steveallan
Well-Known Member
Well done on raising the 'R' word 'Rocna' /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif
Second anchor
- Thread starter HoratioHB
- Start date
binch
Well-Known Member
The trouble with testing anchors is that linear pull is NOT a reliable measure. When the Admiralty built a new generation of non-magnetic mine-sweepers (circa 1958), they wanted a new design and/or type of anchor of non-ferrous material. I had the task of testing them and started in the obvious way. Each of several different models was set in, and then the pull was steadily incresed until the anchor broke out or broke up (both these happened.) We measured the linear pull and it varied quite a bit. One anchor took almost three times the stran of the worst.
BUT. When we tried the anchors on similar test vessels in storm conditions, the anchor with the best linear pull figure was the first to drag. In fact all the anchors gave almost random results when compared with the linear pull figures. One held well in a steady strong wind but couldn't cope with short gusts because the sudden strain had more unsettling effect than a steady strain.
The critical factor in all anchors was the amount that vessels sheered up either side of the anchor, often carrying their way forward until they were to windward of the anchor.
We went back to the drawing board and tested chain cable instead. The critical factor in holding was the weight of the cable and the length of the links. (these cables were made of bronze).
Nylon anchor cables were only effective if there was an angel weighing about half the anchor weight and about one depth away from the anchor. (This was in very strong winds).
Finally I tried (as a sort of control and partly as fun) lowering a 1 cwt weight to the bottom instad of the 120lb anchor. With a good scope of cable (don't remember the figure, but say 10 x depth) this held just as well as the anchor.
Finally, let me describe riding to asingle anchor in the Riveer Danube when there was a seven knot current flowing, measured on the log. We rode peacefully, the vessel moving hardly at all.
Now to drive that boat at 7 knots in smooth water needed 35,000 watts of energy.
Measuring the boat's frontal windage by the approximate method (Half the mast-height x the boat's beam we find that to develop force on the boat of 35,000 watts would need a wind of 82 knots, say force 12.
No way would that anchor, our number two bower, have held the ship in such a wind. Ergo, the critical factor is the matter of a steady pull. Anything you can do to prevent the vessel sheering about either side is effort well spent.
And after all that, they didn't build the ships, but I learned a lot at the taxpayer's expense. And one of those things that I learned was that no gear is ever perfect for all the conditions a seaman may encounter, and it is in assessing the conditions and adjusting the gear to suit that you have the opportunity to use real seamanship, and there is nothing one ever does in a boat that can beat that.
Sorry for the lecture; put it down to old age.
BUT. When we tried the anchors on similar test vessels in storm conditions, the anchor with the best linear pull figure was the first to drag. In fact all the anchors gave almost random results when compared with the linear pull figures. One held well in a steady strong wind but couldn't cope with short gusts because the sudden strain had more unsettling effect than a steady strain.
The critical factor in all anchors was the amount that vessels sheered up either side of the anchor, often carrying their way forward until they were to windward of the anchor.
We went back to the drawing board and tested chain cable instead. The critical factor in holding was the weight of the cable and the length of the links. (these cables were made of bronze).
Nylon anchor cables were only effective if there was an angel weighing about half the anchor weight and about one depth away from the anchor. (This was in very strong winds).
Finally I tried (as a sort of control and partly as fun) lowering a 1 cwt weight to the bottom instad of the 120lb anchor. With a good scope of cable (don't remember the figure, but say 10 x depth) this held just as well as the anchor.
Finally, let me describe riding to asingle anchor in the Riveer Danube when there was a seven knot current flowing, measured on the log. We rode peacefully, the vessel moving hardly at all.
Now to drive that boat at 7 knots in smooth water needed 35,000 watts of energy.
Measuring the boat's frontal windage by the approximate method (Half the mast-height x the boat's beam we find that to develop force on the boat of 35,000 watts would need a wind of 82 knots, say force 12.
No way would that anchor, our number two bower, have held the ship in such a wind. Ergo, the critical factor is the matter of a steady pull. Anything you can do to prevent the vessel sheering about either side is effort well spent.
And after all that, they didn't build the ships, but I learned a lot at the taxpayer's expense. And one of those things that I learned was that no gear is ever perfect for all the conditions a seaman may encounter, and it is in assessing the conditions and adjusting the gear to suit that you have the opportunity to use real seamanship, and there is nothing one ever does in a boat that can beat that.
Sorry for the lecture; put it down to old age.
noelex
Well-Known Member
[ QUOTE ]
Finally, let me describe riding to asingle anchor in the Riveer Danube when there was a seven knot current flowing, measured on the log. We rode peacefully, the vessel moving hardly at all.
