Abstract: A method of coating a pipeline comprising the steps of:Welding joints of pipe, end to end to form a continuous pipeline having an entry end and an exit end, winding said pipeline onto a reel, and coating the interior thereof by inserting a pig into the pipeline at one end thereof and affixing a cap at the other end thereof, introducing a coating liquid into the pipeline on the reel, and rotating the pipeline while the pig is maintained in a relatively static position so that the pig smoothly and evenly coats the pipeline as it rotates.

Abstract: An underwater trenching machine comprising a carriage and a pair each of fore and aft pivotal frames, each of which carries a drive roller means for intimately contacting the pipeline, said front and rear frames being adapted to mutually exclusively pivot outwardly upon command so that the frame carrying the roller means resting at that time on the pipeline takes over the drive function performed by the roller means on both pair of frame means theretofore, and further including improved jet legs each divided into multiple sections for enabling differential water velocity while minimizing water pressure loss through the length thereof, all while the machine is maintained at a predetermined buoyance and attitude.