Dyneema is a wonderful material for use on a sailing yacht for standing rigging. It is immune to rust and corrosion, and it is incredibly light weight! Placing it at the stem of your yacht, where salt spray and moisture are a daily fact of life is a wonderful idea as this powerful plastic will take the charge and never let you down.
While it may seem that synthetic standing rigging has no weaknesses, this would be false. Synthetic standing rigging has one tragic weakness that can destroy it in a moment: chafe!
In a gale, our 65 pound Mantus anchor broke out of its roller and gnawed on the deadeye for three days. The damage suffered to the headstay was extensive and precluded us from using our headsail as we limped along for 80 miles to return to shore.
The shank of the anchor chewed and chafed on the dyneema deadeye while also mangeling the thimble inside the lower part of the deadeye.
If the damage to the dyneema had been less extensive, it would still had been risky to load this stay as the thimble was no longer in function.
The purpose of the thimble is to smooth the bend at the bottom portion of the deadeye. Dyneema is strong, but sharp bends will cause the fibers to crack and break, leading to premature failure.
We have a cutter rig, meaning that we have a second headstay further inboard, but it is by no means destined to resist the forces of the backstay and sails while trying to power to windward. These forces fall onto the headstay and are rather extreme, especially when the stay is further loaded with a large jib in high winds.
Our rigging was crippled and we were 50 miles off the coast in a gale with another more powerful gale on its way!
Now, to ensure this doesn't happen to you, there are a few suggestions I would like to make.
First, if you are going off shore, stow the anchor somewhere away from the headstay. We keep various anchors that we use infrequently tied to the boat, and when heading off-shore, your bow anchor should be treated like any other anchor as you won't be using it for some time. With your anchor secured and tied up very well, it won't be able to leap out of its roller and chafe away on your standing rigging.
Another trick would be to install a sacrificial piece in front of the deadeye. This would take the damage of anything that wants to destroy your rigging by getting destroyed first and hopefully you will find the problem and correct it before it gets worse. This line could be attached through the eye of the headstay and simply run down to a further forward hole in your stem fitting.
To ensure that you will be able to make it home, it would be a good idea to carry a spare deadeye, already assembled with its thimbles and the fairleads needed to tension your rigging. If you lose your headstay, you are at the mercy of the currents! Having the tools and parts on board with you will grant you the ability to make it back to port on your own.
The reason to have a deadeye already made is because they are rather tedious to make. I take about an hour to make one in calm conditions, at home, with no stress of a storm situation. Imagine trying to make one of these while out at sea as you worry about where and how fast you are drifting? Having it already made will also reduce the amount of time it will take to install the new deadeye, which sadly is a rather lengthy process. Headstays require a lot of tension and can take close to an hour to setup with a deadeye.
Now, if you would allow me to lead by example on this front. This damaged headstay occurred on my own personal yacht that I rigged several years ago with synthetic standing rigging. I carry all the tools and parts needed on board to rig her again at sea if we needed. I also feel that I take every precaution possible to ensure the longest life for the rigging. This situation occurred and I can not guarantee that it won't happen again, so I am converting my headstay with a deadeye to a turnbuckle. I feel that a piece of bronze with stainless steel screws will hold up better should this freak occurrence happen again. We will certainly be restraining and stowing the anchor differently from now on to hopefully eliminate any other anchor related damages, but accidents are never planned and I feel that a piece of metal is a better security blanket than a piece of rope at the lower part of the stem.
Synthetic standing rigging is awesome and deadeyes take away any fear or concern of corrosion, but the pulpit is a dangerous place when laying right next to the anchor. If you have a racing sailboat where the anchor is not stored on the bow, or your anchor roller is far away from your headstay, then by all means, keep with the peace of mind of deadeyes. If you have a similar setup to mine, then strongly consider setting it up with a turnbuckle and be sure to oil and inspect it regularly and frequently for any signs of corrosion.