Now to drive that boat at 7 knots in smooth water needed 35,000 watts of energy.
Measuring the boat's frontal windage by the approximate method (Half the mast-height x the boat's beam we find that to develop force on the boat of 35,000 watts would need a wind of 82 knots, say force 12.
[/ QUOTE ]
Unless you are driving a small boat over hull speed those calculations don’t seem to be correct.
The excellent examination of rode forces at
http://alain.fraysse.free.fr/sail/rode/forces/forces.htm
puts the force (on a 33 foot waterline vessel) of a 6K current as equal to a 20K wind and a 7 knot current as equal to a 30K wind.
I share your concern about minimizing the effect of sheering/yawing, but yachts just don’t behave with anything like the amount of sheering you were describing.
[ QUOTE ]
The critical factor in all anchors was the amount that vessels sheered up either side of the anchor, often carrying their way forward until they were to windward of the anchor.
[/ QUOTE ]
I have never seen a yacht sheering enough to be close to lying windward of the anchor.
[ QUOTE ]
lowering a 1 cwt weight to the bottom instad of the 120lb anchor. With a good scope of cable (don't remember the figure, but say 10 x depth) this held just as well as the anchor.
[/ QUOTE ]
I am afraid my brain is metric. I can cope with LB etc, but according to google 1cwt is 112lb.. Now I know my old plough was bad, but not this bad.
Finally, let me describe riding to asingle anchor in the Riveer Danube when there was a seven knot current flowing, measured on the log. We rode peacefully, the vessel moving hardly at all.
Now to drive that boat at 7 knots in smooth water needed 35,000 watts of energy.
Measuring the boat's frontal windage by the approximate method (Half the mast-height x the boat's beam we find that to develop force on the boat of 35,000 watts would need a wind of 82 knots, say force 12.
[/ QUOTE ]
Unless you are driving a small boat over hull speed those calculations don’t seem to be correct.
The excellent examination of rode forces at
http://alain.fraysse.free.fr/sail/rode/forces/forces.htm
puts the force (on a 33 foot waterline vessel) of a 6K current as equal to a 20K wind and a 7 knot current as equal to a 30K wind.
I share your concern about minimizing the effect of sheering/yawing, but yachts just don’t behave with anything like the amount of sheering you were describing.
[ QUOTE ]
The critical factor in all anchors was the amount that vessels sheered up either side of the anchor, often carrying their way forward until they were to windward of the anchor.
[/ QUOTE ]
I have never seen a yacht sheering enough to be close to lying windward of the anchor.
[ QUOTE ]
lowering a 1 cwt weight to the bottom instad of the 120lb anchor. With a good scope of cable (don't remember the figure, but say 10 x depth) this held just as well as the anchor.
[/ QUOTE ]
I am afraid my brain is metric. I can cope with LB etc, but according to google 1cwt is 112lb.. Now I know my old plough was bad, but not this bad.
BurnitBlue
Well-Known Member
Good lecture no need to apologise.
I agree about the shearing of the boat causing more "break outs" than a direct pull but had never read of any tests to confirm that conclusion until your post. Thanks for posting in such detail.
I agree about the shearing of the boat causing more "break outs" than a direct pull but had never read of any tests to confirm that conclusion until your post. Thanks for posting in such detail.
A
Anonymous
Guest
For the same reasons in the Med I changed my Bruce for a Delta as the Rocna wouldn't fit. The Delta has been good but when I dive on the anchor sometimes I find that it can't get through the hard sand. Spain and the Balearics have been the worst for us; from Agde all along the coast to Elba we had no trouble at all, over nearly four months. We do take shelter in harbours or marinas strong winds, though, whenever possible.
Bajansailor
Well-Known Member
Just a thought - you had said "Now to drive that boat at 7 knots in smooth water needed 35,000 watts of energy".
Is this 35 kw at the propeller driving the vessel, or is 35 kw the rated power of the engine?
If it is the rated power of the engine, then the power developed at the propeller is probably only about half this amount, ie about 18 kw, due to propulsion efficiency losses.
Is this 35 kw at the propeller driving the vessel, or is 35 kw the rated power of the engine?
If it is the rated power of the engine, then the power developed at the propeller is probably only about half this amount, ie about 18 kw, due to propulsion efficiency losses.
binch
Well-Known Member
The formula used for calculation of wind force effect on a boat is the standard one used by the RIN. I haven'tthe details to hand as I am not at home for Christmas. If I were then I would not be on line. The kilowattage is classed as propulsive effort at the point of application.
I have frequently observed a yacht moving to windward of her anchor. Not directly to windward of course, but on one or other wing of the sheer. To be sure of this one should anchor with an anchor buoy with exactly the right scope n the buoy-rope. This is a prudent precaution if anchored in strong winds.
