Wednesday, April 25

Rod Rigging

By Andrew Spaulding, Crowley's Yacht Yard

Rod rigging was invented in the 1970s as a high-strength, low-stretch alternative to wire rigging. As is typical with new products in the marine industry, rod rigging got its start on the race course. Less stretch and weight aloft was the key to rod riggings success. Navtec invented rod rigging and the cold-formed distinctive rod head and continues to lead the world in rod rigging systems. Here at Crowley’s Yacht Yard, we have Navtec factory trained technicians to do our rod heading. We have a Navtec rod heading press on site and regularly service the rod rigging needs of riggers from around the Great Lakes.
When you are ready to consider re-rigging your boat with rod we choose the rod sizes based on equivalent strengths. This will give you the same safety factor that the boat was designed to have. Often, if your goal is to increase the safety factor, we can use the same pin sizes (no changes to the chainplates) and give you stronger rigging.

Typically, the safety factor in rigging is quite high. Most cruising boat have rigging with design loads that are 15% to 25% of the design breaking strength. A race boat might push this ratio to 50%. These safety factors in cruising boats should give the rod rigging a life of about 20 years and yet we are seeing boats go twice that. In my mind this means that boat owners don’t subject their rigging to its design loads. I think this makes sense, since most people don’t pound to windward in 30 knots of wind and 6 foot seas as a matter of choice even though their boats are designed to take it.

Unfortunately for the boat owner this means we can’t really tell when your rod rigging is going to fail. For sure, some day it will fail because failure is merely a function of cycles; meaning that after enough cycles of loading and unloading the rigging it will fail. Whether this happens in 20 years or 40 years is the question that is tough to answer. There are inspections, but without a full disassembly of each fitting and a dye-penetrant test of the rod heads, the inspection isn’t complete. This inspection is a lot of labor (and in some cases requires at least some new fittings since fittings can be peened to permanently lock the threads, this is typical in headstays) and will only tell you that there are no cracks now which doesn’t mean that there won’t be cracks tomorrow.

Since this level of inspection is so labor intensive (read expensive), typically our recommendation after 20 years is to just replace the rigging. To follow manufacture’s recommendations you would to the dye-penetrant inspections as part of a Level C rigging inspection (full service inspection and refurbishment) once every 2 to 4 years in light to ultra-light displacement cruiser/racer to pure racers and once every 4 to 10 years in a mid to heavy displacement cruiser/motor sailor. Unfortunately, most people don’t conduct this level of inspection this often which makes the inspection take longer. Many of you well know that taking apart something that has been together for 20 years is a much different experience than it would be if those parts were together 4 years.

Depending on the results of the inspection the full service refurbishment may include the re-heading of the rod. The rod can be re-headed once in its service life. There is some loss of length when the old rod head is cut off and the new head cold formed. In a continuous rod rig, this is easily remedied by using over-length turnbuckle screws. Using re-headed rod in a discontinuous rig requires rods to be moved to a location in the rigging where the same size rod (but shorter length) is used. For example it is typical in a three spreader rig to move the second diagonal to the third diagonal location after re-heading. In this case, we would have to make a new second diagonal, but we would plan to re-use as much of the rod as possible.

So what does this all mean for you? My personal recommendation is to have your rod or wire rigging (main and genoa roller furling gear also) fully disassembled, cleaned, serviced, lubricated and dye-penetrant test swages and/or rod heads once every 5 years, MINIMUM. For those of you that store your boat inside, taking the mast out of the boat and putting in the storage rack does not count as an Level C rigging inspection. If you stick to this inspection schedule, in most cases your mast rigging system will perform beyond its life expectancy and you will know of any issues long before they cause a problem.

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