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Title: ABYC Maneuvering Test Procedures for Small Craft: Review and Case Studies

Authors: Brian Goodwin and Michael G. Morabito

Abstract: This presentation reviews the American Boat and Yacht Council recommended procedures for turning tests on small, high-speed craft. These inexpensive tests can easily be conducted on existing boats, enabling manufacturers or prospective buyers to evaluate the ability of the boat to turn to avoid obstacles, and also to identify some types of dynamic instabilities that occur during tight turns. To illustrate the use of these tests, two case studies are presented on high-speed, shallow-draft outboard motor boats that have propeller tunnels for reduced draft. The ABYC tests identified two potential problems, the first boat exhibiting a dynamic instability known as "swapping ends" or "spin out" in quick-turn tests, and the second boat failing to turn quickly enough in the obstacle avoidance test.

Physical explanations are provided to describe some of the steering problems with these boats. It is shown that, while there are mitigation strategies that apply for some boats, such as adding skegs to improve directional stability, it is likely that the root cause of the problems is the intermittent ventilation of the outboard motor lower unit, which results in large instantaneous changes in force, taking operators by surprise. The ABYC test procedures, if followed, could allow manufacturers to identify potential problems before boats go into service.