I enjoy being at anchor. We were once 410 successive nights at single anchor in the Med. It is rare to be disturbed, but it does happen. I sailed then an 87 foot schooner. We had three anchors: No1 bower was 100 kilos. No 2 was 150 kilos and the sheet anchor was 200 kilos. All the anchors were Hall's pattern.
Before that we lived in a ketch of 55 feet with two 75 pound CQRs each on 240 feet of 7/16" chain. We cruised over 50,000 miles and never dragged once.
It is difficult to cruise the Med, especially in winter without having the occasional anchor problem. Often one is a bit hemmed in, but more difficult are the anchorages where one can be surprised by sudden katabatic winds of extreme but short-lived violence.
I aapologise to those incapable of understanding traditional nautical measurements. Note that even the French navy use "une brasse" as a standard. It is a fathom. Also a French measuring tape used for barge building had a mark at every 14 inches, the traditonal spacing for frames. And a French carpenters tape had markings at 16 inches, the stndard spacing for roof rafters. I bought one recently; the markings are still there.
Question: how many kilos to a katlo?
I have frequently observed a yacht moving to windward of her anchor. Not directly to windward of course, but on one or other wing of the sheer. To be sure of this one should anchor with an anchor buoy with exactly the right scope n the buoy-rope. This is a prudent precaution if anchored in strong winds.
I enjoy being at anchor. We were once 410 successive nights at single anchor in the Med. It is rare to be disturbed, but it does happen. I sailed then an 87 foot schooner. We had three anchors: No1 bower was 100 kilos. No 2 was 150 kilos and the sheet anchor was 200 kilos. All the anchors were Hall's pattern.
Before that we lived in a ketch of 55 feet with two 75 pound CQRs each on 240 feet of 7/16" chain. We cruised over 50,000 miles and never dragged once.
It is difficult to cruise the Med, especially in winter without having the occasional anchor problem. Often one is a bit hemmed in, but more difficult are the anchorages where one can be surprised by sudden katabatic winds of extreme but short-lived violence.
I aapologise to those incapable of understanding traditional nautical measurements. Note that even the French navy use "une brasse" as a standard. It is a fathom. Also a French measuring tape used for barge building had a mark at every 14 inches, the traditonal spacing for frames. And a French carpenters tape had markings at 16 inches, the stndard spacing for roof rafters. I bought one recently; the markings are still there.
Question: how many kilos to a katlo?
damo
Well-Known Member
"Good lecture no need to apologise."
I agree - interesting stuff /forums/images/graemlins/smile.gif
I agree - interesting stuff /forums/images/graemlins/smile.gif
NormanS
Well-Known Member
On my 36ft ketch, my main anchor is a 20kg Bruce on 10mm chain. If putting out a second anchor, it is laid well out (to starboard). The second anchor, either a 20kg Danforth or a 20kg fisherman, depending on the type of bottom, has about 6m of 12mm chain, and then nylon warp. I always connect a tripping line and buoy to it. It means that if something happens, like someone dragging down onto me, I can slip the second anchor immediately, and then have only the main anchor to heave in. I can always retrieve the second anchor later. The nylon warp sinks, so isn't a hazard to the prop.
TQA
Well-Known Member
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Spent 7 years living on the hook mostly in the Caribbean and East coast USA in a heavy 38 foot ketch. During that time I used a 45 lb CQR on chain. At times I needed to move and re-anchor. It was so much simpler to just pull up one, motor over and drop it in the new spot. Watching the chinese fire drill with people who had two out getting both back on board and reset was gave hours of amusement.
The only time I would set two would be where there was a strong reversing current [ Like Nassau ] when the second was a 35lb danforth set at 180 degrees.
I am heading out again next year and will set the boat up with that combination.
The only time I would set two would be where there was a strong reversing current [ Like Nassau ] when the second was a 35lb danforth set at 180 degrees.
I am heading out again next year and will set the boat up with that combination.
charles_reed
Well-Known Member
To add to pud\'s post
Agree with many of the things you've said:-
However 1 or 2 points:-
<<Classicly,(sic) veer about 10 times the depth on the bower and then, when just to one side of the wind line let go the second bower with 4 times the depth of chain on it. The second anchor will inhibit sheering about.>>
How many have that much chain? Especially with modern lightweights it would be a physical impossibility to stow (assuming 10m depth) 140m of chain?
An option which I've found works extremely well (and mine is a lightweight fin keel which is appalling at sheering around and sailing up to the anchor) is to dig in @ 5:1 or more, on chain, then attach a textile rode at about 1/2 depth and leave sufficient bight of chain to touch the bottom. That cuts out all sheering and even seems to be an improvement on two anchors at an angle.
