Self-lubricating ropes useful in the isolation sections of ocean-bottom cables
View Patent ↗A rope having an outer jacket made of braided fibers surrounding a PTFE core and a method for making the rope. The rope is useful in high-tension, high-friction applications, such as serving as a stress member in an isolation section of an instrumented ocean-bottom cable. The PTFE core, which may consist of one or more strings of PTFE valve packing material, squeezes through the braided jacket as the rope is deformed in high-stress regions such as around a bollard. The PTFE material squeezed through the outer jacket lubricates the outside of the rope in the high-stress region to lower the friction.
1. A stress-member rope for use in an ocean-bottom cable isolation section, the rope comprising:
fiber strands made of a high tensile strength material devoid of PTFE and braided to form an outer jacket surrounding a hollow interior core; and
a PTFE string residing in the hollow interior core.
2. A stress-member rope as in claim 1 wherein the outer jacket is made of DYNEEMA® fibers.
3. A stress-member rope as in claim 1 wherein the PTFE string extends the length of the rope.
4. A stress-member rope as in claim 1 wherein the PTFE string makes more than one pass through the hollow interior core.
5. A stress-member rope as in claim 1 wherein the PTFE string fills the hollow interior core sufficiently so that tension in the rope that causes the rope to deform and the hollow interior core to shrink at a rubbing position along the rope's length forces material from the PTFE string in the hollow interior core through spaces between the braided strands in the outer jacket to lubricate the rope at the rubbing position.
6. An isolation section of an ocean-bottom cable, comprising:
a first connector having bollards on its periphery;
a second connector spaced apart from the first connector and having bollards on its periphery;
a rope having loops at opposite ends looped around first and second bollards on the periphery of the first connector, the rope running back and forth between the first connector and the second connector and guided around other of the bollards on the peripheries of the first and second connectors;
wherein the rope includes a braided outer jacket of multiple strands made of a high tensile strength material devoid of PTFE surrounding a hollow interior core and a string of PTFE material residing in the hollow interior core.
7. An isolation section as in claim 6 wherein the amount of PTFE material in the hollow interior core is sufficient so that tension causing the rope to deform and the hollow interior core to shrink at the bollards forces the PTFE material in the string from the core through spaces between the braided strands in the outer jacket to lubricate the rope at the bollards.
8. An isolation section as in claim 6 wherein the string of PTFE material extends the length of the rope.