The U.S. Navy has been investigating the viability of a combined bow bulb and sonar dome concept on a combatant hull. A new type of near-surface, small volume, hydrodynamic bow bulb was developed, and integrated into the existing combatant bow which houses a sonar dome. Substantial resistance reduction was demonstrated through initial calm water model tests, which defined parameters for bow bulb volume and longitudinal position. An investigation was then undertaken to quantify the effectiveness of the near-surface bow bulb concept in irregular waves. The goal was to improve the bulb design so that the calm water resistance reduction was retained through rough water of sea states 2 and 4. The bow bulb was evaluated with variations in bulb height, breadth, cross-sectional shape, and depth of submergence, while retaining equivalent bulb volume and longitudinal position.

Through several design refinements, a small volume, near-surface bow bulb was developed that significantly reduced resistance in calm water, and retained an equivalent resistance reduction in sea states 2 through 4, Figure 1. The selected bulb had a substantial performance improvement compared to the baseline (no bulb) configuration, in calm water and rough water, throughout most of the speed range. One of the energy enhancing characteristics of this bulb design was its effectiveness at reducing resistance at all ship speeds, even as low as 5 knots, in both calm and rough seas.

Some guidance is also offered as to bow bulb design compromises necessitated in order to balance both calm water and rough water bulb effectiveness. Bulb cross­sectional shape appeared to have less of an influence on bulb performance than the vertical positioning.

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