Attaching Synthetic Standing Rigging to Your Mast

Synthetic standing rigging sounds amazing. It’s lighter, stronger, and easier to install than steel rigging; but how do you attach these stays to your mast?

Steel rigging ends in a compression fitting or swage fittings which grips the end of the cable and attaches it to the mast. Synthetic stays can’t be squeezed into a swage fitting or pinched by compression fittings. So how do you attach your new synthetic stay to the spar?

Easy! Instead of a compression type fitting that grips the bitter end of the stay, all you need to do is create an eye splice into the end of the stay. The eye splice simply slips over the clevis pin and attaches to the stay to the spar!

While steel rigging ends in fancy mechanical fittings that need to be purchased, synthetic standing rigging ends in an eye splice which is easy to do yourself!

Synthetic rigging is very easy to make and very easy to install.

Thermal Expansion and Rigging Tension

Thermal Expansion is the phenomenon where objects become bigger as temperature changes. In general, with most objects in the world, as things heat up, they also expand. Negative Thermal Expansion is reserved for those rare occasions where materials actually contract as they heat up; Dyneema is one such material.

On a yacht, the rigging must be perfectly tuned to hold the mast in column while withstanding the forces of the wind placed upon the sails and spars. This perfect tune revolves around the lengths of both the spar and the standing rigging. If one of them were to change drastically, so would the tune!

Unfortunately, all materials used in rigging have slightly different coefficients of thermal expansion. Where thermal expansion was the phenomenon of changing size, the coefficient is the rate of such change.

The issue comes down to mixing materials for the spar and standing rigging that will be changing size at various rates.

The most common spar material at the moment: Aluminum, has a coefficient of 23.1 x 10^-6 per Kelvin (or for practical applications “per *C"). This is to say that 1 meter (39 inches) of aluminum will expand or contract 0.000023m for every degree change in Celsius. This might not sound like much, but if you think about a yacht that will endure summers and winters, the temperature change can be rather drastic.

Imagine a yacht that sails in temperatures from cold winter days of 0*C all the way up to hot summer days of 40*C. That is suddenly a 40 K change (Each degree of Celsius is equivalent to 1 Kelvin). On a mast that is 19m tall (62 feet), that means that the change in length of the mast will be:

( 23.1 x 10^-6 / K ) ( 19 m ) ( 40 K ) = 0.017556 m = 17.56 mm ( 0.69 inches )
That is a pretty drastic change in size of your mast!

The next material to think about for a spar is wood, and while Sitka Spruce is the ideal wood for a spar, it is becoming ever harder to find good clear wood for the purpose. The next best wood for a spar, and the one that is becoming ever more popular as a wooden spar is Douglas Fir with it’s coefficient of 3.5 x 10^-6 per Kelvin (when parallel to the grain). The same spar now becomes:

( 3.5 x 10^-6 / K) ( 19 m ) ( 40 K ) = 0.00266 m = 2.66 mm ( 0.10 inches )
Significantly less change in length.

The last common spar material these days is also a very modern material: Carbon Fiber (Carbon Fiber Reinforced Polymers) with a coefficient of -0.8 x 10^-6 per Kelvin. The negative is an important part in this because that means that as the carbon fiber spar heats up, it also contracts!

( -0.8 x 10^-6 / K ) ( 19 m ) ( 40 K ) = -0.000608 m = -0.608 mm ( -0.024 inches )
This material is incredibly stable and barely changes size during the whole year, with its longest being on the coldest days and the shortest on the hottest of hot days, but the difference is less than 1 mm!

A changing spar length means very little if this change is not relative to something else, something like your standing rigging!

The most common material for standing rigging is Stainless Steel with a coefficient of 16.5 x 10^-6. Grade 304 and 316 both have the same coefficient which is why you don’t have to worry about which type is being used in your rigging.

On a spar that is 19 m tall, the cap shrouds will be roughly about 20m long (the beam of the boat is the only additional length in the stay, and this is run at an angle). Lets see how much the length will change over the same temperature variation:

( 16.5 x 10^-6 / K ) ( 20 m ) ( 40 K ) = 0.01254 m = 12.54 mm ( 0.49 inches )

This means that the steel rigging will expand almost half an inch over the years temperatures.

When you combine an aluminum spar with steel rigging, the variation is about 17.5 mm while the rigging is about 12.5 mm. This means that they will expand and contract together and only at the extremes be off by a few millimeters.

On a wooden spar with steel rigging, the difference would be 2.66 mm for the spar and 12.5 mm for the rigging. This means that on the really hot days, the rigging will be about 1 cm longer than the spar if the rigging was setup on the coldest of days.

On a carbon spar with steel rigging, the difference is a bit more drastic. The spar will contract by 0.6 mm while the rigging will expand by 12.5 mm. This means that if the rigging were tuned on the coldest of days, the rigging would be 1.25 cm too long on the hottest of days. If a boat has a carbon spar, then you can assume that the owner of the yacht is interested in performance and therefore would notice the horrible state of the slack rigging!

A newer material for standing rigging is UHMWPE, or Dyneema. This plastic fiber has a coefficient of linear thermal expansion of -12 x 10^-6 per Kelvin. Just like with the Carbon Spar, Dyneema also contracts as it heats up and expands as it cools.

( -12 x 10^-6 / K ) ( 20 m ) ( 40 K ) = -0.00912 m = -9.12 mm ( -0.35 inches )
The change in rigging length is rather dramatic, very close to the change in length of stainless steel rigging, except in the opposite direction. As steel expands, Dyneema contracts and as steel contracts, Dyneema expands.

When we pair these with spars, we see a rather drastic difference emerge!

With an aluminum spar: 17.56 mm expansion of spar and 9.12 mm contraction of rigging as it heats. This means that the difference between the two will be 26.68 mm ( 1.05 inches ) of difference!

With a wooden spar: 2.66 mm of expansion of spar and 9.12 mm contraction of rigging as it heats, with a difference of 11.78 mm ( 0.46 inches ).

With a carbon spar: 0.61 mm of contraction of spar and 9.12 mm contraction of rigging as it heats, with a difference of 8.51 mm ( 0.33 inches ) but going in the same direction.

The take away message here is that the components of your standing rigging will change as temperatures fluctuate. Some materials do not change much while other materials change drastically! Knowing which material combinations you have is imperative to properly setting up your rigging and having it perform the best that it can under most conditions.

If you fail to take into account the temperature fluctuations, you risk serious damage to your yacht. Think about it, if Dyneema rigging on an aluminum spar have almost a full inch of variance between the two, if you setup your rigging on a cold day everything will become too tight during the rest of the year! As spring comes, the mast will get longer and the rigging will get shorter. By summer, your chainplates will rip through your deck or the tangs on your mast will crack!

To prevent such a catastrophe, you simply need to take this change in length into consideration and setup your rigging on a hot day. Not necessarily the hottest day, but a hot day none the less. As winter approaches, your rigging will go slack and no damage will befall your yacht. If you wish to sail in these conditions, you will need to adjust your rigging, and then adjust it back in case you don’t revisit your yacht before a warm day appears.

If you have an aluminum spar and steel rigging, the two materials change length in the same direction and almost at the same rate, this means that you probably will never notice any issues with temperature affecting your rig tune.

If you have a carbon spar, you should have Dyneema rigging for the exact same reason as an aluminum spar and steel rigging. The change will be in the same direction and roughly the same rate so that the temperature range of proper tune can be wider than it ever could be on an aluminum spar.

Covering the Standing Rigging with PVC Pipe

Chafe is a terrible thing for your rigging. The constant sawing action of two pieces rubbing together will damage one or both of these components which can lead to costly repairs or serious equipment failures!

A simple solution to protect your standing rigging is to cover your stays with PVC pipe. The stay can be covered with a small diameter pipe while the turnbuckles can be covered with a larger diameter pipe. Now everything is smooth and protected by a sacrificial layer of plastic. Nothing to rub on and nothing to snag!

The truth is, covering your standing rigging is actually a very bad idea. First for the structural integrity of your rigging, and second for the fact that “out of sight out of mind” is a dangerous motto on a sailboat.

