ABSTRACT Two ship motion compensation devices were tested off the coast of Oahu, HI. One device was a traction winch that is capable of maintaining a steady line tension. The other was a ram tensioner. Tests were conducted in various sea states and water depths. Ship and test load motions and lift line tension were measured during the test. The results of the sea test showed that this motion compensating traction winch was not effective in eliminating snap loads. However, the amplitudes of the snap load were reduced by the partial compensation of the winch. The winch had high static friction, which caused a time lag in response to tension changes. The ram tensioner was effective in eliminating snap loads. The maximum tension change in the lift line was less than 30% of the static load. INTRODUCTION The objective of the sea test reported herein was to assess the potential of a motion compensation traction winch as a practical salvage winch for deep sea salvage and recovery. The effectiveness of the winch in preventing snaploads was compared with that of a ram tensioner. Logistic, operation, and maintenance problems were to be identified and documented. After initial unsuccessful attempts to recover an F-14 aircraft off Scotland in 1976 and a 41-foot coastguard boat off Oregon coast in 1977, the Navy's need for a reliable deep depth lift system became apparent. Subsequently, the Naval Civil Engineering Laboratory (NCEL), under the sponsorship of the Naval Sea Systems Command (NAVSEA), devoted considerable effort to the development of a fly-away system that could effectively recover aircraft from the ocean in heavy seas. Through advancements in the analysis of cable dynamics, the resonance behavior of soft lift systems (e.g., nylon line lift system) and the mechanism of snaploads (impact tension in lift lines) are better understood. It is now realized that an increase in the safety factor does not ensure a reliable lift. Cable dynamics analyses are necessary to predict the likelihood of snaploads. If snaploadingis predicted, a catastrophic failure can be avoided by the employment of a ship motion compensation device. A Navy model THR 875A80 ram tensioner has been tested on board Navy workboats in open seas. The results of the sea tests have confirmed that the ram tensioner, which is used to maintain tension in an overhead line of an underway replenishment operation, can provide ship motion compensation to a lift system for various depths, sea states, and payload configurations. The variations in lift line tension were effectively maintained at less than ±20%, thus eliminating any chance of snaploading. Although effective in ship motion compensation, a ram tensioner must operate with a winch which adds to the weight and volume of the whole system - an undesirable characteristic for a fly-away system. Therefore, an attempt was made to develop a single compact and light weight winch unit that would perform as well as the combination of a ram tensioner and a hard Winch.