Letting out too much anchor chain

[KevB]

Why? Surely each boat will be affected by wind and tide in the same way irrespective how how much chain is out. How can the amount of chain on the bottom influence which way your boat faces?

Ok. Get thinish piece of rope about 4' long and twirl about a foot of it around in a circle. rope stays stays straight and easy to twirl. now hold it at the end so your twirling 4' of rope. not so easy to twirl and the rope has a bend in it as you twirl with the ends no longer facing the same way.
Boats with the correct amount of chain will drag the chain along the sea bed at the anchore so generally the chain is fairly straight. A boat with too much chain will drag the chain in an arc and as the boat pulls against the arc it acts like an elastic band making the boat pivot backwards and forwards. You see it all the time.

25mtrs of chain in 4mtrs of water is a silly amount of chain. Ok if you're the only boat around but irresponsible and a bit ignorant in popular anchorages.

 

[henryf]

I'm not sure I quite follow the rope twirling bit but never mind.

In many places such as Newtown Creek we don't have the luxury of acres of free space. The anchor generally digs in well enough, mud is sticky stuff. So we need to limit how far we travel from the anchor. To make matters worse there are some funny currents which combined with a mix of motor and sailing boats can lead to craft facing in all directions.

We allow for the height of the anchor roller above water and use the 4 times rule.

So getting back to the length of chain affecting how you lay. You are never pulling directly on your anchor. The chain always drops vertically to chain on the bottom which does the bulk of the work and flattens out the pull on the anchor so it's parallel to the sea bed, thus causing the anchor to dig in as it gets yanked.

Any swinging from side to side on a single anchor is surely the wind pushing you off the natural direction of the current. Flatter hulls with less keel will be influenced more. A sailing boat with a deep keel will be held by the current more and influenced less by the wind.

Henry

 

[jfm]

Ok. Get thinish piece of rope about 4' long and twirl about a foot of it around in a circle. rope stays stays straight and easy to twirl. now hold it at the end so your twirling 4' of rope. not so easy to twirl and the rope has a bend in it as you twirl with the ends no longer facing the same way.
Boats with the correct amount of chain will drag the chain along the sea bed at the anchore so generally the chain is fairly straight. A boat with too much chain will drag the chain in an arc and as the boat pulls against the arc it acts like an elastic band making the boat pivot backwards and forwards. You see it all the time.

25mtrs of chain in 4mtrs of water is a silly amount of chain. Ok if you're the only boat around but irresponsible and a bit ignorant in popular anchorages.

nice lake sailor but I don't agree. I totally don't get the rope twirl story.

 

[asteven221]

I always read anchor threads with much interest as it's not something I am particularly comfortable with - especially overnight. However I have anchored plenty of times without mishap, so whatever I am doing seems to work.

Anyway whether it's on here or scuttlebutt, anchor threads are always looooong with many contributors and words of wisdom, claims and counterclaims. It makes for enjoyable reading.

However I can't help concluding that given so many differing opinions on what's deemed "the right way" - the vast majority of us don't actually know much about anchoring, the science behind it and in particular what's actually going on down in the seabed. Do we just overcomplicate what is really a fairly simple procedure?

I suspect that loads of people just get on with it and anchor successfully all the time without any drama!

 

[DAKA]

25mtrs of chain in 4mtrs of water is a silly amount of chain. Ok if you're the only boat around but irresponsible and a bit ignorant in popular anchorages.

Kev, I dont even want to start on the twirly chain thingy but feel I must protest regarding your claims of ignorance for 25m chain in 4 m of water.

Lets choose East head being about as popular as you get in the solent.

if you go in at lowish tide 4m you need to allow for a 2 m rise on a neap and over 3m rise on a spring, add this to your 4m water = 6 to 7 meters x 4 = 24 to 28 meters of chain (plus bow height) , I often sit on the beach with a BBQ and like to watch my boat but I seldom return unless we need more Ice, I wouldnt plan to keep going back and letting more chain out as the tide rises and haul it back up each hour if falls again.

