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Old 05-17-2017, 11:08 PM   #10
GoneFarrell
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City: La Conner, WA
Country: United States
Vessel Name: Imagine
Vessel Model: Farrell 34
Join Date: Oct 2015
Posts: 269
Simi,
I can explain it with a formula that has served me and my customers for over 30 years: I=B*H^3/12.

The FRP skin you reference is on the outer fibers of the "beam" and that is a cubic with distance from the neutral axis effect. So the FRP far from the neutral axis does a great job of adding stiffness. As does the outer strip planking, which is stiffer than UHMW, it is efficiently used because it is far from the neutral axis.

With a simple UHMW beam, there is no stiff material far from the neutral axis, hence it cannot be as stiff and strong.
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