Hello, I have built two HWS -- but they are very heavy. I want to use the minimum weight material for the spar and ribs, as well as the deck and under surface ( what thickness for glued together strips - not ply wood), and rails. Please recommend the combination that might yield a light but durable board about 6 1/2 feet long. Thanks, Bill
Bill - hollow wood surfboards tend to be heavy, maybe not onerously so, but definitely when in comparison with modern lightweight foam and fiberglass boards. I don't think that the framework (ribs / spine) is really a significant part of that weight, but I suppose it could be depending on the materials and design.
My thinking is to keep the cross-members (ribs in most cases) light, but closely spaced, allowing for a thinner decking, which is, in my opinion, the most significant part of the weight of a hws. If you want, go a bit stronger with the ribs in the standing zone.
Here is an example of a lightweight laser-cut framework, that is in my opinion, too widely spaced. This was a kneeboard (not mine) and the ribs broke in use. I know I'm probably the only one who will say this, but I think 3" o.c. is a good spacing for this light of a frame, and I wouldn't go quite so spindly on the verticals webbing.
Here is a photo of one of my boards, with the chords at 4" o.c. if I recall correctly.
and here's one of mine with the spacing at 3" o.c.
If you're going to use standard ribs, I would go about 3/16" thick, maybe 1/8", keep them relatively light, and spaced at 3" on center. The you could go 1/8" - 3/16" on the skins, to keep the weight down.
These are just relative suggestions, much depends on your specific design, and materials. If you're using balsa, you need to keep in mind that it is a much weaker wood than say redwood or cedar, and build accordingly. I haven't used paulownia, but hear that it is an excellent wood for keeping the weight down on a wood surfboard.
=)
I have been using 6mm okoume plywood (~1/4") for center and frames. I have my frames set at 8" oc… Seems to work pretty well…
Here is my latest: