How much chafe is too much?

Dyneema is a wonderful synthetic fiber that is lighter and stronger than comparably sized steel. While its strength is unmatched, chafe is its weakness. But how much chafe can the stay withstand? When is it considered a structural concern?

The only way to accurately determine how much strength is left in the line is to perform a destructive pull test, which destroys the line. A study was performed by Samson to determine if there was a correlation between visual cues and residual strength left in the line.

Abrasion, or chafe, lead to broken filaments in the line spread out over a large area of the line. This will result in a fuzzy appearance to the line which will be our visual cue as to how damaged the line is and what the estimated remaining residual strength is.

The visual scale runs from 1 to 7, 1 being minimal damage and 7 being severely damaged.

Source: http://samsonrope.com/PublishingImages/Currents/July%202014/04C_Pocket_Guide_Image.jpg

The general guidelines are:

1 and 2, safe to continue using
3, 4, and 5, consult and expert
6 and 7, retire the line

External wear is caused by chafe, over loading, and UV damage. Internal wear is caused by passing the line through repeated severe bends and introduction to rough substrate, such as working the line through gravel. 

Internal damage is more likely to occur in other uses, such as pulling a log through a forest, where the line is dragged along the dirt forest floor. 

In the world of standing rigging, internal damage is not such a concern. The stays are fed through thimbles to ensure that they have proper radius bends, and they are not worked through the bends regularly. It is a one time thing and then they are set for life. The rigging won't be exposed to gravel, but I haven't found any information about salt crystal exposure. Regardless, there is minimal movement in the stay, so internal abrasion should be a minimal occurrence.

External wear is a concern though. The outer fibers will be exposed to UV, which will cause some degradation, but they will protect and shield the internal fibers from further UV damage. This will eventually lead to a fuzzy layer around the whole stay, placing it in category 1 or 2, thus still safe to use. Since this damage is minimal, I don't recommend using a sun cover, as it would add bulk and windage.

As far as chafe goes, all damage will be located on the outer layer of the fibers and usually only on specific areas where the chafing occurs. When these areas begin to show up as a localized fuzziness, a chafe cover can be applied to protect the stay from further damage. 

As long as you keep an eye out for chafe, you will be able to catch any problems early and make the necessary alterations to protect it from chafing further. This way, any damage will be confined to grades 1 or 2 where there is no structural loss of strength yet.

Remember, dyneema is incredibly strong and is many times stronger than needed to hold the mast up since it is sized based on creep. Even if you catch a chafe point after damage has occurred, it will probably still be strong enough to get you home to make repairs.

The wonderful part of synthetic standing rigging is problems are very easy to spot. You never have to worry about a separated wire inside the 1x19 bundle, or stress hardening of your swagged fittings. Dyneema is just a fancy rope! If you are able to tell when a sheet or halyard looks torn up and needs replacement, then you can also look and tell when the dyneema stay is torn up and needs replacement.

To sum it up, chafe left unchecked can destroy the rigging. By checking the rigging often, you will be able to catch problem areas in their early stages before damage occurs and make alterations to protect it from further damage. Chafed areas also have tell tale signs that are easy to spot, as they appear fuzzy. External damage will occur but the internal fibers of the stay will be unharmed. Look at it often, and you will be able to fix it yourself allowing you to keep sailing, no matter where you find yourself!

Recap on Tuning of your Standing Rigging

Now that we have gone through how to adjust each stay, we will go over the whole thing so you can see how it all plays together.

You start by setting the length needed for the headstay and setting the mast rake.
Then you tension the backstay to tighten both the headstay and backstay at the same time
Now you make sure the mast rake is correct and the tensions are sufficient.

With that you are mostly done with the fore-aft adjustment. On to the side to side adjustment!

You start at the top and work your way down.

For single spreader rigs:

Cap Shrouds
Forward Lowers
Aft Lowers

Cap Shrouds make the mast head centered over the boat and keep it there while sailing. This stay is the tightest of the shrouds.

Forward Lowers are the following in the sequence and are tightened to induce a forward bend in the mast. They also adjust the side to side bend of the mast. They are looser than the cap shrouds but tighter than the aft lowers.

Aft lowers are the last to be adjusted and are set to straighten out any little curve that might be present in the lower section of the mast.

The shrouds in order from most tight to least tight are cap shrouds, forward lowers, aft lowers.  

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Now that you have finished this, it is time to go out sailing during light airs to make sure everything is fine, then again in stronger winds to test it out fully and make sure the mast stays in column while sailing.

If something is not set right, the mast will bend and you should fix it immediately. For this reason, I strongly suggest you test in light airs first, as they will not cause damage as easily as strong airs.

Imagine winds where you need to reef because a properly tuned rig is being stressed.
Now imagine that scenario where the rig is not properly tuned and starts to bend excessively! If the mast bends too far, it can kink and collapse! For this reason, always start off in light airs and move to stronger airs as a final check to make sure everything is perfect.

Tuning the Aft Lowers

The aft lowers are the easiest stay to set. They are the loosest stay on the rig compared to the others and take the least load. They attach just below the spreader and come down to the deck. Their purpose is to keep the mast in column as the boat heels over when the heads of the sails pull on the top of the mast.

If they are too loose, the mast will bend to leeward when sailing. This is part of the rigging is adjusted during the test sail.

For the dockside rig tune, you will tighten the stays until they are a bit looser than the forward lowers while making sure the mast stays in column. If there is any slight bow or bend in the mast, you will simply adjust that out using these stays.

If the mast bends to port, tighten the starboard aft lower a bit more.
If the mast bends to starboard, tighten the port aft lower a bit more.

That's all there is to that stay! It's not as complicated as it looks!

Tuning the Forward Lowers

Now that you have tuned your headstay, backstay, and cap shrouds, it is time to move on to the Forward Lowers.

These stays are not found on all boats, so if you don't have them, you can skip this section and move onto tuning the aft lowers (which in your case would be the "Lowers"). The purpose they serve is to help induce bend into the mast. They pull the middle of the mast forward while the backstay pulls the top of the mast back. This causes the mast to bend slightly, which is a good thing!

The sailmaker will want this bend, as it is important and calculated into the design of the mainsail. If the mast were straight, the sail would not fly as well. 

The tension on these stays will be less than the Cap Shrouds but more than your lowers. It is important to tension both sides at the same time and by the same amount to ensure that you don't pull the mast to one side or another.

If you are using turnbuckles, this will go very quickly and easily. If you are using dead eyes, then you will need to set up the tensioning line system.

As you go tightening, you want to sight up the mast to make sure it remains in column (which means straight). There are different ways to sight the mast, which we will go over at a later point as well. You will continue to tighten the stays while watching for the forward bend to happen and making sure that it doesn't begin to bow to the sides. This is why you want to do them at the same time.

For turnbuckles, you will start off

2 turns on port, 2 turns on starboard, sight the mast,
2 turns on port, 2 turns on starboard, sight the mast, ...

Once they begin to have some resistance, you will switch to

1 turn on port, 1 turn on starboard, sight the mast.
Proceed as needed until it is perfect

For deadeyes, crank the

port winch 1 full turn on high speed, starboard winch 1 full turn on high speed,
port winch 1 full turn on high speed, starboard winch 1 full turn on high speed, ...

Until the slack has been removed from the system. Then

port winch 1/2 turn on low speed, starboard winch 1/2 turn on low speed, sight the mast.
Proceed as needed until it is perfect

If the mast bows to one side, either tighten the side it bows from a bit more and sight the mast to make sure it corrected, or loosen the side it bows to a bit and sight the mast again to make sure it corrected.

If the forward lowers are tighter than the cap shrouds, you want to stop and reassess the situation. This is usually caused by a loose backstay. Since the mast is tipped too far forward, you need to crank down on the forward lowers to achieve proper mast bend. If this happens to you: 

Release the forward lowers
Tighten the backstay and possibly loosen the headstay to move the masthead aft.
Moving the masthead aft can make the cap shrouds slightly looser, so they will need to be readdressed. 
Then tighten the forward lowers again.

At this point, the forward lowers should be able to achieve the proper mast bend without becoming tighter than the cap shrouds. 

The next stay to set are the aft lowers

Tuning the Headstay

The headstay is very easy to set up, there are just a few points to keep in mind:

Too tight and it adds stress to the stem and mast fittings
Too loose and the headstay will sag
A tighter headstay is better for sailing to windward
A looser headstay is better for sailing down wind
You need to headstay to be longer than the luff of your headsail

With synthetic standing rigging, I like to set up the headstay and backstay at the same time. I set the rake with a slight aft bias and then tension the headstay and backstay until it feels right.

Once the right amount of tension has been achieved, simply tie the Shroud Frapping Knot on the headstay lashings and tiddy up the ends.

You will quickly know if the headstay is too loose, as it will sag and the luff of the headsail will fall to leeward. 

If it is too tight, the headsail will never sag. This may sound ideal, but the sails are designed to work with a bit of sag. If the headstay is so tight that it won't budge, it will place extreme stresses on all of the fittings and the sail will not perform as well as it could.

If you are not setting up the headstay and backstay at the same time, set the length needed on the headstay and when the backstay is set up, the headstay will subsequently be tensioned. The headstay and backstay pull against each other via the masthead, you should use this fact to your advantage when setting up your rigging.

I like to take advantage of an adjustable backstay to fine tune the headstay tension while under sail. If we are going to windward all day, I'll tighten the backstay adjuster. If we are running or broad reaching, I'll ease the backstay adjuster and let the headstay sag a bit, filling the sail with more air as it sags out into the wind. More about the adjustable backstay in a later post.