Anchoring overnight (peacefully)

[NormanS]

I always find these thread more filled with wind than information. The reason, of course, is that each person posts only a fraction of the whole story. If each person fully described their experience, there would probably be very little conflict. Well, maybe some.

* In shallow water (<3M) chain counts for very little. Whether the anchor drags depends on its holding at that scope (ALL anchors loose capacity with reduce ACTUAL scope measured at the bottom, generally about 30-70% by 4:1, but it depends on the design and the soil.)
* In progressively deeper water, the chain start to keep some curve even in strong winds. By 40-50 feet you may lift the rode off the bottom, but if you have respectable scope (>4:1), not that much with all chain.
* Heavier chain only matters in the middle depths; in the shallows it doesn't do enough, and over 40' light chain works too.

So at the end of the day, all of the posters are relating true experiences. I don't know much about anchoring in deep water (never over 15'--it's shallow around here), and I'll bet most posters don't know anything about shallow water (I consider 6-7' normal, and I go as thin as 3-4').

My main though is that anchor selection and rode selection are two separate discussions; the rode should be able to absorb shock and keep the bottom scope >7:1 at all times (measure at the bottom), and the anchor should be able to hold the tension. There are multiple ways of achieving each goal. Adding rode to a crappy anchor or expecting NG to deal with severe uplift and yawing are both mistakes. Solve the problems separately so that each can do its job properly. No single one-size-fits-all, unless you really like to hobby horse.

I think there may be something being lost in translation here. "Two Nations divided by a common language".
Where I live, "scope" simply means the length of chain and/or rope in use, divided by the depth of water. So it has nothing to do with "bottom scope" or "measure at the bottom".

 

[RupertW]

If using an all-chain rode then I would have expected there was an advantage in higher ratios just due to the weight of the chain, is that not true ?

Boo2

Ah you are back to the catenery effect again which will get you into all sorts of discussions between those who have experience and maths and those who just have experience. I guess the question from your post is - "What advantage do you think weight in the rode gives?"

 

[noelex]

If you want to stop worrying use the right amount of chain ratio for the depth. 10 metres is ten times depth, 15 is 8 times, 20 is six times, 30 is three times. What you are aiming for is that the cantenary holds the boat and the anchor is the backup.

The holding power rises as the scope is increased. The gains are very small at large scopes so for practical purposes there is little gain above 8:1-14:1 depending on the depth and whom you believe.

Unfortunately, there is simply no room to use these large scopes in many anchorages. In addition, boats anchored close together need to be anchored at similar scope to avoid collision if there is a wind shift.

Always using 100m of chain in 10m of water ensures the holding is at or very close to its maximum, but this criterion limits the number of usable anchorages and creates problems for nearby boats.

Perhaps the first hurdle to overcome is the fear that the anchor will automatically drag when the chain lifts off the bottom. This is a common fear, but is quite unfounded.

 

[Chris_Robb]

Ah you are back to the catenery effect again which will get you into all sorts of discussions between those who have experience and maths and those who just have experience. I guess the question from your post is - "What advantage do you think weight in the rode gives?"

Advantage of weight in the rode:
1. In lighter winds, slows down swinging and movement of the boat as the wind changes - not an advantage if the boat next is on lighter chain and swings into you.

I cant think of any more advantages.

DIsadvantages
In gusty conditions, the weight of the chain causes the yacht to ride up towards the anchor in a lull, to then move even faster away with the next gust, snubbing the chain.

Why have chain: Schafe resistance - easier to handle and stow on a winch.


Why have rope: Light weight - elastic to absorb shocks

Chain used with a 20 meter snubber (suitable protected against schafe) is therefore a useful compromise.

 

[Kelpie]

In theory, is it possible to have *too much* scope?
If you have a boat which a lot of windage which 'sails' back and forth at anchor, then a longer rode allows her to build up more speed and turn further off the wind. This would translate to increased dynamic loads at the anchor. Just a thought.

 

[Poignard]

If you think your anchorage is unsafe, and there isn't a better one within easy reach, stay awake.

 

[KellysEye]

It seems the majority here don't think the weight of the catenary matters, good luck when anchoring.

 

[prv]

If you think your anchorage is unsafe, and there isn't a better one within easy reach, stay awake.

The problem (which is where the thread started) arises for those who think that every anchorage is unsafe, even if objectively it's perfectly fine.

Pete

 

[RupertW]

It seems the majority here don't think the weight of the catenary matters, good luck when anchoring.

We don't need luck, we have at least some understanding of the different forces involved and make choices on the things that help keep us secure, not imaginary catenery effects under load or excessive scope that just gives a degree or two better angle when the angle is already fine.

 

[RupertW]

Advantage of weight in the rode:
1. In lighter winds, slows down swinging and movement of the boat as the wind changes - not an advantage if the boat next is on lighter chain and swings into you.

I cant think of any more advantages.

DIsadvantages
In gusty conditions, the weight of the chain causes the yacht to ride up towards the anchor in a lull, to then move even faster away with the next gust, snubbing the chain.

Why have chain: Schafe resistance - easier to handle and stow on a winch.


Why have rope: Light weight - elastic to absorb shocks

Chain used with a 20 meter snubber (suitable protected against schafe) is therefore a useful compromise.

