Synthetic standing rigging, made out of Dyneema, is stronger than steel rigging but several times lighter. This allows your yacht to have less weight aloft while having more strength to hold the mast upright. The result of this is your yacht will become less tender and perform better in all wind conditions.
As if all of these facets of synthetic standing rigging were not wonderful enough, it has yet another shining attribute of greatness, it can't corrode!
Dyneema is made out of UHMWPE, which stands for Ultra-High-Molecular-Weight-Poly-Ethelene. The important part in that long word is Poly-Ethelene, another word for plastic. We all remember those commercials from the 1990's when they would show some miracle being performed, like saving a premature baby, or transporting clean drinking water, and they they would finish with "Plastic makes it possible." Once again, the world of plastics has had yet another breakthrough and can now create fibers that are stronger than steel, weigh next to nothing, and (since they are plastic) never corrode.
Your standing rigging faces a harsh life on a yacht. It is often ignored or overlooked while constantly bathed in moisture and salts. The stays are all crushed at the ends, making them grasp the wires as they slowly but surely begin to rust. In time, the corrosion will become so severe that the stay will break and fail, all because of a little moisture on its surface.
Synthetic stays are immune to this issue, as they will not absorb, nor will they interact with moisture on their surface! While freeing your mind from the concern of corrosion may sound grand, there is one weakness specific to synthetic standing rigging: chafe.
Chafe will break individual fibers on the stay, gradually weakening it until it will fail under the load it is frequently subjected to. Chafe, however, is easily avoidable. If you see your sheet rubbing on your stay, simply re-route your sheet to avoid this contact. If you know the stay will be chafed to carry out its task, simply add a chafe sleeve to it, or if the chafe will be severe, add service wrappings to provide an even more durable layer of sacrificial protection.
This is all well and good, but what happens if you overlook something? What if a part of your rigging becomes chafed quite severely before you notice it? How bad can it get?
While sheets chafing on your stays is bad (in the long run), they are not your worst of concerns. You should look at all items on your yacht as potential chafe offenders and secure them in a way that they can not cause any harm. I protected my headstay against chafe from the hanks, but I neglected to consider what could happen if chafe between the deadeye and the anchor occurred.
In this destructive experience, the anchor lept out of its roller and laid against the deadeye for 3 days while in a storm. The results were quite devastating.
First, the thimble that produces a nice and appropriately radiused bend was bent fiercely by the shank of the anchor. The Dyneema of the deadeye was the next piece in this destructive path. Several strands of the grommet were chafed through completely, making this component severely weakened and in immediate need for replacing.
The damage only occurred on one side of the deadeye, as the anchor only laid on one portion of it as it chafed away. This did mean that several of the strands were still intact, though they were weakened by the tight radius bend through the toggle. The toggle itself also appears a bit flustered by the entire situation, as surface rust is present (thankfully, the surface rust is actually rust from the anchor that rubbed off on the toggle) and the corner of the toggle is a bit rounded from the constant pounding. This constant impact will work harden the metal in the toggle and make it more prone to cracking in the future.
Now, while this damage may seem severe, it was easily avoidable by properly securing the anchor, and it was also easy and inexpensive to repair.
The cost of materials for a new deadeye are merely the cost of 4 feet of dyneema in the size you used. This particular deadeye was made out of 9mm SK-78 dyneema and the materials only cost around $20. The deadeye itself takes about an hour to make, making the entire repair not that intrusive on the wallet. Should a situation like this arise, I carry a "pre-made" deadeye in our box of spares, that way I can get straight to work and not worry about taking the time to manufacture one should the need arise.
While synthetic rigging is stronger than steel, it is quite fragile by comparison. Special care should be taken to ensure that no chafe occurs. If a component becomes chafed, you can always refer to this post for guidance as to its continued serviceability.
https://www.riggingdoctor.com/life-aboard/2015/10/16/how-much-chafe-is-too-much
Chafe is a fact of life on a sailboat, but thankfully it is an easily inspectable problem that shows signs externally, unlike steel rigging which can corrode away internally and only show problems that are detectable to a trained and professional eye.
One last point about the durability of Dyneema. This deadeye became severely chafed during a gale that lasted for 3 days. After the gale, we sailed 80 miles around Cape Hatteras in winds ranging from 30-45 knots and the deadeye remained functional, holding the mast up. We did not load the headstay with a sail, as that might have pushed it beyond its remaining strength, but we did fly a staysail and double reefed main in these wind conditions as we beat to windward. The deadeye was under intense and severe load during this ordeal, and yet it remained intact during the whole event. If chafe is a concern in your mind, let my misfortune of a mangled deadeye demonstrate to you that even in a disfigured state, Dyneema is rediculously strong and will stand up to the abuse to get you home safely!
