Assuming the line you are planning on using is nylon, the worst thing you can do is add a plastic cover Over it for chaff protection.
While it used to be thought that plastic sleaving would protect against chaff, reviews
of the primary failure mechanism of dock
lines during hurricanes has shown a few things relavent to sea anchors.
1) strength was almost never the problem
2) chaff, particularly chaff at the chock where the line came onto the boat was overwhelmingly the favorite point of breaking.
3) the primary cause of breaking has been ascribed to a few things.
a) as the nylon stretches over the chock it is doing so under tremendous loads. This friction of course causes significant heat in the line.
b) plastic covers act detrimentally in two ways, first they act as an insulator to keep the heat from being carried away by water
and air convection currents. And they add another friction point for the line to rub against.
Currently there are a number of systems in the works for dock
lines that use a two piece line. Nylon from the piling to just before the chock, and then dyneema/spectra spliced onto the end that carries the load aboard.
Unfortunately there just isn't a way to do this for a sea anchor
, but it does inform the decision of how to use it. First keep coverings as far as possible from nylon lines as you can. If you use use one, ensure it is a breathable one that will allow heat to dissipate. Finally try to keep the bending angle between the cleat and the load point (the anchor) at as shallow a bend as possible. This reduces the friction load at the chock.
For a sea anchor my advice would be to start with more line out than you feel you need (let the boat rest one wave more downwind than you could), and slowly over time shorten the line. This will keep moving the damaged portion of line onboard instead of further out (like letting the line out over time will). Even a few inches an hour could make the difference, and probably won't change the ride of the boat much.
If you can, moving the cleat to the toe rail would probably be the best option, but that is obviously a major job.
Originally Posted by charliehows
yeah Ive just been reading eric hiscock on this very subject and he says chafe is the big problem - he recommends putting heavy plastic hosing over the inboard end of the lines to protect them - failing that wrap them with towels taped over.