerlines and the horizontal lines.
Here is a clever and quick way to align the stations if you do not trust your eyes or the station configuration makes it hard to sight all three stations at the same time.
In this instance the two end stations are installed first and leveled, then the strings are stretched from the alignment lines between the two stations and then the mid station is easy to align to the strings as well as the centerline. This picture was sent by Cristiano Monzillo, builder of the Cirrus .

A couple hours later, the accurate strongback mold is ready to receive the hull plates. To get to this stage will take about one afternoon. The cumulative time saved thanks to this setup will be measured in days over the length of the project.

A precise strongback assures:

  1. Perfect symmetry and shape of the kayak regardless of your skill level.
  2. No "second guessing" of your work.
  3. Rock solid platform to work on
  4. Frees both hands to wire, align, fillet, sand, scrape, glass, epoxy coat, squeegee, cut and everything else you need to use both hands for.
  5. No temporary fastening solutions to waste time on and to get in the way of the work.

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Last page update: 11 January 2020