A comparison of experiment and calculated wave-profiles and wave-resistances for a form having parabolic waterlines

Abstract

It has been found possible to calculate the wave-resistance of simple three dimensional forms, and a number of such results have boon obtained which on the whole have shown good agreement with actual measurements when the forms are such as not to violate the assumptions on which the calculations are founded. But the calculation of wave-profiles is at present limited to two dimensional forms having infinite draft. Hence for the purpose of this research two models were made, at the William Froude Laboratory one of the maximum draft possible under mechanical limitations, with vertical sides and a flat bottom, the other having the greatest draft and displacement which would allow of the measurement of its resistance over the desired range of speeds, but with vertical sides for only half its draft and being then rounded oil in vertical section to an edge at the keel. The first model (No. 1254) was used to measure wave-profiles which were compared with those calculated for a model of infinite draft; the second model (No. 1302) was used for the comparison of measured and calculated resistances. It was impossible to use the first model for tins purpose as the added resistance due to eddying round the sharp corners at the bilges would render quite meaningless any calculation of the frictional resistance which must be subtracted from the measured force to bud the wave-resistance. Its wave-resistance was, however, calculated in order to show the similarity in shape between the calculated resistance curves of the two models. Fig. 1 shows perspective sketches of these models and the equations of their surfaces appear below (equations (1) and (7) respectively).