One of the main differences between rod, wire and fiber rigging (Kavlar, PBO), is the fiber cables susceptibility to damage from environmental conditions. Throughout its life, a section of rod may encounter a wide variety of conditions that really have no effect on its integrity, yet these same conditions could prove detrimental to the life expectancy of fiber cable.
UV and the elements
One example of a damaging situation is a iib sheet or halyard running over a fiber cable. The chafe from this sheet would have no detrimental effect on a section of rod, but could easily wear through the external jacket or internal core fibers. In this case, the fiber is now exposed directly to the elements and can begin to degrade due to exposure to UV light and moisture. Any exposure to either visible or ultraviolet light can cause property degradation, loss in strenght and potential failure of the fibers. Also, high relative humidity at elevated temperatures can cause a loss in fiber strenght oer time. These conditions are common, therefore it is very important to inspect fiber rigging on a regular basis for any damage to the protective jacket, which may expose core fibers.
Inspection of fiber cables is critical for the safe and prolonged use of the cable rigging system. Routine visual inspection of the jacket and its termination points should be frequently carried out in order to maximize the working life of the cable. On passages or during regattas this state-of-the-art rigging technology should be inspected daily.
• Carefully monitoring for signs of damage, abrasion points or breaks in the cover is critical to keep potential damage from UV light or water retention to a minimum. The other inspection point of fiber rigging is at the heat shrink on either end of the cable. Over time there may be a tendency for the heat shrink to pull away from the end fitting or cable slightly. This is normal, and shouldnt pose any immediate problem because it has an inner glue layer that creates a seal between the cable and the heat shrink. Yet, regardless of this glue seal, it should be checked as part of routine visual inspection.
• If your cable system utilizes bi-conic termination technology (socket and cone), it is important to note there is no need to open the socket for internal visual inspection. Unlike rod, there is no head within the socket, and the cone holding the fiber system together is permanently set. Therefore, opening this cable termination will break the factory installed seal designed to protect the internal fibers from the environment.
• However, there are metal fittings attached to these socket as working termination points similar to those used with rod rigging. These fittings should also be routinela inspected as per your normal routine. Things to look for are severe wear, bent pins, corrosion and cracks.
• If your cable system uses continuously wound technology (Z system), it is important to monitor the carbon termination covers for any cracking across the cover or opening at the glue seal. These covers are sealed against the elements, so any breach of the seal will allow UV light and moisture into the termination thus compromising the lifespan of the cable. Also, make sure the cable midspan is checked often for chafe and degradation of the cover.
• One popular fitting that requires more diligent survey and potential replacement is the T-hook. Due to its design, it is typically one of the few fittings with a life expectancy dramatically less than the rod or wire. When inspecting the T-hook, look for cracks on the inside of the sharp bend, as this is a typical spot for fatigue cracking. T-hooks must be diligently monitored and depending on the application (i.e. Kevlar runner) should be replaced approximately once per year depending on usage, mileage and sailing conditions.
PBO Cable Life Expectancy
Based on experience, a PBO cable that has been inspected regularly with no signs of damage can expect following life expectancy depending on the application in which it was used:
• If the maximum working load is less than 25% of the cables rated strenght (lateral or inside rigging – strech application), we recommend changing the as following – 26000-30000 miles or 3 years of use, whichever comes first.
• If the maximum working load is more than 25% (but less than 35%) of the cables rated strenght (headstay or runing backstay – sternght application), we recommend changing the cable as following – 17000-20000 miles or 2 years of use, whichever comes first.
Kevlar cable life expectancy
Based on experience, a Kevlar cable that has been inspected regulary with no signs of damage can expected the following life expectancy:
• If the maximum working load is less than 40% of the cables rated strenght, we recommend changing the cableas following – 26000-30000 miles or 4 to 6 years of use, whichever comes first.