2) I'm over 210# (not sure how much....been afraid to step on the> scales after>> this winter...), 65 years old, extraordinarly clumsy, uncoordinated,> inflexible>> to the extreme, and not in particularly good shape - but I can uphaul> my>> Starboard 123 with a 7.8 on it anytime, anywhere - no problem.>>

Given the above, it seems like very few people would need anything> with volume>> much over 120 liters.>>

That begs the question: "Why do we have 140-150-170 liter boards?> Why not make>> something with the same bottom shape/area in 120-or-so liters and> have thinner>> rails?" Less material, easier to carry, better looking....maybe> even better>> turning.>>

Unencumbered by any real knowledge, I'd guess it's a marketing> reality. The>> buyer can grasp a series of boards that have increasing displacements> as they>> get "larger"... but would have trouble comprehending boards of> more-or-less>> similar displacement but different areas/shapes.>>

-- >> PeteCresswell>

However, If we are to look at vertical bending of the board along its>> nose-to-tail axis we see that increasing the board's width results in a>> linear increase in board stiffness, but increasing the board's thickness>> results in a cubic (power of 3) increase in board stiffness. So>> theoretically, doubling the board's width results in double the bending>> strength, but doubling thickness results in 8 times the bending strength.>> So, small increases in board thickness could result in significant>> increases in strength and stiffness.>

Unlike a true mold, where the material is laid up or sprayed onto the >> sides of the mold from the inside (the Windsurfer comes to mind), almost >> all production boards are created in molds that press the onto the skin >> from the outside. The foam is there largely to support the production >> process.>

Seems to me that the reason an I-beam (or anything like it) is stiffer >> the farther apart the panels (the top and bottom skins of a board) is >> because they are physically tied to each other via the "web." Assuming >> force on the top (gravity is fine, but so is an anvil), the force bends >> the top sheet that would otherwise bend more except for the fact that the >> bottom must take a curve of much greater circumference. This greater >> curve would stretch the material more than it wants to go which in turn >> creates stress within the web in a radial fashion to/from the center of >> pressure coming from above. The greater the distance between top and >> bottom the more the bottom sheet must stretch, therefore the stiffer the >> beam up to the point of failure.>

If this description is correct, then I think it supports my point that >> foam offers little to tie the top and bottom sheets together.>

In the very early 1990's, Seatrend began using "foaming" epoxy that >> managed to squirm its way as fingers between the beads of styrene inside >> their boards. The idea was to reduce delamination, not to increase >> stiffness. Randy French commented that the foam would simply tear apart >> if it carried the bending forces.>

The rails did this, but so did the stringer running from tip to tail. >> I-beam style. Materials do matter. That's why stringers show >> "print-through" over time and why they were incorporated into the foam in >> the first place. The reason composites are used is because they offer >> better strength to weight ratios than a solid substance necessary to >> achieve the same stiffness, and are often much better options to control >> both stiffness and cost at the same time.>>

The rails of the board keep the top and bottom sheet from deforming in >> the same way a cardboard box can support a lot of weight when the weight >> is distributed properly.>

That's my story and I'm sticking to it ­>