Rig Testing

Should you replace your rigging after 10 years or not?

Well, there is not a definitive answer to this question as the 10 year figure 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?

One option favoured by riggers is to renew the entire rigging! Unfortunately this could increase the risk of rig failure as all manufactured items go through an Early Failure Period, Stable Failure Period and End failure Period often known as the Bathtub curve. The time for an item to reach these various periods in its life varies according to use and subsequent wear and cannot be pigeon holed by age, in any case, what’s to say the old rigging wasn’t in its Stable Failure Period which has less risk of failure then the Early Failure Period on the new rigging.

The second option which doesn’t use arbitrary age periods is to have the terminals on your rig tested with a Non Destructive Test (NDT) using a sensitive Ohms meter using the four wire Kelvin method of measurement. This measures the very low resistance across the neck and body of the terminal which is compared against a table of known readings for a terminal of a similar size and will identify any degradation or weaknesses within the terminal. This same system has been used successfully by the electricity supply industry for over 18 years to test the terminals on overhead power lines.

The test is a comparative test so it is best to have the terminals checked at regular intervals. Ideally every new boat or recently re-rigged vessel should have the terminals checked to provide a datum point from which to compare against future readings but also to identify terminals that were poorly assembled or swaged from the onset (Early Failure Period). The time between further terminal checks will vary according to use. For example, if you only cruise around the Solent in fair weather a check every five years should satisfy an insurance company that you are making the necessary checks to maintain your rig in serviceable condition. Alternatively if the boat is used commercially, raced or the rigging is nearing its end failure period then a two year check would be more appropriate.

One advantage of NDT testing is cost. Rather than paying thousands to replace the vessel’s entire standing rigging, you only replace the wire and terminals that are showing signs of failure. The terminals can be NDT tested while the boat is afloat; however the cost of the test is dependent on the ease of access to the terminals. A typical 30ft vessel would cost in the region of £135 while afloat but just £80 when the rig is down.

Article by Tim Barker – Anchor Marine Surveys – 02392 469240
Northney Marina, Northney Road, Hayling Island, Hants. PO11 0NH

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