Deep anchorage experiences?

[noelex 77]

Originally Posted by LoudMusic

Hey I'm looking at possibly anchoring in 65 feet of water next summer. We have 200 feet of chain and what I'm seeing online (in particular DSII video) people are indicating the deeper the water gets a smaller ratio may be acceptable. I'd be getting around 3:1 on that. I think I'd be more comfortable putting another 200 feet of nylon on the end of that, but we'll see.

What experiences have you had with deeper water anchoring? What were the conditions and what hardware did you use?

You can manage with less scope in deeper anchorages, but the benefit is modified by the force on the anchor. Unfortunately, the effect of the advantage diminishes when the windspeed rises.

Anchor holding is actually dependent on the angle of pull on the anchor shank. Scope is just one factor in determining this. There are other important variables such as bottom slope that are often ignored when they should be taken into account.

At the moment I am anchored at just over 3:1 (3.2:1 just calculated) in just over 20m (65 feet of water). We have an oversized anchor, which together with the reasonably deep anchorage and only a very slight downslope makes me quite comfortable with our deployed scope despite the forecast of thunderstorms from 11pm tonight. However, as always there are variables. The substrate is usually the greatest unknown. This is especially true for a cruising boat constantly visiting new anchorages, particularly in more remote locations.

So rather than concentrating just on scope, try to consider all the variables.

[CatNewBee]

My biggest concern is not dragging, but getting stuck in an unmanageable depth where you need real diving gear to save the anchor. We have also an 60% oversized 85lb Mantus on our 40ft cat instead of the original 55lb Lewmar Delta. It will set and hold as long as you do not lift the shank almost everywhere.

[Dockhead]

Originally Posted by Chotu

I feel like a weirdo!

I'm always at 10:1 unless the anchorage is crowded. I was a bit nervous at 5:1 in a very crowded anchorage last week when a storm at about 40 knots blew through.

For deeper anchorages, I usually add nylon to maintain around 8:1-10:1.

Reading this thread, I guess it's overkill.

Well, scope is all good provided you have enough rode and provided you have room to swing.


10:1 in 17m of water would be 190m of rode (don't forget the 2m or whatever to your bow roller) -- almost a cable, making a swinging circle almost 2 cables around -- quite impossible in many if not most places with good shelter.


There's a table posted in the other thread, showing typical improvement in holding power as scope goes up. There are diminishing returns -- so not too much to be gained after 6:1. This varies according to anchor design; some modern anchors are much better than others in short scope.



Despite this I sometimes use more scope than that -- letting out more chain means more catenary and more weight and friction on the seabed. If I'm expecting bad weather I let it all out, if there's room to swing to my 100 meters of heavy chain. But if there's not room, it's really good to know how much you can get away with. With a good modern anchor, properly sized, you can get away with 3.5x or 4x in most situations, if you need to, but I try to get to at least 5:1 when I can.

[CassidyNZ]

Originally Posted by Chotu

I feel like a weirdo!

I'm always at 10:1 unless the anchorage is crowded. I was a bit nervous at 5:1 in a very crowded anchorage last week when a storm at about 40 knots blew through.

For deeper anchorages, I usually add nylon to maintain around 8:1-10:1.

Reading this thread, I guess it's overkill.

This sums up a few knowledgeable opinions:

West marine
Most anchoring texts and anchor manufacturers agree that a scope of 7:1 achieves the anchor's designed holding power, and more scope is better than less. In theory, 7:1 scope is great, but at a crowded anchorage most cruisers scoff at the idea of paying out more than 3:1 or 4:1

Thoughtco.com
The scope that is best for keeping the anchor set and keeping tension on the anchor rode is around 7:1. If we plug our numbers into the formula a water depth of 60 feet (18 M) will require a rode of 420 feet (126 M).

Seatime.com (for ships)
As a thumb rule, Scope of 6 is advisable for anchoring. That is when anchoring into a depth of 20 meters, we should pay at least 120 meters of cable. When anchoring in areas of strong wind or*current, we should have a scope of more than 6, up to 10 sometimes.

PBO
To keep the rode flat to the seabed you usually need plenty of scope. Accepted guidelines are three times the maximum expected depth of water for an all-chain rode, five times the depth for a combined chain/warp rode and seven times for a rope rode, but if you have the space, don’t be afraid to use more.

Anchoring.com
More scope means less vertical strain on the boat anchor thereby decreasing the chances of unsetting the boat anchor.*We generally recommend a scope ratio of 5:1 minimum, but ideally 7:1 (especially if anchoring overnight), i.e. let out 7 feet of rode for every 1 foot of water depth you're anchoring in, so if you are anchoring in 10 feet of water, you'll let out 70 feet of rode. Unfortunately, in small or crowded anchorages there's often not enough room to allow for a lot of scope.

Sailmagazine.com
Experts agree you need less rode if you have an all-chain rode. Some say 5:1 is good, some say you need 7:1 for real security, and others say 4:1 is fine. Britain’s Royal Yachting Association recommends that all-chain rodes be set with a minimum length of four times the water depth.

RYA.org.uk
The warp or chain is usually measured in either metres or feet.* Let out enough scope for the maximum depth at high tide, using the following a minimum guide:
* 4 x maximum depth for chain
* 6 x maximum depth for warp and chain *

Maybe 10:1 is generally speaking excessive for most applications but if you’re not swinging onto others, can easily retrieve and most of all, feel more comfortable, there’s no harm in it.

[Emmalina]

Anchored in 35m in Indo with 100m of chain out. Squall came through and a few boats dragged but not us. Hard work breaking the anchor out later though ! Chain serves no purpose in a locker .

[mikedefieslife]

I've anchored a few times in 18-21m with about 60-65m of all chain rode. It's not been a problem.

Often I aim for 4:1. Good luck with 10:1 in Europe's summer anchorages

[CatNewBee]

5...6:1 is fine with chain only. In the Med there are very shallow tides, so a non issue.It is important that the anchor resets easily because of 360 shifting winds during the day and night when using only 3:1 scope. at 5:1 usually the chain holds enough on wind shifts and the anchor remains set in the prevailing wind directionn.

[Sojourner]

Originally Posted by CatNewBee

It is important that the anchor resets easily because of 360 shifting winds during the day and night when using only 3:1 scope. at 5:1 usually the chain holds enough on wind shifts and the anchor remains set in the prevailing wind directionn.

This.... We anchor at 5-1 no matter what the forecast says. Even here in the crowded med. There is enough chain on the bottom that the anchor rarely resets in normal strength wind shifts...the chain drags around a bit, but the anchor stays set in the original direction. At 3-1 the anchor would be spinning in circles for days. A good anchor and conditions can take that of course, but I prefer it to stay put so I don't have to reset it. And yes, I dive the anchor daily, often twice daily (i like to swim / snorkel around the boat a lot anyway), and after any significant wind shift.