The reason stainless steel is “stain less” is because the it contains more chromium than regular steel. The chromium reacts with oxygen to form a protective layer over the metal and prevent it from corrosion. In the absence of oxygen, this protective layer does not form and crevice corrosion can begin to occur.

Crevice corrosion is a very hard to see kind of corrosion that looks like little cracks in the steels surface. These microscopic cracks run deep beneath the steels surface and actually cause the steel to split and break apart. Crevice corrosion is a major reason why steel standing rigging only lasts about 10 years, longer than that and the rigging will be at too high a risk of having microscopic crevice corrosion which will cause its demise.

Creating a sealed environment will create an environment where the oxygen gets used up until it becomes oxygen deprived and crevice corrosion will begin. This means that the rigging will die earlier and sooner than if it were left exposed to the elements; and more importantly exposed to oxygen.

The other problem with covering your rigging is that you don’t see it. Minor issues like “a pin fell out” or “that looks rusty” will go unnoticed because they are not easily seen. Every boat owner has good intentions to properly care for their boat, but when you walk down the pier at any marina you will see the effects of chronic neglect! Covering your rigging will create one additional step in the process of inspecting your rigging, and that is a process that sadly is usually relegated to “if it catches your eye” inspections.

By having your rigging exposed, you will see it and you will hopefully look at it and if anything changes on it you will notice it and fix it before the problem escalates out of control and your mast comes down!

So, while covering your rigging makes it looks sleeker, it is best to avoid all the work involved in covering your rigging and keep it visible. This will make it last longer and make it easier to inspect so that your entire yacht will continue to perform at its best.

Dyneema and its Coefficient of Thermal Expansion

Dyneema, while being incredibly strong, light, unaffected by water, and UV resistant, it is still a material of this mortal world. As such, it has various physical properties that can not be ignored.

One of these physical properties that can not be overlooked is the way Dyneema will change in length as it heats or cools. Sure, all normal materials experience this phenomenon, so what makes Dyneema special?

If you look at a bridge, you will see those nifty expansion joints in the roadway. These allow the bridge to expand and contract without breaking the bridge. If you look at these joints during the hot days of the summer, you will notice how the finger joints are fully interdigitated. Yet, in the winter on a very cold day, the finger joints will be pulled apart.

Concrete behaves as most materials do, expanding as they heat up and contracting as they cool down.

This expansion and contraction actually happens at a fixed rate that is known (by experimentation) for each material. The rate is called the Coefficient of Thermal Expansion and for all things that expand when they heat, this coefficient is a Positive Number.

Dyneema is a special material because it actually behaves backwards to this common convention. It will contract as it heats and expand as it cools, resulting in a Negative Coefficient of Thermal Expansion. This rare trait means that it will change length on you throughout the year and probably in an opposite direction to everything else on your boat.

In the summer, as your mast grows slightly longer, your stays will become slightly shorter. In the winter as your mast grows ever shorter your stays will become even longer!

Dyneema has a Coefficient of Thermal Expansion of -12 x 10^-6 m / K. This means that for every change temperature equivalent to 1 Kelvin (also equivalent to 1 degree Celsius) a meter of Dyneema will change its length by 0.000012 m, or 12 μm.

A little more clearly, for every degree change in Celsius, Dyneema will expand or contract by 12μm for every meter of length of the line.

This might not sound like much, but the temperature fluctuations throughout the year on a yacht can easily be 40 Kelvin (or 40*C) and stays on a yacht are very long. Each meter of Dyneema is now fluctuating by 480μm. That’s almost half a millimeter per meter!

This all adds up and in the dead of winter, your rigging can be significantly longer than you expected and thus very slack, or by inverse it could be very tight as it contracts on hot days.

Being how Dyneema expands as it cools and contracts as it warms, it is imperative to always tune your rigging on a warm day that way, worst case, your rigging is a little loose. If you tune your rigging to perfection on a frigid day, by Spring your rigging will have contracted so much that it will break something else on your yacht. Let’s face it, the synthetic standing rigging is going to be the strongest part of your rigging so something else is going to break when the stays all contract!

