Over 45 feet the results are adequate and closer to the 60 foot size real gains are being achieved. It is possible that the stocky hull form commonly used is not compatible with the characteristics that make the bulb work. Possibly, development of a new hull form may be required in vessels under 45 feet to benefit fully. Motorsailers have also been known to indulge in the bulge. So much work has been done with various configurations, shapes, and sizes, that an average bulb can be designed for displacement vessels with fairly predictable results.
Detailed information is required about the vessel's hull form, area of midsection, etc.
The more accurate the information, the better the results. For maximum benefit model testing is still required to fine tune the proportions to the hull form. It is also an opportunity to preview the results before the work is preformed on the full size vessel. The greatest amount of benefit will be at the high end of the displacement speed range, reducing as your speed decreases. At higher speeds wave making resistance accounts for the greater portion of the drag, and the slower you go proportionally more of the resistance is taken up by wetted surface drag.