3. Examination
When a side plate of boat is assumed to be of b=600mm with aspect ratio 2, figure 2 shows the result of calculating the thickness of the plate versus the uniform load by the formula (3) for this panel. The condition of the calculation is also assumed k1=0.025, according to requirement of ISO draft for side and bottom plate, that is, w=k1□~b=15mm because of b=600mm. Moreover, it is assumed E=5200N/mm2, in accordance with the FRP material properties of WG18 report (N65) . Figure 2 also shows the values of calculation based on the ISO draft (formula (19)) and those values based on the theory of small deflection respectively as comparison. As shown in figure 2, it is considered that the ISO draft is almost based on the theory of small deflection.
When the pressure is about 20 kN/m2, the required thickness based on the ISO draft is 10mm. This is about 60 percent bigger than the value of thickness based on the theory of large deflection (formula (3)). In case deflection of the plate is 0.5 times or more of the plate thickness, it is recognized to be appropriate that the theory of large deflection shall be applied. As deflection is assumed to be 15 mm, the theory of large deflection shall be applied to the thickness below 30mm.
Further, based on the research of actual FRP boats, their shorter dimensions of the side plate is almost from 500mm to 600mm, then required deflection in accordance with ISO draft(0.025□~b) shall be about 15mm which is the same value of the assumed deflection as above-mentioned.
Consequently we believe that the introduction of the theory of large deflection is reasonably theoretical.
*Note : Our test data of bottom pressure for the boat(Lwl=7.3m) was about 23 kN/m2 at V=29knot.(see Figure 2)
