Wow.

Have you reached any conclusions yet about your own layup? Please keep us in the loop if you do.

: I have read Open Water Kayak’s “Standard Engineering Model” and have some
: questions. I have attempted to cross reference the concepts with E.P.
: Popov’s Mechanics of Materials..

: (Smax I)/
: ((Tw+Tg)/2)

: Popov calls this the “Flexure Formula”;

: ((Tw+Tg)3 - Tw3) + Tw3(Ew/Eg) /12

: Popov describes this formula for moment of inertia as “transformation of a
: section”.

: (M2 L )/
: (2 I Eg)

: This formula is the maximum amount of strain energy a cantilevered beam can
: store without failing.

: 98/12

: The density of glass is needed to determine the thickness of the glass
: portion of the composite.

: 22/12

: The density of wood is needed to determine the weight of the wood portion of
: the composite.

: (WPw W)/Dw

: The thickness of the wood is needed to calculate moment of inertia.

: ((1-WPw) W)/Dg

: The thickness of the glass is needed to calculate moment of inertia.

: 600*Tg

: Where is this used?

: .05 Eg = Ew

: This is used in the transformation method of computing the composite section
: moment of inertia.

: (((Tw+Tg)3 - Tw3) + Tw3(Ew/Eg)) Eg /12

: This is the moment of inetia times the modulus of glass, as described in
: Popov’s transformation of sections.

: 18W3Eg (1331+13794WPw+47652WPw2-(62777 +117649Ew/Eg)WPw3 ) /156590819

: I tried to expand the equations above and did not come up with this result.
: Can you show some intermediate steps?

: In the above equation, the static strength does appear to vary according to
: the square of the weight, when wood as a % of weight is constant.

: In the above equation, the static strength does appear to vary according to
: the tensile strength, when wood as a % of weight is constant.

: Then, fixing all variables except the wood as a % of weight you found a curve
: with a peak at .63%. I used the calculation for the moment of inetia times
: the modulus of glass, as above before the substitutions to calculate the
: curve as a check. Keeping W constant and keeping the wood as a percent of
: weight constant, the curve did not have a peak. Similarly, the static and
: dynamic curves did not peak. Should I have seen a peak using equations for
: before the substitutions were made?

: Your dimensional analysis approach is very intriguing, and would be very
: useful provided it is understood. I am ready to start fiberglassing, and
: this discussion has already given me a lot to consider.

: Thanks in advance for any help you can give. I like many others am very
: grateful for the level of commitment and effort that the builders on this
: site have for helping us novices.

: Tom