Anchoring question

[thinwater]

Originally Posted by dangerfield55

It doesn’t address the thought that the heat caused by stretching of nylon during a storm is a cause of failure but if the fetch and waves are limited so might the heat. Again Interesting.

I read a lot about heating, but there are two problems:

a. If you pull test a nylon rope at low speed the end melt. This is cause by energy release at the moment of rupture. Thus, a photograph of melted ends does not mean anything. You can run this test yourself.

b. The math does not work for anchoring. If you look at the energy per length and the frequency, and consider heat disipation estimates, the rope won't even get warm. The frequency is too low. Dock lines, yes, but not anchor lines. Don't belive the math? Read this study. http://www.dtic.mil/dtic/tr/fulltext/u2/a194750.pdf

What you are seeing is fatigue failure. Nylon cannot sustain more than ~ 10% BS for too many cycles. In fact, the ABYC H40 nylon rode tables are based on this.

What does cause significant heating is friction through chocks and jammed polyurethane rollers. This is why you see heat failures under rubber chafe gear at docks. The math works there. But it takes a big storm and relatively high frequency bouncing. Read the above study.

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And please, if you can show me a study or math that supports heating in a quantitative way, PLEASE post it. I don't believe it is impossible, but it needs measured proof, not a photo of a melted line.

[dangerfield55]

Thanks

[zboss]

Originally Posted by waeshael

The length of the rode needed is a function of the water depth and doesn't depend up the type of rode material. A burying anchor works by being slowly sucked under the sand, and requires a particular angle for the rode. For instance a CQR requires a 7 degree slope. This means that the length of the rode must be about 8 times the height from the bowsprit to the sand. Any steeper angle and the CQR begins to pull out and not slide deeper. Whether you use chain to do this or nylon makes hardly any difference because under load when the wind blows the chain will be straight like a rod and there is no benefit from its weight - it has no catenary. Anchored in 20 feet of water with 5 feet from the LWL to the bow requires a rode length of 8 x 25 = 200 feet. Now, since you have no idea what type of anchor your neighbor is using and his rode length, you have to make sure you are well clear, because if he has miscalculated his anchoring system it will drag in a blow.
Now you can reduce rode length with special anchors that bury at higher rode angles, such as a fortress.
But generally speaking in 20 feet of water you should see a 200 foot rode.

If you are using all rope rode you better be using 7:1 to 10:1 whereas you can use 3:1 up to 5:1 with all chain for tight to regular anchoring. We use 5:1 most of the time but also regularly use 4:1 in crowded anchorages, along with everyone else.

Then you get some dude that refuses to use chain and ends up having a 450 foot swing radius? That’s unfair to your fellow cruisers and you should find someplace else to anchor. We had one guy in key west, which has notoriously bad holding, with 350 feet of all rope out because that is what he needed to not drag. So an anchorage that is only 700 feet across and can normally support a dozen vessels all had to move out of this guys way.

At least get a Kellet or something.