Advantages of Running Model Tank Tests with the Client Present

During April 1998, tests were run in the Webb Model Basin on a 1/12 scale model of a fast trawler type motorboat designed by Bruce King for Pacific Seacraft. The tests involved measurements of resistance, heave and trim at the design displacement and two others over a range of speeds of the hull and CG as designed. The test matrix was planned to take one test day (approximately 40 runs). The client (designer) was to be present. The model scale was 12. The design speed was in the neighborhood of 25 knots and the design displacement 25000 pounds, putting the craft definitely in the planning hull range. The craft lines are given in Figure 3 and show a moderate Vee bow with a chine and flat run in the stern. The model, as designed, was tested in the morning at the design displacement and center of gravity over a speed range of 12 to 30 knots. The results are shown in Figure 1 (solid lines with symbols) and the data is given in Table 1. It was apparent, visually and in looking at the data, especially the trim that was almost 7 degrees in the planing range over 18 knots, that the craft needed some redesign. Also, the resistance was correspondingly somewhat excessive, over 12 percent of the weight. We needed to get the trim down to 5 degrees, known to be ideal for planning conditions. Rather than continuing the test series at the other displacements, the team, including the designer, broke for an early lunch to discuss the situation. Normally, there would ensue a test report prepared and mailed showing the trouble, the model returned for changes, and another test day planned to hopefully complete the study*. But, we were all together, including the designer, and had lots of waterproof tapes, modeling clay, and strips of sheet aluminum available to adjust the stern lines. So, we went to the tank and back to work!