Anchor Scope

[KellysEye]

>NO SUCH THING AS CATENARY HELPING THE ANCHOR

I've never said it helps the anchor. I have repeatedly said that the weight of the catenary is important to take the load off the anchor which is the backup for when the wind goes right up. At which point let out more chain or put out a second anchor.

>In lighter conditions catenary and a heavy rode (or even a kellet) may reduce snatching and minimise swing - BUT NOT IN EXTREME CONDITIONS. As I've said before - piano wire would perform almost identically (assuming it had sufficient tensile strength).

Do you really think piano wire if strong enough, or as mentioned Dyneema would work as well as chain, if so why do you see no boats using it. In extreme conditions put out a third anchor and make sure it's a monster, ours was a huge Fortress.

 

[GHA]

I'm mulling over whether to install 6mm G7 (still on our Lightwave) as our new anchor chain for our next trip to Tasmania. Putting our money where my mouth is. Its as near to piano wire as I can get

How tidal is it down there? A bit of wind over tide and my boat will point away from the anchor, with the chain disappearing under the boat. Too light chain might end up with it rubbing against the bow for part of each tide, on a long keeled boat anyway. 10mm seems to keep it clear but not by too much.

So many "unforeseen consequences" with boats. That and sailing about the anchorage would put me off a bit but boats at anchor are complex things, intuition may or may not help, so let us know how you get on if you do go for it.

 

[lw395]

....

In strong wind, which is really all we are intersted in ....

I don't think that's true in my case.
Sometimes things like WTF will happen when the tide turns?
And can I find space to anchor, its not going to be windy?

cause me more concern than chucking out a long bit of nylon if it's blowing.

If there's going to be space in Newtown for an 11:1 scope anytime soon, please let me know!

With these real-world constraints, I have often found a kellet very effective.

 

[lw395]

How tidal is it down there? A bit of wind over tide and my boat will point away from the anchor, with the chain disappearing under the boat. ....

Rope can of course be worse than that, and catch on the rudder or keel. I've had that it's not good. A boat held sideways to the tide by the rode being on the keel is a good recipe for dragging.
I really do not want to repeat that particular comedy of errors.
Another good case for a kellet.

 

[Neeves]

Thanks Jonathan. Should I tart it up for CH? Cheers, Andrew

No need to tart it up, but you might want to make it look 'different' - but send it to Phil Ross, definitely

Jonathan

 

[Neeves]

How tidal is it down there? A bit of wind over tide and my boat will point away from the anchor, with the chain disappearing under the boat. Too light chain might end up with it rubbing against the bow for part of each tide, on a long keeled boat anyway. 10mm seems to keep it clear but not by too much.

So many "unforeseen consequences" with boats. That and sailing about the anchorage would put me off a bit but boats at anchor are complex things, intuition may or may not help, so let us know how you get on if you do go for it.

Its a big island! Up north, they have monster tides, I'm not sure of the limits but 11m sticks in my mind, round Mackay they have 7m tides but mostly, Mackay, the water just goes up and down (no current). Further north they have big currents, overfalls and the like. Its not the tides but whether there is any current with it. In Bass Strait they have 3m tides but down the west coast of Tasmania they have 60cm tides - as the 2 are closely connected (at the top left hand corner of Tas) there is an enormous volume of water rushing one way or the other. Last time we made that passage we were making 6 knots through the water and 12 knots over the ground (oddly, in complete silence - like sailing in oil) With our 8mm chain we got stuck outside Smithton and had the conditions you described 35 knot winds a strong tidal flow, chain running straight back under the hulls, took all the AF off. The 8mm was no help, I do not see 6mm being much different - in fact its a bit like the catenary phurphy - you would need maybe 16mm chain before it made any difference under strong tides - so depends on the flow.

Jonathan

 

[Neeves]

One reason people do not use Dyneema is because we tend to be very conservative and are slow to change and adopt new ideas and new technology - especially if it goes against everything we were taught to believe. It does take a long time for people to read, consider and then understand.

Dyneema is relatively new, (25 years in the yacht industry?) it is only now being used in standing rigging, its taken almost 2 decades for it to be realised that it is little affected by UV. Its also expensive and can be cut by coral (or oyster shells on rock) so for those who have wide ranging cruising grounds it is simply not feasible. I suspect that Dyneema would abrade actually in the seabed - that bit of the cord dragged down by the anchor (do not know, merits a look) This is also why many use all chain rodes - good abrasion resistance. For those who can use chain + cordage - nylon is ideal as it gives elasticity.

