An Investigation of Transom Lift Devices on High Performance Open-Class Sailing Yachts

The principal objective of this research was to determine the merit of transom lift devices on high-performance sailing craft. Transom lift devices modify running trim and also produce several other less-obvious hydrodynamic effects, all of which alter total resistance, thereby affecting the maximum speed achievable under sail. Transom lift devices, in the form of trim tabs, planing wedges, and interceptors, have been used with considerable and quantifiable success for many years on powered craft in both the planing and displacement regimes. This undergraduate thesis extends that research to a round bilged sailing yacht, the Open 60 Imagine—an older Open 60 hull-form by Kaufmann Designs. The effect of transom lift devices was tested on the one-tenth scale model of Imagine in the Robinson Model Basin at Webb Institute. Heel angles of 0, 5, and 10 degrees were investigated at a range of speeds from 1.087 to 13.89 feet per second, model-scale, corresponding to full-scale speeds from 2 to 26 knots. A simplified testing matrix was chosen that did not investigate model yaw, side force, or leeway. Resistance, trim, and sinkage were measured. The study found that transom lift devices, particularly interceptors, greatly affect the trim of the yacht. The devices decrease resistance in the hump region, although on Imagine these decreases were small in magnitude. Importantly, it was shown that the benefits of transom lift devices seem likely to continue even when the yacht is heeled. Outside the hump-region, at both high and low speeds, resistance increased considerably in all configurations. This is thought to be due to increased bow-wetted surface and loss of lift due to excessively decreased trim at the higher speeds. However, it is believed that this study shows that there is considerable merit to the further investigation of transom lift devices on sailing yachts such as Open 60s, particularly more recent hull forms. This paper summarizes work completed for an undergraduate thesis at Webb Institute. Elements of the paper have been designed to meet the original thesis project requirements. Full copies of the original thesis can be obtained from the author or accessed through Webb Institute.