Anchoring Question

[caltexflanc]

You can find out the working load, capacity and stretch statistics of various sizes and designs and material of lines if you want to get all pedantic and paranoid about it. I use three strand nylon sized as if it was going to be anchor line, since under bad conditions, that's what it will be. Even on a double bridle, the boat will lay to one line or the other much of the time, and more so depending on boat design, and wind vs swell vs current. I went with about 25 feet myself. Everything went hunky dory in sustained 45knt, plus an hour or so at 60+ with gusts to 80 from a microcell.

I like all chain for a wide variety of reasons, ergo, I snub.

If you are a fair weather anchorer do whatever you like. The rodes on my 13' Whaler are chain/rope combos.

 

[Delfin]

I agree. But how long the snubber to be of any shock loading use?

So to keep the balloon pricked here, yes Muir and others sell snubbers, gear and equipment to protect the (weak and flimsy) windlass and charge dearly for their off the shelf connectors. But nowhere have I seen tables, charts and data to support "this is how long your snubber needs to be to keep your anchor from dislodging when the wind starts blowing."

It would appear we are back to the not so novel concept of oversizing the anchor to deal with big blows and the unknown snubber stretch with ensuing benefits concept. Or have a combination rope and chain rode with a big anchor then all bases whether real or imagined are theoretically covered.


So, how long are your snubbers?

Tom, while I couldn't find the reference now, I recollect reading in a technical paper on mooring lines for very large ships that a good rule of thumb is a reduction calculated by dividing the shock load by feet of stretch. So the question on how long a snub line should be is basically a function of getting as much stretch as possible, limited by a line size appropriate for the load limits of the chain used. If the shock load in gusts is 10,000# (quite a gust), then 4 feet of stretch reduces that load by 75%. 15% stretch is pretty typical for nylon lines without over stressing them, so if you want 4 feet of stretch you need around 30 feet of snubber. I assume that is why 30' is the most typical recommendation I recall seeing. This is also why I don't see all that much shock load reduction benefit from bridles, because they are generally only a few feet long. Naturally, if you have all rode, you have all snubber.

I use a 30'. The snubber is made of a short bit of dyneema mated to 5/8" nylon brait with an Ultra snubber that basically just acts as a visible indicator of load. The more the rubber is stretched, the greater the loading on the snubber. It is joined with a Plasma soft shackle that takes me about, oh, 3 seconds to attach to the chain, is stronger than the chain, and can't fall off. The whole line feeds out over a roller above the chain roller so it is always fairly led.