Non destructive testing of boat and rig testing
ELECTRONIC RIG TERMINAL TESTING
Anchor Marine Surveys offers a non destructive (NDT) rig terminal testing service using a Maidsure Meter which can identify the following faults within swaged rigging terminals:
- Internal corrosion within the terminal
- Broken strands
- Cracked terminals in forks and T balls
- Defective swaging
This service is in addition to normal surveys but can be added to a survey at a reduced rate.
THE FACTS ON TERMINAL TESTING OVER REPLACEMENT
Riggers and some insurers will often recommend owners to replace their rigging after ten years and one wonders why? Yes rigging does harden with age and terminals will also age, however the 10 year figure often quoted is an arbitrary figure that has arisen out of clauses in most boat insurance policies that place responsibility on the owner to maintain their yacht in a seaworthy condition and partly encouraged by riggers wanting your work.
Rigging usually fails at the joint between the wire and the terminal for a number of reasons, one common cause is fatigue due to continuous vibration of the wire; another is corrosion at or inside the terminal and also the failure to adequately compress the fitting to the wire during assembly. All of these faults are difficult to detect by visual inspection, so how does an owner provide proof that he has maintained his rig in a seaworthy condition?
BATH TUB CURVE EXPLAINED IN RELATION TO RIGGING
Over many years, and across a wide variety of mechanical and electronic components and systems, people have calculated empirical population failure rates as units age over time and repeatedly obtaining a graph as shown below. Because of the shape of this failure rate graph, it has become widely known as the “Bath tub” curve.
Applying this to rigging terminals the initial region that begins at time zero when a customer first begins to use his boat is characterized by a high but rapidly decreasing failure rate of the terminal. This region is known as the Infant Mortality Period. This decreasing failure rate typically lasts from several weeks to years depending on use.
Next, the failure rate levels off and remains roughly constant for hopefully the majority of the useful life of the rigging. This long period of a level failure rate is known as the Stable Failure Period. Note that most rigs spend most of their lifetime operating in this flat portion of the bath tub curve.
Finally, if standing rigging remains in use long enough, the failure rate begins to increase as materials wear out and degradation failures occur at an ever increasing rate. This is the End Failure Period.
Bath Tub Curve