bending plywood question

[wscherf]

We all know that plywood can be bent (not "tortured") over conic sections. Thus, V-bottom boats using a single sheet of ply on each side of their keel often have curved section shapes toward the bow - think the Core Sound 17 &20 or Arch Davis' Ace 14.

However, I noticed that Dudley Dix's Cape Henry designs, of 19 and 21 feet, while using a wide plywood garboard strake, show straight sections at the bow. WaterCraft Magazine, doing a how-to-build-it series on the 21 footer went into some detail on fitting the 9mm garboard strake. They kerfed it and steamed it, but did not mention torturing it, that is; making it assume a non-developable shape.

I thought that torturing ply was only workable on very light structures ( Paul Gartside's Flashboat). Anybody have any light to shed on this?

[Bruce Hooke]

"Torturing" is a matter of degree. Even thick plywood can be forced a bit, as anyone who has applied your typical piece of somewhat warped CDX plywood to a flat surface knows. I'd speculate that on the designs in question, where we are talking about a piece of plywood that is only maybe 12 or 16" wide in the area with a lot of twist, and where apparently you have to kerf and steam the wood to get it into place anyway (both of which would allow for more "torturing"), any small amount of curve that should in theory be present in the sections is small enough to be a non-issue...

To advance the discussion, here is a picture of the bow of the Cape Henry 21. The picture is borrowed from Dudley Dix's web site. (http://www.dixdesign.com/ch21.htm) The boat was built by someone named Gary Wallis in the UK.

http://www.dixdesign.com/ch21wallis1.jpg

[WayGray]

When designing a developable bow shape, the bow sections can be either straight or curved depending on the underlying curve and the type of projection. Torturing is not required if the curve and projection are planned properly.

From the picture on the Cape Henry 21, I don't see anything that would necessarily require torturing.

[bainbridgeisland]

Agreed. Bending plywood around a conical or cylindrical shape is not usually considered torturing. Sawing kerfs may be needed if the plywood is too thick to take the bend but is not terribly effective when trying to torture plywood around a non-cylindrical or non-conical shape.