By being mindful of this physical property, you can safely enjoy the ease of inspection and reduced weight aloft that come with synthetic standing rigging.

Looking at Wire Rigging

I know I focus a lot on Synthetic Standing Rigging on this blog, but there is one important point to make about all rigging: They work until they fail.

Replacing steel standing rigging to synthetic standing rigging is a waste of money. Rigging is expensive and while synthetic standing rigging is cheaper than steel standing rigging, the cheapest standing rigging is the one you already have!

This is why I feel it is important to know how to look at your steel standing rigging to better determine when it needs replacing. Once your rigging needs replacing, that is when deciding what material to go with makes monetary sense!

This is what your standard 1x19 Stainless Steel wire (304, 316, or 316L) should look like. All the strands are pretty, polished, and clean. There are no signs of corrosion or other problems with the wire. Dirt is a fact of life and should not be a cause for alarm. Some boat owners go above and beyond to keep dirt out of every surface of their yachts; and while this is a positive trait in someone selling you a boat, it is also not practical or realistic to keep every inch of wire on a sailboat clean and free of dirt or debris!

Now we start to see problems develop. This wire is still in adequate condition for now, but its end is approaching. This is when you should begin saving up for the cost of replacing your rigging and deciding what material you wish to replace your standing rigging with!

Are you going to replace your rigging yourself or are you going to pay a rigger to do it? If you are going to pay someone, will they come to your boat or do you need to take your boat to the yard where they work? This would also be a good time to start collecting estimates from different riggers that way you know where you will be going when the end of the line finally comes.

When your rigging looks like this, you can still sail on it, but you need to keep a close eye on your rigging because it is dying. It is not dead yet, but it will be getting there!

This is what wire looks like when it is on its last leg. You can see many spots where rust is occurring. The strands have lost their luster and appear dull and tarnished. Rust spots are less the rare occurrence and more the norm, as almost each visible strand has multiple rust spots on it.

It is important to note the strict difference between rust staining and rusting metal. If you take perfectly fine stainless steel and rest it up against a rusting piece of metal, the iron oxide from the rusting metal will stain your perfectly fine stainless steel. This means that if you have a low quality piece of metal attached to your rigging and it begins to rust, the metal of the stay near this will develop a rust color. Rust stains polish off and the wire will go back to looking like new.

If the wire itself is rusting, there is no amount of polishing that can be done to remove all the rust and restore the original luster of the wire. When the stay itself is rusting, that is when it is at the end of its lifespan.

When the stay begins to corrode like this, it should be replaced promptly. Yes, you can still sail in light conditions with it as it has now “failed” yet, but it will soon fail and should be replaced.

Failed rigging is when it actually breaks, and while you can sail with your rigging until that occurs, the problem is that when a failure occurs during use, the repairs tend to be rather costly!

Imagine for a moment that you have your sailboat sitting in the slip and the port cap shroud begins to develop significant corrosion. At this point, your sailboat is sitting in the slip with the mast standing straight and tall. Nothing has broken or given way yet.

You make arrangements and either replace the stay yourself or hire a rigger to replace the stay for you. Then you go sailing with your new stay and nothing happens.

Now lets imagine the same situation but instead of replacing the stay when it was dying, you wait for the stay to fully die. You are sailing along on a close reach on starboard tack. The spray is coming over the bow and you are heeling well to leeward. Everything is wonderful and then you tack. Now all that load is on the corroding port cap shroud and the failing stay finally fails. The wires break and the mast becomes unsupported. The cap shroud had broken and the only think holding the mast up in the air are the lower shrouds! The force of the wind on the main and headsail pull harshly against the top of the mast which is no longer being supported by the port cap shroud and the mast begins to bend. The mast bends further and further causing the sails to become baggy and hold even more wind, and pulling even harder on the unsupported mast until it buckles at the lower spreader attachment.

Now you have a broken mast as well as a failed port cap shroud!

This is why you want to replace your stays when they are failing instead of waiting for them to fail.