Will you agree to qualify your ignorant comment with highest water expected of 4m or do you really think mariners are being ignorant letting the right amount of chain down.

NB, I chose East head deliberately as a current whips through , I think you may have a point on calm days in sheltered anchorages.

 

[Nick_H]

Ok. Get thinish piece of rope about 4' long and twirl about a foot of it around in a circle. rope stays stays straight and easy to twirl. now hold it at the end so your twirling 4' of rope. not so easy to twirl and the rope has a bend in it as you twirl with the ends no longer facing the same way.
Boats with the correct amount of chain will drag the chain along the sea bed at the anchore so generally the chain is fairly straight. A boat with too much chain will drag the chain in an arc and as the boat pulls against the arc it acts like an elastic band making the boat pivot backwards and forwards. You see it all the time.

25mtrs of chain in 4mtrs of water is a silly amount of chain. Ok if you're the only boat around but irresponsible and a bit ignorant in popular anchorages.

Any chain that doesn't lift off the seabed as the boat pulls and yaws in the wind is irrelevant. Doesn't matter if it's a metre long or a hundred metres, or whether it runs straight to the anchor or has a 90 deg dog leg. The boat will lie at anchor as if the chain were bolted to the seabed at the nearest point to the boat where the chain doesn't lift, so letting out too much chain makes no difference to the angle the boat lies.

 

[MapisM]

totally don't get the rope twirl story.

+1.

Question for KevB: would you agree that in a proper anchorage, you should always have some of the chain attached to the anchor laying on the seabed and not moving at all?
If you do, just think about the geometry of the movements involved and you'll easily see that the dynamic of the "moving" part of the chain, its angle, arc, etc. is exactly the same, regardless of whether the "non moving" bit is one or one hundred meters long.
If otoh your opinion is that it's ok if the whole chain moves around, to the point that often only the anchor actually holds the boat, then I would agree that the boat movement can be different and more "limited", so to speak. But till when, it's anybody's guess.
Fine for short stays in fair weather with somebody on watch, maybe. In fact, I recently mentioned in another thread an anchorage spot where I usually deploy chain length just about twice the depth, due to restricted space.
But if you think an anchorage is safe for overnighting, leaving the boat unattended, etc. with 12m of chain in 3m of water, I have two words for you: good luck.

 

[gjgm]

Any chain that doesn't lift off the seabed as the boat pulls and yaws in the wind is irrelevant. Doesn't matter if it's a metre long or a hundred metres, or whether it runs straight to the anchor or has a 90 deg dog leg. The boat will lie at anchor as if the chain were bolted to the seabed at the nearest point to the boat where the chain doesn't lift, so letting out too much chain makes no difference to the angle the boat lies.

If the "excess" chain is stable, yes,but what if the excess chain on the seabed in an arc moves? Instead of having a fixed point to the seabed, you now have a roving point to the seabed. I suppose it is possible that the boat doesnt then lie in a constant direction , (not discussing location) while the chain moves?
If you have your perfect setting with wind to north, the boat holds like that, effected , lets say, only by the wind. If you have a huge arc of chain, you initially lie in the same north direction, but if you break the chain off the sea bed, do you not now have the pull of the wind and a new pull of the moving chain?

 

[PEJ]

These last few posts are at the heart of my question.

If I drop 25m of chain will I spin around in a 25m circle? I think Nick_H is saying no to this.

I would spin around the last horizontal part of the chain so I could spin 180 degrees and be lying on top of my anchor?

But in a busy anchorage if I let out a lot of chain it could come to pass that a boat is lying on my side of my anchor so when I go to pull it up that boat could be between me and my anchor point.

 

[Nick_H]

If the "excess" chain is stable, yes,but what if the excess chain on the seabed in an arc moves? Instead of having a fixed point to the seabed, you now have a roving point to the seabed. I suppose it is possible that the boat doesnt then lie in a constant direction , (not discussing location) while the chain moves?

