Load / Load
A variety of different factors come into play when it comes to cable life which impact the relative suitability of different fibres and construction methods for each cable type.
(E.g. Verticals, fixed backstays and cruising forestays where the stay is constantly under load)
Testing has shown that under constant tension both PBO and carbon will suffer relatively little fatigue over long periods. As composite rigging technology matures, testing would suggest that it will last a lot longer than steel rod rigging. Cable longevity will actually be limited by the metal in the end terminations which is where a wound fibre construction has a key advantage.
Load/ Off - Load
(E.g. Diagonals and aft rigging)
The important element is going from load to zero or negative load. All materials fatigue faster under compression which is why steel rod diagonals are recommended to be re-headed at 4 years, whilst verticals are considered to be fine for eight. All the fibres suffer the same fatigue mechanism but each material handles it at different rates depending on the fibre's resistance to compression.
Flicking /Bashing
Running aft rigging is subjected to dynamic shock loading and lots of time spent offload/slack. Future Fibres' Enduro PBO aft rigging cables are specifically designed to give them durability against these "cable specific" factors.
Solid carbon is a concern in this application due to its limited flexibility. Modern resins have come a long way and our TSC carbon handles impact extremely well, however, it is still a solid which is being subjected to repeated impact, bending and flexing. A bundle of carbon rods has proven itself to be relatively robust, however, the transition from flexible bundle in the cable to solid resin in the termination creates a natural hinge point on off-load cables and crack propogation in the area is a concern. A Future Fibres dry fibre or FlexC™ cable deliberately has a flexible moulded end to smooth the transition between termination and fibre bundle, to minimize hinging and fibre degradation at this point.
Torsional Loads
Torsional / Code cables require a fundamentally different cable construction to allow the cable to transfer high torsional load whilst retaining flexibility. Uniquely, these cables suffer "packing abuse" i.e. being stuffed into a bag after use. Neither cable UTS or core degradation are the limiting factors in terms of fatigue. In these cables we are trying to control torsional fatigue and the UTS of the torsional layers. The only possible construction is a dry fibre core for these cables.
Coilability
A function of cable length, longer cables need to be practical to handle both on and off the boat. Aft cables and forestays are regularly taken off the boat which favours a dry fibre or FlexC™ construction purely from a practical handling perspective.
Lightning
Carbon is a conductor of electricity, PBO not! Therefore carbon verticals offer lightning a direct/fast route from masthead to water. The affects of a direct strike are unknown but it should be a consideration.
Terminations
As composite technology matures – all fibre cores are offering significant improvements in life over traditional rod. The limiting factor in terms of cable life is increasingly the termination and particularly the use of metal components within the termination. Therefore wound fiber has a long term technical advantage in that it minimizes the amount of metal and the requirement for mechanical transfer of load from the composite material to the mast/boat which increases potential cable life.
Service Recommendations
Future Fibres is pround of its reputation for quality service and support. As pioneers of the composite rigging industry we have had to prove our product at every step along way. As a result, we have an ongoing, active on-the-water testing programme with more logged sea miles under our belt than the competition combined.
Future Fibres has a recommended service programme which has to take into consideration "average use" and splits cables into 3 broad categories: Load/Load, Load/Offload and Running/Torsional cables.
Future Fibres believes these timescales / mileages are sensible periods for cable testing regardless of fibre or construction type. Actual cable life will depend on maximum working loads and extent of "use" (high / average / low), which can be ascertained through cable testing at the timeframes indicated above. Recomendations can then be made on expected further life or any necessary replacements.
