Investigations on Model-Shio Correlation of Small FRP Fishing Boats

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  • 小型 FRP 漁船船型の模型と実船との相関に関する一考察
  • コガタ FRP ギョセン センケイ ノ モケイ ト ジッセン ト ノ ソウカン

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Abstract

Small FRP fishing boats have recently been built extensively and most of them have hull forms of high speed type with hard chine. In order to clarify scale effect on this type of boats, FRP Hull Form Development Committee carried out full-scale and model tests for two fishing boats. This paper deals with the test results and their analysis. Two actual boats tested are Nikko-maru and Koshin-maru. Both of them are 11m FRP fishing boats with hard chine. Nikko-maru has skegs and Koshin-maru has not. For two actual ships, 2.9 m wooden model ship and corresponding model propellers were manufactured. Model tests were performed in No.2 Tank of the Shipbuilding Research Centre of Japan. Principal results obtained from the above tests are as follows ; (1) Although scale ratio of the models to the actual boats is only about 1/4, values of wake fraction are a little different between the actual boat and the model. (2) Roughness allowance ΔC_F obtained on a base of Schoenherr's method is quite large and decreases with the increase of ship speed. (3) Expressing resistance argumentation due to wind and wave by ΔC_F', ΔC_F'≒1.7×10^<-3>. This value was obtained from the full scale experiment of Nikko-maru in waves and Koshin-maru is calm sea. Therefore, some other effects than wind and waves may be included in this value. (4) If there is no scale effect on wake fraction, ΔC_F based on Schoenherr's friction line will be about 1.2×10^<-3>. (5) The total resistance coefficient of the actual ships, which were obtained assuming that thrust deduction coefficient does not vary between the ship and model, crosses with that of the models at Fn≒0.88, and is higher at the lower Fn. (6) Running trim is nearly the same between the ship and model.

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