The reason one does not use piano wire is that it simply is not strong enough and it is only recently galvanised G7 chain has been made available. You will find a surprising number of people have changed from say 12mm G3 or G4 to 10mm G7, or 10mm to 8mm. That fall in chain size still leaves the chain at about the same strength, so 10mm G3 is slightly less strong than 8mm G7. A problem with G7 was, or is, hydrogen embrittllement but Maggi seem to have overcome the issue and there are other moves afoot to remove the issue completely. The advantage of going down in link size are the enormous weight savings which then gives the ability to carry a longer length, opening up deeper anchorages. Other than buying a new gypsy the cost disadvantage is not that great, G7 costs more than G3, or G4, but you do not need the same size link - so its not as expensive as you think. Depends on the locker - but you have less risk of chain towering. Smaller G7 also helps the anchor to set more deeply. But G7 is new, little known - and as mentioned, people take a lot of convincing (having been brought up with the idea of catenary being that answer to a yachtsman's prayer). However even those using G7 are still cautious - the chain is far stronger than ever needed, maybe in 20 years time those using 12mm G3 will move to 8mm G7, softly, softly, catchee monkey?

Jonathan

Edit added: The only people I know (and enough to suggest it is more common than one might think) using smaller sized G7 are those that live on their yachts and/or people taking long cruises where they will anchor in unknown places and thus on varying seabed types, at unpredictable depths and possibly with less useful weather forecasts.

 

[KellysEye]

>The only people I know (and enough to suggest it is more common than one might think) using smaller sized G7 are those that live on their yachts and/or people taking long cruises where they will anchor in unknown places and thus on varying seabed types, at unpredictable depths and possibly with less useful weather forecasts.

Having met well over five hundred long distance cruising boats on our travels I've never met anybody daft enough to downsize anchor chain, or stupid enough to use dyneema or similar which would give a straight line pull on the anchor in 5 knots of wind.

>people taking long cruises where they will anchor in unknown places and thus on varying seabed types, at unpredictable depths and possibly with less useful weather forecasts.

There are no unknown places they are all on a chart and many have a pilot book.There are few sea beds you can't anchor on the three of most common are very soft mud to a considerable depth and thin sand over dead coral that looks like a sand bottom and thick kelp or other thick weed. If we found we couldn't set an anchor in one place we tried other places where in the bay it would set, there are two sand over coral places in English Harbour and behind the reefs in Union island . There are no unpredictable depths all depths are on all charts. Forecasts are easily available everywhere you just need to work out how accurate they are. Most in the Tropics are fine because it's a fairly simple weather system, unlike the north Atlantic

 

[noelex]

There are no unknown places they are all on a chart and many have a pilot book

I am using G7.

I anchor in plenty of places where there are no adequate charts/pilot books. They are usually the best spots.

 

[NormanS]

There are no unknown places they are all on a chart and many have a pilot book.

Ha ha! Maybe you should get out more. Parts of the West Coast of Scotland are charted at 1:200,000. How much detail does that give for anchoring? And then there's the bits that say, "Not Surveyed". I'm not complaining, just saying that some of us find our own anchorages.

 

[Neeves]

Ha ha! Maybe you should get out more. Parts of the West Coast of Scotland are charted at 1:200,000. How much detail does that give for anchoring? And then there's the bits that say, "Not Surveyed". I'm not complaining, just saying that some of us find our own anchorages.

We too have big white patches 'Not Surveyed' and we have other large bits of coastline that have not been surveyed since the original surveys were conducted in the early or mid 1800s.

Jonathan

 

[Andrew G]

KellysEye. I'm having a problem understanding what you mean by the sentence:

". . . I have repeatedly said that the weight of the catenary is important to take the load off the anchor which is the backup for when the wind goes right up . . ."

Are you saying that the chain is providing holding power (for example via friction with the seabed) and that the anchor is a backup to the chain (that is, provides less holding power)?

Could you possibly rephrase it so I can better understand?

Thanks, Andrew.

