Anchoring

[lionelz]

Well hopefully not a stupid question

I get the issue with letting out enough chain or warp, ratio 4/6 but my question is why such a ration? and also do you let as much out as there is water when you anchor out and leave it or do you change it every hour as the tide comes and goes? I have not yet been brave enough to try to anchor up, but I want to do an overnighter somewhere (yet to be decided) I have enough chain/warp to go into about 8m of water, I have also checked that it is attached to the boat (I had visions of it being let out and then seeing it disappear over the side). So just checking before I start to make plans.

 

[Deleted User YDKXO]

Good question. The accepted wisdom is that you put out as much chain as you think you need for the highest tide you will experience. That means at low tide you will have a greater scope of chain out than at high tide. That does create a potential problem though because at low tide you will swing around more than at high tide so make sure you are positioned well away from other boats around you if you are expecting a large tidal range. With regard to the scope of chain you put out there is no hard and fast rule. Again the accepted wisdom is 3:1 but you might put out less chain in a crowded anchorage in calm conditions for a quick lunch stop or you might put out a lot more for an overnight stop in an anchorage when wind is forecast and you are not sure about the holding of the sea bed. Also in a shallow anchorage you should put out more chain than just 3:1 and in a deep anchorage maybe less. Also if you are using part chain/part rope, you should use a higher scope

Yes the end of the chain should be attached to the boat with a short length of rope (known as the bitter end) which can easily be cut in the event that you need to leave an anchorage quickly and for some reson you can't get your anchor up. But this rope should not be used to hold the chain to the boat when anchored and neither should the anchor windlass itself because the anchor windlass generally has some form of clutch which may let go unless properly tightened down. You should always tie back the chain to a mooring cleat or use some form of snubber to hold the chain. Again most people don't do that for a short lunchtime stop but it should certainly be done for an overnight stop

 

[jac]

The 4:1 5:1 or even 6:1 ratios are really just a handy rule of thumb. It's actually quite a complicated maths formula to calculate chain catenary and for obvious reasons most people don't want to do advanced maths whilst anchoring!

The need for 4x ( or more) is that the anchor only holds properly when the pull is horizontal. If you put out 1x, the anchor would be pulled straight out of the bottom and it needs a fair bit of weight to ensure that the pull is always horizontal.

In terms of how much to let out - assuming you have space.

Work out how much water there is still to rise until high tide and add that to the depth now. Work out how big the height at high tide will be from sea bed to your foredeck and let out appropriate amount of chain. usually get away with 4x if all chain or 5x if rope & chain.

Example.
Depth is 3m. Your foredeck is 2m above the waterline, there is still another 1m to rise until high tide.
You need to let out 4x (3+2+1) = 24m of all chain.

In a really tight anchorage you might need to lay to less at low tide but it is a lot of work to do that if staying for a couple of tides. so get the space right first.

Finally remember that anchoring etiquette is that the late arrivals should keep clear of the early arrivals and in any conflict ( i.e. boats getting too close) then the last in should move first.

 

[Tranona]

If in a tidal area you calculate your amount of chain in relation to the deepest water you expect. So it the chart shows 8m and you have a 3m rise you use base of 11m. The actual ratio of chain to depth is not a fixed amount as it depends on the boat, the anchor, the weather etc, but a minimum of 3* depth up to 5* depth - more better than less. However the more you have out the bigger your swinging circle which can be a nuisance in crowded anchorages. So in 8m of water you need at least 30m of rode - does not all need to be chain, but makes sense to have at least 50m. If you are anchoring in areas which have a big range such as the Channel Islands or the Bristol Channel then you will need more and you may want to adjust the amount out depending on the state of the tide.

 

[noelex]

The scope is one of the major factors that determines the holding power of the anchor. The higher the scope, the better the anchor's holding power, but at some point (around 10 -14:1) the effect of more scope becomes very slight.

