Rigging: checking and replacement
This post is also available in: Italiano (Italian)
Today, we will be addressing a very important and delicate topic: we are talking about a real art, that of rigging, which consists, basically, in the discipline that studies, designs and produces the necessary equipment to arm a sailboat, sustaining the mast and making it sail by using the wind as driving force.
For those who sail, well, not a big deal.
It goes without saying, given the extreme and absolute central role taken by the mast-rigging standing on a sailboat, it will be very important to pay the due attention to the maintenance and – when necessary – to replacing the system or part of it.
It won’t be stressed enough that, from the efficiency of rigging doesn’t only depend the possibility to improve our boat’s performances, but also – and much more important – our crew and our own safety.
As many of us will know, today exists essentially three types of cables for rigging: of spiral strand, of steel rod and synthetic. The three types’ performances could be significantly different from each other in terms of aerodynamics, fatigue and stress resistance, deformation and duration over time.
In general, the first question that naturally comes to mind is: how long lasts the rigging? It is not easy to give a unique answer, obviously; in general, we could say that the insurance policy will play an important role in the decisional process on the opportunity to replace the rigging.
On average, insurance companies require the replacement of rigging after ten or twelve years and 20-30.000nm travelled. This figure, crossed with indication of what is covered in case of dismast, could give some points of reflection on when it is necessary to replace the rigging. In case of accident, the insurance company will expect to see proof of maintenance and rigging, and of checks carried out at appropriate intervals by a qualified person; usually, are not accepted self-made inspections.
Coming, instead, to the “practical” side, the main difficulties that ship owners come across when valuing the equipment conditions are the incapacity of seeing the first signs of wear, partially because of the majority of our riggings out of sight, and partially because of the nature itself of the metal’s fatigue.
In a way, it is easier estimate the life of synthetic rigging, since it is provided with a given “mileage” or a given duration if UV rays can damage the material. For those who have steel rigging, the decision of when replacing it can be more difficult.
The fact is that metal fatigue is inevitable. The only thing that will vary is the time taken by a component to collapse. So how can we properly value when to replace the rigging?
There are a few factors that will influence the rigging’s life, particularly the initial quality of the material that you used, and the frequency and mode of navigation.
The rigging quality, whether it is of wire or rod, is important because in both the initial and the growth of the fatigue process phases, it can be accelerated by metallic impurities or by invisible manufacturing defects in the component itself. The use of high quality wire rigging from a respected provider is a greater initial outlay, but the type of metal used and the production process should prolong the rigging’s life.
Buying, instead, a second hand boat, it is important to find out when the former owner replaced the rigging the last time and having a copy of the invoice specifying who was the supplier. In case of uncertainty, you should consult a professional rigger to take a look.
The type of navigation will influence greatly the rigging’s fatigue. In other words, every time that you use your boat, the metal’s fatigue process is advancing, because equipment is subject to the application of cyclic loading. Is it obvious, then, that a boat that sails regularly and “lustily”, it will be getting closer to the point where the rigging’s failure could happen faster than a boat used more occasionally.
Let us bear in mind that a racing boat tends to use a smaller rod relative to the load, to keep both the weight and the wind resistance low. It follows that, during navigation, applied loads are close to the 50% of its breaking load, which will shorten the rig’s life. On the contrary, a cruise boat tends to have a higher safety factor when you choose the rod dimensions, so that loads will be contained between 15 and 25% of the breaking load in maximum sailing conditions.
That doesn’t mean that boats that are occasionally used or used in a “softer” way should never consider the possibility of replacing the standing rigging. Even an inactive boat will be subjected to load cycles in some way when the mast in in place; the wind’s action will be enough on a mast to load the rigging, which, let loose, will move freely with the wind and waves’ action.
To minimize the stress caused by this load cycles during navigation, it is important to adjust regularly the rig so that it is always at optimal tension. This will contribute to guarantee that replacement in load would be less severe. If you are not sure to set the rig’s tension, ask your technician for help and then make sure to check the rig during the whole season.
Talking about rigging’s regular checks, there are a few ways to test the first signs of fatigue, which are undetected to the naked eye; they include colouring agents and NDT (Non-destructive-testing). Both these measurements must be performed with the equipment on the ground and it could be worth it to balance the total cost of carrying out the test with the additional cost you have to bear in case of boat dismasting. Especially, taking into account that if faults or impurities are detected, the insurance may request to replace the riggings anyways. Visual regular checks should detect the first signs cracks growth. Looking for rust on T-shaped profiles and on bent extremities, checking for dusty corrosion at the point where the T-terminals fit into the mast, and eventual signs of cracks in that area itself.
An empirical control method consists in slide your fingers up and down for the last meter of wire above or under the mould, looking for deformities; is the wire is not smooth, then it is probable that one of the wires broke, even if you can see it. In that case, the shroud and its “partner” on the other side must be replaced immediately.
Checking the T-shaped profile is a harder job when they are inside the mast itself. This must be done with the mast removed, it is fundamental, so, to schedule a complete check “mast at land” to be carried out by a professional rigger, at least every three years.
Detecting the first signs of corrosion or replacing components selected after an accurate inspection is a useful exercise since it can prolong the standing rigging and – essential data – can safeguard our safety. Remember that a dismasted boat causes an impact that an insurance claim won’t cover, and that is the human and emotional cost. Those who lived that event can assure it in not a pleasant experience.
Let’s bear in mind that we are always dealing with one of the most devastating factors for metalworking: the wear for fatigue. The wires can break, unseen, inside the profiles. The crack begins when the metal is put in operation for the first time and it is caused by the cyclical loading of metal components.
In case of standing riggings in a sailboat, it is the loading and unloading of shrouds and straws. Think of riggings upwind when they’re put on load while the windward side is relaxed: this cyclical load makes the cellular structure grow inside the metal. These cells harden gradually and so they develop microscopic cracks.
It follows the phase of cracks growth and those microscopic cracks will develop into bigger ones that will eventually be visible at naked eye on the metal component surface. The speed of crack growth phase will vary based on the frequency and strength with which the rigging is subject to load. The final failure will happen when a crack exceeds a certain size that makes the component not tolerate the load anymore. The collapse will be sudden. To overcome this catastrophic event you can use X rays, ultrasounds or other professional monitoring methods.
Once again, we have focused on the necessity of taking great care and paying attention to the maintenance of our boat; once again – and it won’t never be enough – we have seen how our boat requires almost daily checks and periodic attention of expert hands. No getting around, our safety and serenity are at stake. One goes at sea to enjoy the pleasure of sailing and to share this pleasure with people that makes us feel good.
Fair wind, see you at sea.
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