- The Japan Society of Naval Architects and Ocean Engineers
- 造船協會論文集 (ISSN:18842062)
- vol.1960, no.108, pp.39-51, 1960 (Released:2009-09-16)
As to the wave-interference phenomena connected with the bulb there have been presented two kinds of explanations : one being theoretical, and the other practical.Following the theoretical explanation, which is largely indebted to Havelock and Wigley, we may assume that the wave-making characterististics of the bulbous bow can be safely represented by an isolated point doublet. If admitted, this goes at once to the conclusion that the free wave patterns due to the fitted bulb can be intentionally put just in inverse phase or with strictly half wave-length difference against the main hull waves. This is nothing but the most desirable situation for us in view of promoting the maximum interfering merits of the bulb.On the contrary, the other explanation enforces, rather practically, too much importance of the virtual increment in the wave-making length of the hull which is caused by the bulb waves. In this way, it has long been believed that the reduced wave-making resistance accompanying the bulbous bow has much to do with its increased “effective wave-making length”. From this standpoint of view, it is suggested that, when any amount of bulb merit observed, the bulb waves must proceed by some intermediate fraction between 1/41/2 of ship wave length against the main hull waves. This means that from the bulbous bow we can expect only an incomplete interfering merit at the best.This report is aimed for the experimental determination of the existing conflict, mentioned above, with regard to the 'actual' phase-difference between the bulb waves and the hull waves. The wave analysis procedure is applied for the first time. The conclusion is that the theoretical treatment of the bulb which is introduced by Havelock and Wigley can be practically approved. A few remarks are also made on the two different phases of the hydrodynamical characteristics of the bulbous bow. Its corresponding system of singularities is represented by the combination of an isolated doublet with a continuous source distribution.The former has a positive and therefore the same sense with the latter in hull form characteristics, but has a negative and therefore the reverse sense in wave-making characteristics. This is the true reason why the wavemaking resistance is sometimes reduced remarkably with the bulbous form whose displacement is larger by its bulb than the original form.