The formula for scope is always the total rode divided by the current depth of water in which the anchor is lying plus the bow roller height. Note the bow roller height needs to be included and also note it is the depth where the anchor is sitting not where the boat is lying.

So if you drop your anchor in 8m and there is 1m from your bow roller to the waterline you need to let out [(8+1) x5] = 45m of rode to have a scope of 5:1 . This means as the tide rises and falls your scope will go up and down accordingly. If all other things are equal this also means your anchor's potential holding ability is also varying with the tide.

If the tide rises 1m from the time you dropped and you don't alter your rode length the scope has gone down to 45/10= 4.5:1. If the tide falls 1m from when you dropped the scope has gone up to 45/8= 5.6:1.

The most common way to cope with the changing scope when anchoring for longer periods is to calculate the scope at high tide and put out sufficient rode so the scope will be adequate. As this is a worst case scenario the actual scope will always be equal or better than this. In most areas of modest tidal range this is an easy solution. In areas of large tidal range if there is restricted swinging room the rode has to be adjusted periodically. Of course you may also have to adjust your scope for other reasons. Unexpected bad weather may mean your chosen scope may become inadequate and you may lengthen the rode to give a greater scope and the anchor higher holding power to cope with stronger wind.

Selecting scope is dependent on the weather conditions, your swinging room, what nearby boats are using, the holding ability of your anchor in the particular substrate and its performance at various scope ratios as well as the slope the anchor is sitting on. (This latter factor is often incorrectly ignored). If you are anchoring at short scopes or with an anchor that has poor holding ability the water depth and rode composition also play a significant role. This sounds complicated, but in practice a rough mental weighing up of these factors is all that is used. As you can see from the table the anchors holding ability does not change rapidly at moderate to long scopes so the difference between for example 5:1 and 5.5:1 or even 8:1 verses 10:1 is largely academic. However, you do need to more precise if you need to use short scopes.

There are some tables that give you some idea of your anchor's potential holding ability based on the scope used. These are only a very rough guide and will vary with different design of anchor etc. But the table will give you some idea.

Scope. Holding ability.
2:1 10%
3:1 40%
5:1 70%
7:1 85%
10:1 100%

 

[Hurricane]

Just adding to Deleted User's comment about taking the strain off the windlass.
Most windlasses are driven by a gear and a worm gear.
So, apart from the clutch that Deleted User refers to, the boat would only be held on the teeth in that worm gear.
After stripping ours, we always now rig a bridle to take the chain's load off the windlass itself.
There are various ways of doing so.
Some involve stainless steel deck fittings but just use a simple chain hook and some rope.
Recently, Jon Mendez did an excellent video showing these methods
see here
http://www.mby.com/training/cruise-further-cruise-safer-anchoring-overnight-43648

 

[Mike k]

Following on from Deleted User a thing that has served me well is a Y shaped rope bridle with two soft eyes to connect to your forward cleats and a thimble and shackle on the front to connect onto your chain. A rope supplier made it up for me. Takes all the strain. We anchor in the Mersey with a strong tidal flow and use 8mm chain on a 3 or 4:1ration with a 4kg delta 25 foot plastic boat with only an occasional glitch.I once had to handball the chain in when my windlass failed and I never want to do that again so I don't risk putting the windlass under too much strain and always motor forward on the retrieve so the chain is always slack.

 

[Hurricane]

Following on from Deleted User a thing that has served me well is a Y shaped rope bridle with two soft eyes to connect to your forward cleats and a thimble and shackle on the front to connect onto your chain. A rope supplier made it up for me. Takes all the strain. We anchor in the Mersey with a strong tidal flow and use 8mm chain on a 3 or 4:1ration with a 4kg delta 25 foot plastic boat with only an occasional glitch.I once had to handball the chain in when my windlass failed and I never want to do that again so I don't risk putting the windlass under too much strain and always motor forward on the retrieve so the chain is always slack.

