On Line Manual:
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4: Strongback & Molds
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I really don't know where the term "strongback" comes from - other than it is a
boat builders word for the platform upon which one builds a hull.
The least complex strongback for smaller
strip-built boats often takes the form of a ladder and is constructed of 2x4 stock. Be
picky about the stock you buy for a strongback. You just don't want
to start a fine boat using twisted 2x4s.
| The photo to the right is the
strongback I used to build the 10' dingy "Tasha" - one of the hulls being used
to illustrate this manual. Because I did not intend to build more than one of these boats,
the strongback was kept simple and disposable. The hull used four molds, or forms, plus a
stem mold and the transom. Crosspieces are two feet apart and are lag screw fastened. In
the background are the uprights that will support the transom. In the foreground is a
convenient tool shelf. On the tool
shelf in the photo is a chalk line that has just been used to mark the center of all
crosspieces. |
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Of course there are much more complex
strongbacks you could use. For years I used a three foot wide bench with casters all
around, a top of 3/4 inch ply with bolt holes drilled at proper locations for each of the
hulls I was building, storage racks built under for different lengths of strips, power
outlets at each end, and custom bins for each tool.
But for symplicity, stability, and low
cost the ladder strongback really can't be beat.
| The length of the strongback
for your particular project will be given, or at least discussed, in the plan, as well as
the correct placement of the crosspieces. It is important to pay special attention to which side of the line the
designer wants the crosspieces placed. It is easy to make an error here, so most of us go
on and on about it. |
sbk draw 1 |
| To the right is the center
portion of the same design as above, for an 18' canoe, that illustrates well what I am
getting at. Note that mold #6 is
centered on the line that is the mid-point of the strongback.
But the adjacent molds are placed beside
the line that is 18" from the mid-point.
All this makes sense if you consider that
each mold is a cross section of the hull at a specific point. |
sbk draw 2 |
| The final step before we
begin tracing the molds from our plan to a sheet of plywood or particle board, and sawing
each of them out, is to mark the center line of the strongback on each crosspiece. As shown to right, the centerline of each mold is
set on the centerline of its crosspiece and firmly fastened to the crosspiece with screws.
The mold you see here is what I call a
"elevated strongback line" type. |
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| The plan sheet that contains
the patterns for your molds will most likely show them on either side of a centerline. You
can trace each pattern to some poster board and from there mark each one on the plywood or
particle board. Or you can cut them right from the plan sheet, largest first. Each pattern, except the stem, will be half of the
full mold. Just mark a centerline on your ply, mark one side of the mold, flip the pattern
over and mark the other side, and lable what mold it is..
Cut each one out with a sabre saw -
carefully - and you are ready to mount them. |
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Copyright 1998, 1999
by Lew Miller, DBA Marlew Publishing.
Image copy granted for personal use. Please credit source.
