noelex
Well-Known Member
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Anchor wally
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dom
Well-Known Member
Someone needs to explain this to the anchors. They often don't understand.
That's a very posh chain you have there nolex
noelex
Well-Known Member
That's a very posh chain you have there nolex
Sadly it is not my anchor. I shudder to think what the stainless chain and Ultra anchor is worth.
When I dive maybe I should take bolt cutters instead of a camera
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JumbleDuck
Well-Known Member
Sadly it is not my anchor. I shudder to think what the stainless chain and Ultra anchor is worth.
When I dive maybe I should take bolt cutters instead of a camera
Be sure to take a camera and telephoto lens to record the reaction when a manky old plough copy and some rusty chain emerge from the sea ...
GHA
Well-Known Member
5 to one works fine day to day and it's what I tend to go for in shallower water , it just doesn't reflect what's actually happening with the catinery. Check the graph out, it mirrors the catinery equation well even down to shallow depths, bearing in mind it's showing the scope which would just lift the last link of an10mm chain with 230kg horizontal load, not what might make more sense in the real world. And for 30m that's a scope of 2.74:1.
Assuming the catinery equation is correct on the graph , feel free to check, anyone
Edit. This site has it coming out at about just over 90m chain in your example, 31m to bow roller.
http://www.spaceagecontrol.com/calccabm.htm?F=2300&a=167&q=2&g=9.81&Submit+Button=Calculate
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skipmac
Well-Known Member
Please, let us not get sloppy with the math. I calculated originally 2.7419354839. Those last few mm can be very critical in 30M of water. :encouragement:
Meanwhile, back in the real world, all these formulas and catenary tables are fine in moderate conditions but I've been anchored a couple of times with strong winds and swell that stretched the chain pretty much straight. Then formulas go out the window.
And in 30 + 1 M with chain and the weight of that much chain I would go with 90M and a 3/1 scope most of the time but would want more in very high winds. Of course I only have about 60M of chain so the whole point is moot. :nonchalance: Guess I can only anchor in water 20M or less and in moderate to calm conditions. OR add a big chunk of rope to the bitter end of the chain.
sarabande
Well-Known Member
Someone needs to explain this to the anchors. They often don't understand
The chain and the spine of the anchor are not in a straight line. I suspect there is no real tension in that setup.
oldbilbo
...
Absolutely! It's Photoshopped....!
No-one, but no-one, actually uses a shiny stainless steel anchor with some shiny stainless chain to deploy it into a dirty seabed.
Everyone knows such 'bling' is only for show, along the marina pontoons, and mustn't be abraded by any suggestion of actual use in a manky marine milieu....
NormanS
Well-Known Member
And the chain appears to have a reverse catenary!
noelex
Well-Known Member
It does look in this photo like there is some reverse catenary. Most of the underwater photos are taken on a wide angle setting and the lens has little bit of distortion.
In real life in the gusts it looked in a dead straight line all the way to the boat. Mathematically, of course there is always some catenary, but in practice this is minimal with stronger wind.
Here is a shot of the same anchor from the side:
This is another example. This one is a Rocna.(In tandem, but the other anchor was doing nothing) Rocna owners are too cheap to use shiny chain
:
I guess the point is that it does not take a lot of wind or tension before the catenary effectively disappears, especially in the gusts, as was occurring here. When this happens the chain is essentially a straight line to the boat. Not only does this lift the chain, but as the boat swings or yaws around the mean position, the chain will not be in line with the shank. With a well set anchor the shank will remain steady as the boat swings around. The shank does not yaw around from side to side with each gust and the photo illustrates this.
I hope the photos give people some idea what is really happening to their anchor and chain on the bottom. In these particular photos taken recently, the wind was only moderate, the scope was not great, and the catenary was only disappearing in the gusts, but people put too much faith in catenary. The reality is that in most cases where the anchor is at risk of dragging, the catenary will have effectively disappeared. The notion that the anchor will drag as soon as the catenary is lost and the chain lifts off the bottom, is wrong.
None of my photos have been manipulated in any way other than simple changes to exposure, contrast etc. I am always happy to show the original image direct from the camera without any adjustments whatsoever. This is the original of the Ultra photo direct from the camera card. You can see it is almost identical:
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JumbleDuck
Well-Known Member
Here is a shot of the same anchor from the side:
A nice picture, showing that the chain is pointing at the flukes, as you'd expect.
IanJackson
Well-Known Member
Anchoring is a fascinating thing to watch. I'd be interested to know if there is a con ensues amongst UK yachties as to the best method of anchoring. Briefly I line the boat up into wind, go astern slowly and try to lay out the appropriate amount of cable/chain until (usually) the anchor bites and the boat stops. If I suspect soft mud I'll wait a few moments for the anchor to sink into the mud before going astern to bed it in tight. This usually works with my delta and I do this if mooring stern to Greek style.
That said I watch numerous Italians, French, Spanish etc. here in the Med dropping their anchors while going ahead thus driving over the cable, then letting the boat drift back with the wind often sideways until they 'feel" the anchor must be OK. I wonder is this how they are taught in the Med?
That said I watch numerous Italians, French, Spanish etc. here in the Med dropping their anchors while going ahead thus driving over the cable, then letting the boat drift back with the wind often sideways until they 'feel" the anchor must be OK. I wonder is this how they are taught in the Med?
NormanS
Well-Known Member
With a SAILING boat, the latter approach makes a lot of sense.
macd
Well-Known Member
Must be one of them new-fangled lithium chains, then, because something's keeping it off the bottom.
ghostlymoron
Well-Known Member
When anchoring under sail, you should approach downwind at moderate speed. The anchor and warp will then be orientated in the correct direction, the boat will swing round to the wind when the anchor bites.
JumbleDuck
Well-Known Member
That's what I generally do - I call it the "handbrake turn" method of anchoring.
NormanS
Well-Known Member
PaulRainbow
Well-Known Member
30metres, and lots of rope.
ghostlymoron
Well-Known Member
I'm glad someone else is keeping the skills of 'cruising under sail' alive. Too much reliance on engines these days............fnaa, fnaa
oldbilbo
...
Quite a few years back, we had to beat up to Port Ellen ( south-east corner of Islay ) in a building gale and gathering dark. The engine on this Rival 34 - or at least, the hydraulic gearbox - had died on us and PE was the nearest haven. We had only the harbour diagram in Reed's....
It was a black night, blowing hard. We eventually felt our way up to the windward, NW corner, then beam-reached slowly back and forwards in about 3 metres of water under reefed main, while laying out 30 metres of chain on deck and snubbing it off on the solid Samson post. Making abut 2 knots, we dropped the hook. While letting the chain run out, I put the helm up, t'other half dropped the mainsail into the lazy-jacks, and the boat described a steady half-circle downwind - until the progressive pull on the chain brought her bows firmly around, head to wind, stopped.
Kettle on.
Anchor watch.
Very securely 'hooked'....
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