With a bridle, there's another trick I use.
After you have set the bridle, you can let out more chain so that it creates a loop behind the point where the bridle attaches to the chain.
This has the effect of lowering the chain - a bit like yachties use a chum.
The point at which the chain pulls can sometimes even be below the water surface.
You do need to make sure that the loop is well clear of the bottom, though, or it could catch.

See here

 

[Jonmendez]

"Recently, Jon Mendez did an excellent video showing these methods
see here
Read more at http://www.ybw.com/forums/showthread.php?426598-Anchoring#Ut6i1C2IHkZu7A78.99"

Thanks Mike, also thanks to Lester who shot it and Jack who is the editor. I am only part of the team!
J

 

[Deleted User YDKXO]

Following on from Deleted User a thing that has served me well is a Y shaped rope bridle with two soft eyes to connect to your forward cleats and a thimble and shackle on the front to connect onto your chain.

Osculati make a purpose built chain snubbing hook here
https://www.jimmygreen.co.uk/products/chandlery/anchoring-accessories/custom-chain-snubbers

 

[superheat6k]

Anchoring first time for an overnighter is always daunting, and for occasional anchorers the tension doesn't ease that much.

Use your plotter to set an anchor watch, and use simple transits to check you are not dragging. If you do drag it wil be away from the chain, but if tide slacks you could easily creep forward or similar as you swing, which can be unnerving.

The rule of first come moves last is of high importance, as boats may be some distance off when setting their anchors but can have considerably different scopes, and hence swinging circles, so as the tide turns you find yourself sitting over someone elses cable, or even on to or under them.

If you suspect the anchorage will get busy (e.g. Bournemouth Air show), the panorama feature on your mobile phone is invaluable to prove who was there when you arrived. If you lay out 50m in say 8-10m then swing say 85m onto some other boat, who only laid out 20m, he will likely try to claim he was there first. I had words with a 22' yacht at the Bournemouth show because of this, and the skipper got very uppity with me when I suggested he let out some more scope before my davits had his forestay & mast out, but I had arrived very early and had a clear 100m right around me.

 

[Nick_H]

Following on from Deleted User a thing that has served me well is a Y shaped rope bridle with two soft eyes to connect to your forward cleats and a thimble and shackle on the front to connect onto your chain

Is there a reason you use a shackle instead of a chain hook, if that's what you were suggesting. If the weather suddenly picks up rough you want to be able to leave an anchorage without any delay, and a shackle can be awkward as you generally need to get it up onto deck to open it with two hands, and they can even bend or cross thread and be difficult to open. The beauty of a chain hook is you can easily remove it just by releasing the tension on the bridle.

 

[Hurricane]

Is there a reason you use a shackle instead of a chain hook, if that's what you were suggesting. If the weather suddenly picks up rough you want to be able to leave an anchorage without any delay, and a shackle can be awkward as you generally need to get it up onto deck to open it with two hands, and they can even bend or cross thread and be difficult to open. The beauty of a chain hook is you can easily remove it just by releasing the tension on the bridle.

Agreed - in fact recovery is easier than setting it.
Also adding a couple of rubber snubbers reduces any snatching.
We use the bridle every time now - even if we are stopping for just a few minutes.

 

[J Neeves]

If you want to reduce snatching the best thing to do is use a longer snubber, or better - 2 snubbers or bridle. Short snubbers really only allow the load to be taken off the windlass and onto another strong point. if you have long nylon snubbers they introduce elasticity. In order to 'get' length you can have the nylon extending from the bow or start the snubber at the transom, run up the side decks and then over the bow roller (or though fairleads) to a central chain hook. If you do not believe in any of this - think of a bungy jumper. When they reach the bottom of their leap (of faith) they feel very little (except relief) all that momentum of the fall is absorbed by the bungy cord. Just think what would happen if the bungy cord was all chain. Now think of your snubber as a bungy cord for a boat.

