: I have been considering a 2 X 4 strongback made of plywood, a 2 X 4
: inch aluminum extrusion and schedule 40 plastic pipe.

: The 2 X 4 plywood is pretty straightforward and inexpensive. It
: would not take too long to make--maybe a couple hours. Some care
: has to be done to make sure it is straight.

: The aluminum extrusion is straight and ridgid, but will probably
: approach $200. If anyone used a 2 X 4 rectangular extrusion, let
: me know your experience. If other than 2 X 4 extrusion is
: suggested, I would like to hear your experience.

: I have heard of people using schedule 40 drain pipe (4"?) as a
: strongback. It would seem to be a good idea. It is quite ridgid,
: VERY cheap (less than $10 for a 10 ft section). I am not sure
: the best way to attach the forms, but it does not seem like it
: would be a big deal. The 4 inch sched. 40 is a little over 4
: inches in diameter and would require some modification to the
: strongback dimensions in any plans I bought. If anyone used
: schedule 40 as a strongback, I would be interested in their
: thoughts on how it was modified to attache the forms and stem
: pieces, if 3 or 4 inch was used and any other feedback.

Even schedule 80, roughly twice the wall thickness, isn't rigid specially in long lengths.

I still don't see the point of an internal strongback, the external one is pretty simple and can be used for lots of different boats.

Bill H.