Quote:
Originally Posted by MasterMariner
So explain it to me than since you seem to think you know what you are talking about.
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As a starting approximation assume that a nylon
rode should have a breaking strength about the same as the
displacement of the vessel.
I found data on 160mm (6-1/4" dia) 8-strand nylon braid indicating a minimum breaking strength of 414,000kg (910,000) and 128mm (5") having 266,700kg (587,00lb) .
Nylon rope - Langman Ropes
So for the size and weight of vessel we are talking about nylon would be have a serious
storage problem.
Steel cable with 604,000 to 850,000lb breaking strength would be 2-1/2" to 3" in diameter. Having half the diameter means the wire take less than 1/4 of the volume to store.
http://www.wcwr.com/catalog/webcat.pdf.
So that's part of the attraction of wire. Also the wire has vastly better abrasion resistance so that is another big attraction.
The down side to the wire is the lack of give in the wire. Lets assume that snatch loads instead of being 10% of breaking strength as with nylon, they are more like 40% with a non-stretching material like steel wire.
To live with this at least 2 things have to happen:
1. The belaying point has to be massively built. In a steel boat this is much more economically accomplished, at least relatively.
2. When the vessel is anchored, there is always an anchor watch on duty. When the
weather deteriorates sufficiently, the
engine is run in forward to take a significant amount of the strain off the
rode thus reducing the snatch loads. The boats are only un-manned in very protected waters or when at
dock.
Being comparatively non-stretching also means that the steel does not generate as much heat when it stretches and it is less susceptible to heat damage.