A tensioner for deploying a member such as a pipe or cable, such as a sub-sea cable deployed from a ship, comprises an endless track and drive means for driving the track. The track includes a plurality of traction elements mounted thereon for movement with the track. Each traction element includes one or more cushions for supporting the member, and a pair of opposed arms mounted on respective sides of the base of the traction element. One or more of the arms is pivotally mounted for movement between a clamping position and a release position. In an alternative arrangement, four moveable arms are linked in diametrically opposite pairs to move between a release position and a clamping position. Cushions on the arms clamp the member in conjunction with the cushions of the traction element, when the arms are in the clamping position. Guide means are provided to urge the arms into the clamping position to grip the member as it passes through the tensioner.