(Jonathan, thanks and yes I'll send to Phil and yes Mackay has ~7m tides and the Kimberley ~11m (Bay of Fundy, Canada/US has 15m) - I've had to anchor there in 25+m, high current and charts based on those by Matthew Flinders et al - certainly not to the level that others are used to)

 

[Neeves]

Andrew,

The best piece of cartography I know is the Melaleucca Channel in Port Davey (Tasmania). The original was conducted by 3 gifted amateurs in 1953 (I think that is the date) and was done in fathoms, feet and inches. On the swanky new metric chart (which has a lot of those white 'Not Surveyed' pieces) they have used the numerical data but unusually used a conversion factor of 1 Fathom equals 1 metre. As it is not much more than a fathom deep and there are no, or minimal, tides one can only assume the hydrographer wanted to restrict access to multihulls? But it does make one wonder about other pieces of the same and other charts.

Jonathan

 

[Andrew G]

I went up there and then turned to Stbd and then almost to the end of the airfield - came to an ubrupt and noisy halt (I draw 1.8m) - too narrow for you Johnathan - only 10.25m wide. I try to keep clear of hard noisy stuff. (For others, the "channel" is only "deep" for a few meters width and is marked by sticks with beer cans on them - but it is seriously beautiful).
In the Kimberley one island was 200m out of position in a recently surveyed section. I still have an old chart of my Dad's of Port Phillip referencing the survey work done by Mathew Flinders (~1801). But we digress . . . Andrew

 

[KellysEye]

>Are you saying that the chain is providing holding power (for example via friction with the seabed) and that the anchor is a backup to the chain (that is, provides less holding power)?


Yes it is providing holding power but not friction it is the weight of chain in the catenary, if the wind slowly picks up and the boat moves back more chain will rise off the bottom increasing the weight of the catenary. Eventually the catenary will reach the anchor and that's when it's time to do something, as mentioned more chain or a second anchor. If the chain goes straight there is no catenary to hold the boat so you will drag very soon. Hope the explains it.

 

[lustyd]

>Are you saying that the chain is providing holding power (for example via friction with the seabed) and that the anchor is a backup to the chain (that is, provides less holding power)?


Yes it is providing holding power but not friction it is the weight of chain in the catenary, if the wind slowly picks up and the boat moves back more chain will rise off the bottom increasing the weight of the catenary. Eventually the catenary will reach the anchor and that's when it's time to do something, as mentioned more chain or a second anchor. If the chain goes straight there is no catenary to hold the boat so you will drag very soon. Hope the explains it.

So are you saying the anchor doesn't hold the end of the catenary still until all the chain is off the seabed, or are you saying that the catenary reduces the load on the anchor while there is still chain on the seabed? Physics would suggest that either way the anchor won't move if it has the correct holding power and that when the wind gets up the chain is irrelevant anyway so why keep mentioing it?

 

[akyaka]

I'm a simple soul. If I just lay my anchor and leave it ,sometimes with even a small amount of current and/or wind the boat will drag its anchor. If I in the same conditions and with the same length of chain I anchor and dig in until the bow pecks I do not drag even when the wind picks up . Whats holding me ?

 

[Neeves]

I'm a simple soul. If I just lay my anchor and leave it ,sometimes with even a small amount of current and/or wind the boat will drag its anchor. If I in the same conditions and with the same length of chain I anchor and dig in until the bow pecks I do not drag even when the wind picks up . Whats holding me ?

I do not think you understand Kelly'sEye, maybe he should explain again in more simple English. His is a very complex subject and would merit and enjoy some further elaboration, maybe quantification and some maths would help.

Jonathan

 

[akyaka]

I do not think you understand Kelly'sEye, maybe he should explain again in more simple English. His is a very complex subject and would merit and enjoy some further elaboration, maybe quantification and some maths would help.

Jonathan

Actually I think I do, it just doesn't seem to fit reality, the chain does not go "bar tight" before the boat drags in the same way that it does when there is a blow and the anchor is dug in and holds me.

 

[KellysEye]

>So are you saying the anchor doesn't hold the end of the catenary still until all the chain is off the seabed, or are you saying that the catenary reduces the load on the anchor while there is still chain on the seabed? Physics would suggest that either way the anchor won't move if it has the correct holding power and that when the wind gets up the chain is irrelevant anyway so why keep mentioing it?

The catenary is the curve in the chain before the chain lying on the bottom, there is no pull load on the anchor when there is still chain on the bottom. How can chain be irrelevant? Trust me boat anchors do move I've seen many boats drag and two on the rocks when the wind gets up because they have put too little chain or don't carry enough for strong winds or haven't put out a second anchor out.

>the chain does not go "bar tight" before the boat drags in the same way that it does when there is a blow and the anchor is dug in and holds me.

All the boats I've seen drag have had bar tight chain.