Chafe is one of the most common causes of mooring and anchoring system failure, and it’s one of the reasons chain has been valued for as long as boats have anchored. Wherever rope is used, friction between the line and the contact points it has to cross produces wear and heat. Once the forces in the line are high enough, both become serious.
The obvious danger is bad weather and rough water. But chafe is also cumulative. UV damage and microscopic wear on the fibers add up over seasons, and a line that looks serviceable can already be well down on strength.
Forces in rode can be substantial. I’ve used these line and block variations often. Bad gusts in Porto Santo, Madeira… good quality 1″ polyester burned through (chafed) in about three minutes and shrinking (stretching) from 1″ to 1/2″ with the surge loads. Only thing that would work was a snatch block. Plastic tube burned straight through.
— Peter Smith, Rocna designer and professional sailor
Three minutes. That’s what chafe can do at the severe end, to good rope, with a guard fitted. The techniques below run from routine protection through to the arrangements that hold up in those conditions.
Chafe guards
[IMAGE: Chain-stop_and_snubber.jpg — “Chafe guard on snubber led over port roller next to chain.” Shared with the snubbers article.]
Flexible PVC tube or something similar takes the abrasion sacrificially, in place of the rope. Tie it in position with light string so it can’t slide along the line and leave the wear point exposed.
If the line is going to stretch much, tie the guard in position relative to the fairlead or chock, which means to the boat rather than to the line. The contact point stays put. The rope moves through it.
PVC can burn or melt through under serious load, as above. A better solution is fabric reinforced rubber hose, and exhaust hose works well. Wire reinforced versions work too.
Chafe guards don’t solve the problem, they make it manageable. They’ll wear through eventually and need replacing. Watch the underside of the hose, which is where the wear happens and where you won’t see it without lifting the line.
Holding the line clear
If you can keep the rope from touching the contact point at all, there’s nothing there to wear.
A small secondary line can hold the main rope mostly clear of the point it has to cross. Where the angle is shallow, such as a rode deployed at high scope, this takes the bulk of the abrasive contact off the rope. That small line then carries a share of the total force in the rode, and elementary trigonometry gives you how much, but at a shallow angle that share is small. More to the point, nothing in the system is any longer moving lengthways against a hard surface, and if the small line does fail, nothing dangerous happens.
Tie the secondary line directly to the main rope, or around its chafe guard, or to a snatch block that the rode passes through. The block or the guard stops the secondary line crushing the rode, takes out the pressure concentration, and softens the change of angle.
Fail-safe chain
If rope is doing the work as a snubber and the chain hasn’t left the foredeck, secure the chain in a chain stop anyway, even though there’s no tension on it.
If the rope fails, the chain then won’t shock load the windlass as it takes up.
Splicing in a chain section
Splice a short length of chain into the rode at the wear point and it will never fail on account of chafe. Cover it with tube as above if you want to protect the boat.
The same reasoning applies to any critical part of a rode that’s prone to chafe. Mooring lines are the exception, because metal and chain shouldn’t sit permanently at the water’s surface. Kept above the water, it’s ideal.
In an emergency
Vaseline, silicone grease, or failing that generic grease rubbed into the rope will substantially reduce chafe. This is an emergency measure.
Rope types
Different ropes handle chafe differently, though every rope needs chafe protection. Rope construction and material are covered in the Titan guide to choosing an anchor rode.
Chafe when on moorings
Moorings bring a related problem, and it turns up the moment the anchor is sitting unused on the bow.
The section of rode running from the mooring to the boat has to stay safely clear of the anchor. An anchor on a bow roller is a hard object with edges, sitting exactly where the mooring line wants to run. Moving the anchor off the roller may be enough. Sometimes you have to take it off the bow entirely.
[IMAGE: Chafe_by_anchor_when_at_mooring.jpg — “This line will chafe on the anchor.” Photo courtesy R. Collins, permission to be confirmed. See CH-02.]
[IMAGE: Santa-Maria-Australis_on-mooring.jpg — “This Rocna has been moved off its roller to avoid chafing the mooring line.”
Two other spots are still waiting on links, both logged under GEN-01. The snubbers article references chafe protection in its own section, and the chafe article’s fail-safe chain section refers to a chain stop. Both need rocna.com URLs once the pages exist, so they can only be filled after publication order is decided.