Effect of chain on anchoring

[carstenb]

Your reason for running the snubber the entire length of the boat is to get as long a snubber as possible? Good idea

[JonJo]

Originally Posted by carstenb

Your reason for running the snubber the entire length of the boat is to get as long a snubber as possible? Good idea

Yes, its maximum length, the flat of the deck length + distance between one bow and centre of forebeam. Initially we simply attached the chain hook in the centre but now we've end for ended it we use bowlines. We have about a 1.5m tail - which gives us a bit of play if we get wear at the chain hook end. For a monohull you could simply use one side deck, unless its a beefy mono in which case you might have one down each sidedeck. Because the snubber runs through the stanchion bases its clear of working area and no more of a nuisance than a headsail furler line. We use a turning block on the bow but for a mono you might arrange to run though a fairlead or over the bow roller and I'm guessing you would need some hosepipe to protect the snubber from wear. We use 12mm nylon, becuase that's what we had 'spare'. I might go down to 10mm (38' cat 6t in cruising mode). It would take the load, give more elasticity but might not last so long. We carry enough nylon to make up another, and use it to tie to trees when necessary.

There is one other advantage - we have a line (the sunubber) down both sidedecks at the hull/deck interface, just right to hold onto if you need something to hang onto when in a dinghy alongside. Though if yuou have a modern high sided yacht (or cat) it might still be impossible to reach.

J

[Lagoon4us]

So the idea is solely to get the most elasticity from the long length without having an overly acute triangle.

Is there any downside in the height where your bridle is coming around the turning blocks and heading down rather than from a low-down point where a normal bridle's eyes are attached?

I would have speculated that the lower point scoots the boat forward a little but offers the bows in more a heads up attitude whereas from the turning block on deck it would tend to pull the bows down more?

Interesting stuff!!

[carstenb]

I'm planing on using climbing rope since it is very elastic. Let's say I get 15% stretch. Length of my hull from aft cleats to bow is about 38 feet x 15% = roughly 6 feet. Add another 3 feet of snubber to get clear of the bow. Meaning I then need to fix the snubber at least 10 feet out the chain?

[JonJo]

Originally Posted by Lagoon4us

So the idea is solely to get the most elasticity from the long length without having an overly acute triangle.

Is there any downside in the height where your bridle is coming around the turning blocks and heading down rather than from a low-down point where a normal bridle's eyes are attached?

I would have speculated that the lower point scoots the boat forward a little but offers the bows in more a heads up attitude whereas from the turning block on deck it would tend to pull the bows down more?

I'm planing on using climbing rope since it is very elastic. Let's say I get 15% stretch. Length of my hull from aft cleats to bow is about 38 feet x 15% = roughly 6 feet. Add another 3 feet of snubber to get clear of the bow. Meaning I then need to fix the snubber at least 10 feet out the chain?

I'm not sure where 'normal' is for catamaran bridle attachments, our original attachment points are on lugs under the cross beam, which is one of the strongest parts of the yacht. Our turning block attachment is adjacent. Your bridle is going to take all the load and you simply need to ensure the point of attachment is fully reinforced.

I think it unlikely you will enjoy 15% elasticity. Most nylon stretches around 25% but that's just prior to failure. You would need to look up elasticty of your climbing rope but it would be 'unusual' if you were to enjoy loads of 500kg, check what elasticty you have for your climbing rope under a load of 500kg. The longer you can make the bridle, the more elasticity (length not %) you will get. You'll need to play around with the length of loose chain, one way to find out is to reverse up at full revs, work on about 100kg of thrust per 10hp on engine - very approx.

J

[tenchiki]

Does anyone know what happened to http://tubafour.com/chain/model.html? It recently stopped responding. Did it move? Did anyone save a copy? archive.org only has some of the pages...

[Polux]

On one of the recent editions of the sail magazine Voile and Voiliers there was an interesting anchor test different from the usual. They tested the same anchor with chain, chain and cable, plumbed cable and just cable.

Very interesting conclusions. Off course the best results were obtained with full chain put they were not proportional to the weight used.

I would have liked to see the results if two different chains were used, a 8 and a 10, for instance but they did not went that far.

As most know it is possible to have a high grade 8mm chain as strong as a "normal" 10mm one and in that case 75m of 8mm chain weight less than 50m of 10mm chain.