Too long a line off the bow can allow the snubber or chain hook to drag on the seabed (and fall off) - hence the transom attachment.

Adding rubber snubbers is equivalent to extending your snubber by 2m. I know which is cheaper.

You should still secure the chain to a strong point other than the windlass, snubbers fail.

Jonathan

 

[lionelz]

Thanks guys, some really good points there, makes you relize that was I was taught on my boating courses only scratches the surface and there is no substitute for trial and error and plenty of practice. I am hoping to do the bournemouth show this year so that could be interesting

 

[blueglass]

Much excellent advice on this thread but there is a downside to the use of snubbers/bridles etc. Sometimes you need to get that anchor up and get away quickly if there's a sudden unforecast overnight change in weather.(happens in the med not infrequently)
Messing around in the dark on a wildly pitching bow undoing snubbers etc is not always helpful. Such an experience some years ago caused me to think that out again and hitherto have relied on my windlass and never had an issue.

 

[Mike k]

Is there a reason you use a shackle instead of a chain hook, if that's what you were suggesting. If the weather suddenly picks up rough you want to be able to leave an anchorage without any delay, and a shackle can be awkward as you generally need to get it up onto deck to open it with two hands, and they can even bend or cross thread and be difficult to open. The beauty of a chain hook is you can easily remove it just by releasing the tension on the bridle.

Hi Nick
I know what you mean but my first bridle came with the shackle and I have just stuck to that. My problem is I need to go on the bow each time I set the anchor and each retrieve to stop any snagging and my anchor locker is not deep enough to allow the 50m of chain to lay neatly and it piles up beneath the windlass and then snags so I have to sweep it aside on retrieve. The shackle is a two hand job as you say and I will look into the chain hook now-thanks for that . Matter of interest does the chain hook allow for the chain to go straight out on setting it as I have now looked at some pics and it looks like it kinks the chain? .

 

[J Neeves]

Mike,

Chain hooks 'kink' the chain - or the link in the hook is not aligned with the rest of the chain. But there are a number of hook designs and they all 'work' slightly differently. But the chain is not straight, you attach the hook, deploy more chain until you have a 'sag' of chain between bow roller and hook (this extra length of chain helps secure the chain on the hook and provides for the stretch of the snubber). The hooks with the highest reputation are the cast ones. Oddly the greatest complaint of hooks is that they fall off, usually because they have been allowed to drag over the seabed. But removing a hook is simplicity itself, they slide off. If you need to go to the bow anyway (and we like you need to massage the chain in the locker) then removing a hook is not onerous.

The ability to absorb snatch loads is an advantage that, to us, far outweighs any disadvantages of using a snubber - just think of that bungy jumper

There are hooks with locking devices to stop them falling off, Mantus and Witchard come to mind, but they require 2 hands to release.

Mike you could simply keep the set up you have now and add a hook onto the existing shackle.

Jonathan

 

[Hurricane]

I don't think I made it very clear in my post.
My bridle does have a chain hook.
One like this

And answering David's point (Blueglass), the hook does seem to naturally drop off as the windlass winds in.

Sorry if I made it sound/look a bit permanent.

Mike

 

[MedMilo]

Agree with much of what's been said above. I always use a chain hook - once anchored up I go to the bow, attach the hook and pay out another 3-5 meters of chain and then cleat it off. Usually then pay out another couple of metres to create loop of chain previously mentioned. In a strongish wind the chain loop will almost completely disappear as the anchor plait attached to the hook stretches out.

There are three big advantages to this arrangement I think;
1) the anchor plait acts as a spring to reduce the chances of the anchor being snatched out of the seabed
2) you're not relying on the windlass gypsy to hold the weight of a heavy boat, possibly in a strong wind
3) at night it's silent - no grinding of the chain against the anchor roller

In fact I have two of these - one hook spliced to 10m of 12mm plait and one to 10m of 16mm plait. This way I have two levels of 'elasticity' in the event that the wind really picks up!