Anchor chain scope, double the depth?

[reed1v]

For peace of mind, and with a hydraulic windlass, we went with the old 7:1 ratio whenever possible. We also were religious about using a kettle to keep the chain as close to parallel with the bottom. One less worry. If you got it, use it.

[nigel1]

I recently visited friends on the Isle Of Mull, Scotland, who have a large mussel farm in Loch Spelve, which is renowned for some really strong winds.
They let me have use of one of their mooring buoy's which is designed for a 100 tonne workboat, so no worries there.
They did tell me that every year they watch a dozen or so yachts drag across the loch, and luckily for the owners, the boats usually fetch up against one of the strings of mussel ropes, preventing a grounding.

[JOHNMARDALL]

Rules of Thumb if we're talking all chain, 4:1 is minimal, 7:1 is safe in most conditions, 10:1 is safe in stormy weather, but if you've got more chain, put it our, providing you're not going to foul other boats. Even with excellent scope, the anchor can still drag so you've got to set an anchor watch, either with a GPS based alarm or a human watch-keeper, who is taking bearings on shore points and watching the GPS.

The price of freedom is eternal vigilance.

John Mardall
Vetus Maxwell Group

[JOHNMARDALL]

Originally Posted by reed1v

For peace of mind, and with a hydraulic windlass, we went with the old 7:1 ratio whenever possible. We also were religious about using a kettle to keep the chain as close to parallel with the bottom. One less worry. If you got it, use it.

I think that's a kellet.

[TurninTurtle]

Heavier anchor & chain... lower multiple of depth NEEDED to keep the boat in place for the same conditions.

Different bottom conditions will affect how well the anchor holds.
Different wind/current can require different scope.

Shorter line between chain and boat means less wind/current before the chain is lifted all the way to the anchor. Then the chain isn't doing its job of helping the anchor dig into the bottom. You really want a good length of the chain to be on the bottom.

[Vasco]

Originally Posted by JOHNMARDALL

I think that's a kellet.

Not an old kettle filled with lead? In the distant past I've used milk jugs filled with sand to weigh down my nylon rode so I didn't get keel wrapped.

[dick sargent]

What do you call the weight that slides down the anchor chain to adjust catenary? I carried a 25# lead ball for 20 years but never used it.

[savoir]

A kellet

[sailorboy1]

Originally Posted by Vasco

Stay up, keep an eye on things and be ready to weigh anchor quickly and get the hell out of there.

Probably too late to go out and that would into the storm.

[Cheechako]

Originally Posted by denverd0n

This ^^^^^.

Unless you are in a very crowded anchorage, what good is trying to get by with the very minimum scope? Put out 5:1 or more and sleep easy.

The calculations are simple. In 15' of water with about 4' of freeboard? Call it 20' altogether, times 5 equals 100' of rode. How hard is that?

[S/V Alchemy]

Originally Posted by boatman61

Lay what you like..
Personally I've always laid LWLx3+depth... was taught that by an old salt in the 60's and adhered to it.. has served me well over the years.

Wait, so with 30 feet of LWL in 20 feet of water, you'd lay out 110 feet of chain, but in 10 feet (assuming no tide), you'd lay out 100 feet?

[ramblinrod]

Originally Posted by sailorboy1

The thing with scope ratios is that they don't take into account anchor type, weight, and holding. But far as practical I have found it rare to be able to put out more than 4:1 just due to other boats and swing room.

What do people do in a crowded anchorage with little room do when a front is coming in and there isn't room for using more scope?

If any kind of wind is expected,
Put out a second anchor.

[S/V Alchemy]

Originally Posted by sailorboy1

The thing with scope ratios is that they don't take into account anchor type, weight, and holding. But far as practical I have found it rare to be able to put out more than 4:1 just due to other boats and swing room.

What do people do in a crowded anchorage with little room do when a front is coming in and there isn't room for using more scope?

Head to sea.

[Vasco]

Originally Posted by sailorboy1

Probably too late to go out and that would into the storm.

It's better to be out there bouncing around with a bit of sea room rather than in a crowded anchorage waiting to drag or to be dragged down on.

[S/V Alchemy]

Originally Posted by Stu Jackson

Maine Sail did a great analysis on his website showing the affect of additional rode on angles of pull. It's simple trig.

Nigel's right. He wrote: I've been stuck in a bay with sustained winds of 40kts, gusting to 50, with a scope of 8:1 and felt pretty secure. At 4:1, I would have been crapping myself

Same thing happened to me a few months ago, I started with 5:1, it started howling, let out 10:1 and stayed put for two days.

Chain is cheaper than boats, and hauling chain is less laborious than earning enough to buy boats.