Surging motions of a towed undersea cable plow

Any section of undersea cable that can be struck by objects scraping the sea floor must be protected. It is often placed in a trench for protection. Towing a plow from a surface ship is the most economical method to dig the trench. Cable is passed through the plow and into the trench as it is plowed. It is the current practice to bury armored cables at slow speeds. There are economic advantages to plowing unarmored cables, at higher speed, but unarmored cable is more difficult to bury because it has low weight. It is shown that tension pulls such cable out of the trench in undulating terrain. This establishes the need for a cable engine on the plow to reduce cable tension in the trench. To keep trench tensions low the cable engine must track the velocity of the plow. A simulation has been developed to establish bounds on the plow velocity excursions during steady state operation. These results will be used in the design of a cable engine, and its control system.