Agree with every bit of that and have a similar setup - but usually use a 5-15m snubber rope with thick rubber snubber attached. In extremis the rubber snubber does little and I let our more rope but in most conditions it stretches more easily than the nylon and absorbs lots of minor shocks. We often anchor with just 12-15m chain out so can't use a long snubber.

 

[noelex]

Ah you are back to the catenery effect again which will get you into all sorts of discussions between those who have experience and maths and those who just have experience. I guess the question from your post is - "What advantage do you think weight in the rode gives?"

Weight in the rode does have some positive effects.

Catenary helps the anchor to set and increases the holding power in some very poor substrates and deep anchorages. It also enables a shorter scope to be used in some circumstances.

The problem is that it takes a great deal of chain weight for a minor improvement. Weight that would be much more efficient added to increasing the size of the anchor. There are also some minor negative effects to holding such as reducing the anchor's ability to dive in some circumstances.

 

[RichardS]

It seems the majority here don't think the weight of the catenary matters, good luck when anchoring.

I'd feel as safe in most circumstances on my Rocna if I had floating rope rather than chain.

That's a negative catenary.

Go figure.

Richard

 

[Neeves]

We have an 11.5m cat. We use 14m snubbers (as a bridle), they are attached at the transom, pass though slots on the stanchion bases (as your furling lines do) and then extend beyond the bow - maybe - 4m to a common chain hook. We can extend maybe another 5m, should there be the need as our snubbers terminate in clutches, we have 5m spare, and we can open the clutches and deploy the final 5m

Snubbers effectively replace 'catenary' but 'work' to what ever windspeed for which they are designed. Catenary stops working at a point defined by the amount of chain you carry.

Jonathan

 

[GHA]

It seems the majority here don't think the weight of the catenary matters, good luck when anchoring.

When the forces get up makes very little difference, though there are still a few around who continue to buy into the myth .
Take your head out of the sand and get a good snubber setup, far more effective at reducing forces on the anchor when the wind pipes up .

 

[RupertW]

Weight in the rode does have some positive effects.

Catenary helps the anchor to set and increases the holding power in some very poor substrates and deep anchorages. It also enables a shorter scope to be used in some circumstances.

The problem is that it takes a great deal of chain weight for a minor improvement. Weight that would be much more efficient added to increasing the size of the anchor. There are also some minor negative effects to holding such as reducing the anchor's ability to dive in some circumstances.

Agree with all the above although I don't quite understand the poor substates bit. It certainly helps in crowded anchorages and no wind situations where you genuinely do lie to a vertical chain which slowly wanders around the seabed not around your keel. But as you say the effect is minor and in the wrong place.

The other (minor) catenery effect is a heavy chain dampening the surge forces as it goes from a deep curve to almost straight - but once the wind gets up the curve is so shallow the dampening almost disappears and elasticity of rode becomes the second most important way of avoiding snatching (after reducing the amount the boat veers about).

 

[RupertW]

I'd feel as safe in most circumstances on my Rocna if I had floating rope rather than chain.

That's a negative catenary.

Go figure.

Richard

Same here with a Delta (apart from the worry I'd have about the rope wearing through on some minor seabed obstruction). The only reason I haven't upgraded to a better anchor is the Delta has never dragged once set and one way I sleep well is knowing how familiar gear has worked so many times before. Rocna or Spade on the list though, along with 100m of stainless steel 8mm to replace the 60m of 10mm galvanised.

 

[Chris_Robb]

Same here with a Delta (apart from the worry I'd have about the rope wearing through on some minor seabed obstruction). The only reason I haven't upgraded to a better anchor is the Delta has never dragged once set and one way I sleep well is knowing how familiar gear has worked so many times before. Rocna or Spade on the list though, along with 100m of stainless steel 8mm to replace the 60m of 10mm galvanised.

One thing I have noticed with the Delta, and this was observed when we were stuck in Astypalea for 5 days with a screaming Melteme, that the deltas on two yachts around us, gradually crept in and had to have a meter or so chain taken in every day. Contrast with the Manson Supreme, Rockna and Spade types, they just disappeared below the surface towards Australia. Holding was firm sand.

 

[Neeves]

I'd debate the idea that catenary helps the anchor to set.

The engine is used to set the anchor. If the engine's energy is part focussed at straightening catenary, then it is not being used to set the anchor. Most modern anchors will set at a 5:1 scope - so better with Kryptonite piano wire and all the energy going to setting the anchor (than straightening a 12mm chain rode)?

It a bit like applying your snubber(s) before power setting the anchor - much of the engines energy goes into stretching the snubber - better to tie off to a strong point and then directly setting the anchor. And if the energy does not go into the snubber - then the snubber is not much use.

Jonathan

 

[Neeves]

One thing I have noticed with the Delta, and this was observed when we were stuck in Astypalea for 5 days with a screaming Melteme, that the deltas on two yachts around us, gradually crept in and had to have a meter or so chain taken in every day. Contrast with the Manson Supreme, Rockna and Spade types, they just disappeared below the surface towards Australia. Holding was firm sand.

I did wonder where that Supreme came from

Jonathan

 

[Chris_Robb]

I did wonder where that Supreme came from

Jonathan

At least the built it to the correct specs!:nonchalance: