This paper describes the mechanical behaviour of ropes used for deep sea oceanographic operations. First the requirements of deep sea handling ropes are presented. Two high performance fibres are commonly used, aramid co-polymer and high modulus polyethylene (HMPE), and these are then compared. Results from tests on single fibres and 50 ton break load braided ropes are presented, which show that the initial stiffness of a new HMPE rope increases with load level in a bedding-in process resulting from both molecular alignment and construction reorientation. The aramid rope is less sensitive to this effect and shows a high stiffness from first loading. Measurements made at sea on oceanographic ropes of both materials using an elastic recoil method are presented, and apparent modulus values are consistent with laboratory measurements. Once both ropes have been fully bedded-in the HMPE is significantly stiffer, particularly under dynamic loads. Creep tests indicate that aramids creep less quickly than HMPE under constant loads over a 6 h period at 20 °C. Bending over sheave tests indicate longer lifetimes for the aramid but further tests on wet aramid are required to complete this conclusion. Highlights► Original data on the mechanical behaviour of two types of deep sea handling rope. ► New results from measurements at sea. ► A discussion of the relative merits of aramid and HMPE fibre ropes for this application.

This paper presents first results from a study of the long term marine durability of aramid fibers. The program was started based on the experience of IFREMER using aramid fiber ropes for instrumentation and deep sea handling lines, which is described here. Instrumentation lines showed no degradation after recovery, but results from testing of handling ropes after service indicated significant strength reduction. This led to the development of specific test facilities to study bend-over-sheave performance. The overall aim is to improve understanding of the roles of both the fiber and the rope construction in a marine environment, in order to improve long term strength retention of aramid marine ropes.