Well that could happen on a single pull of the chain on the strongest gust of wind, but the chain that had moved wouldn't return to its original (arced) position afterwards, it would lay straight to the boat, and the boat would then lie at anchor in the same orientation as all the other boats.

 

[gjgm]

Well that could happen on a single pull of the chain on the strongest gust of wind, but the chain that had moved wouldn't return to its original (arced) position afterwards, it would lay straight to the boat, and the boat would then lie at anchor in the same orientation as all the other boats.

Yep, I agree with you.. for the boat not to do so would need a very mobile chain as far as I can see, undersized chain for example?
I was just wondering what could cause Kevb's supposition....

 

[gjgm]

These last few posts are at the heart of my question.

If I drop 25m of chain will I spin around in a 25m circle? I think Nick_H is saying no to this.

I would spin around the last horizontal part of the chain so I could spin 180 degrees and be lying on top of my anchor?

QUOTE]
Doesnt that suppose that your chain is so heavy that in fact you dont need an anchor on the end of it ?
Surely in the perfect set, the chain holds the anchor flat to the sea bed and further towards the boat the "right length" absorbs some of the movement, but the concept is the chain should be in a straight line to the anchor? So, can too much chain prevent that, right?

 

[noelex]

These last few posts are at the heart of my question.

If I drop 25m of chain will I spin around in a 25m circle? I think Nick_H is saying no to this.

In a moderate wind your stern will swing with a radius of approximately your chain length + the length of your boat.
So if a moderate wind changes direction by 180 degrees your stern will move approximately 50m +2xthe length of your boat.

At lower wind strengthen you may pivot about your bow, or something in between. (Dragging some of the chain in the new direction)

The wind strength where the boat will not be held by the chain, varies on a number of factors but 20 knots is ball park.

So if a 20k wind changes direction 180 degrees expect your stern to be about 70m from where it started. (With 25m chain)

 

[Philiz]

Ok. Get thinish piece of rope about 4' long and twirl about a foot of it around in a circle. rope stays stays straight and easy to twirl. now hold it at the end so your twirling 4' of rope. not so easy to twirl and the rope has a bend in it as you twirl with the ends no longer facing the same way.
Boats with the correct amount of chain will drag the chain along the sea bed at the anchore so generally the chain is fairly straight. A boat with too much chain will drag the chain in an arc and as the boat pulls against the arc it acts like an elastic band making the boat pivot backwards and forwards. You see it all the time.

25mtrs of chain in 4mtrs of water is a silly amount of chain. Ok if you're the only boat around but irresponsible and a bit ignorant in popular anchorages.

No. I don't get it, as other have said the boat will lie off the point where the chain leaves the bottom, can't see how the length of chain between that point and the anchor can influence which way the boat points. Yes, you see boats pointing in different directions in the same anchorage, but IMHO that is due to different influences from wind and currents acting on different hull types.

25 metres of chain in 4 mtrs of water aint silly, there are situations where it's absolutely essential.

 

[noelex]

As others have said the direction a boat points when anchored is related to above and underwater profile combined with the relative influence of wind and current.
It is not related to amount of chain out (unless the boat is dragging)

 

[oceanfroggie]

Its only a problem insomuch as you might swing into other boats nearby if they are lying to a shorter length of chain. If it was a relatively calm day and I was staying on board all the time, I'd be happy with 5 x depth ie 15m but make sure the anchor is dug in. If I was going ashore for lunch, then I'd definitely want 20-25m out and be sure that there was plenty of swinging room. Of course you will never stop some numpty dropping his hook right next to you but if your boat swings into him, its his problem. Just put some fenders out

+1

Agree 4:1 is not enough. Generally depending on conditions we usually leave out 7:1 (eg 20-25m in 3m) for overnight, or more if there is a strong breeze and a bit of chop. Even in an F5-6 anchored in in the lee of an island she has yet to drag with 30+m out.

 

[oceanfroggie]

The water temp has only just risen above freezing

The water temp here on Irish coast is a record 20deg!!! Usually it's late August before it gets into the mid teens of a hot spell.