Agree with many of the things you've said:-
However 1 or 2 points:-
<<Classicly,(sic) veer about 10 times the depth on the bower and then, when just to one side of the wind line let go the second bower with 4 times the depth of chain on it. The second anchor will inhibit sheering about.>>
How many have that much chain? Especially with modern lightweights it would be a physical impossibility to stow (assuming 10m depth) 140m of chain?
An option which I've found works extremely well (and mine is a lightweight fin keel which is appalling at sheering around and sailing up to the anchor) is to dig in @ 5:1 or more, on chain, then attach a textile rode at about 1/2 depth and leave sufficient bight of chain to touch the bottom. That cuts out all sheering and even seems to be an improvement on two anchors at an angle.
charles_reed
Well-Known Member
<<Unless you are driving a small boat over hull speed those calculations don’t seem to be correct.
The excellent examination of rode forces at
http://alain.fraysse.free.fr/sail/rode/forces/forces.htm
puts the force (on a 33 foot waterline vessel) of a 6K current as equal to a 20K wind and a 7 knot current as equal to a 30K wind.
I share your concern about minimizing the effect of sheering/yawing, but yachts just don’t behave with anything like the amount of sheering you were describing. >>
Quoting Fraysse out of context is, being kind, an unwise move, especially in view of the caveats he puts on the spreadsheet.
You have ignored two other possibilities:- 1. that the boat which was the subject of Pud's calcs may have had a considerable wetted area (such as a long-keeler with a bluff bow) and 2. you are totally inaccurate in the second statement, I have experienced such sheering in the Med where the rules are that winds both gust by 2-3 forces and vary by 45-60 degrees.
The excellent examination of rode forces at
http://alain.fraysse.free.fr/sail/rode/forces/forces.htm
puts the force (on a 33 foot waterline vessel) of a 6K current as equal to a 20K wind and a 7 knot current as equal to a 30K wind.
I share your concern about minimizing the effect of sheering/yawing, but yachts just don’t behave with anything like the amount of sheering you were describing. >>
Quoting Fraysse out of context is, being kind, an unwise move, especially in view of the caveats he puts on the spreadsheet.
You have ignored two other possibilities:- 1. that the boat which was the subject of Pud's calcs may have had a considerable wetted area (such as a long-keeler with a bluff bow) and 2. you are totally inaccurate in the second statement, I have experienced such sheering in the Med where the rules are that winds both gust by 2-3 forces and vary by 45-60 degrees.
noelex
Well-Known Member
[ QUOTE ]
Quoting Fraysse out of context is, being kind, an unwise move, especially in view of the caveats he puts on the spreadsheet.
You have ignored two other possibilities:- 1. that the boat which was the subject of Pud's calcs may have had a considerable wetted area (such as a long-keeler with a bluff bow) and 2. you are totally inaccurate in the second statement, I have experienced such sheering in the Med where the rules are that winds both gust by 2-3 forces and vary by 45-60 degrees.
[/ QUOTE ]
Fraysse measurements certain fit in with the calculations from other bodies. He provides all the assumptions behind his calculations which look reasonable to me.
The suggestion that a seven knot current is equivalent to an 82K wind instead of 30K means the calculated ratio of forces wind to current is nearly 10X different. So someone must be wrong. Differences in the ratio between wetted surface and aerodynamic drag between vessels would not be enough to account for the discrepancy in the calculations.
A light fin keeled yacht with a partial rope rode will shear about more than other vessels which may explain why you have seen your yacht sail upwind of the anchor and I have not. It shows the wisdom of the adage of anchoring near boat of the same type on the same rode. In the conditions talked about most boats will have over 50m of rode out. If your yacht sails over 50m upwind in gusts during strong winds I will keep my distance.
Quoting Fraysse out of context is, being kind, an unwise move, especially in view of the caveats he puts on the spreadsheet.
You have ignored two other possibilities:- 1. that the boat which was the subject of Pud's calcs may have had a considerable wetted area (such as a long-keeler with a bluff bow) and 2. you are totally inaccurate in the second statement, I have experienced such sheering in the Med where the rules are that winds both gust by 2-3 forces and vary by 45-60 degrees.
[/ QUOTE ]
Fraysse measurements certain fit in with the calculations from other bodies. He provides all the assumptions behind his calculations which look reasonable to me.
The suggestion that a seven knot current is equivalent to an 82K wind instead of 30K means the calculated ratio of forces wind to current is nearly 10X different. So someone must be wrong. Differences in the ratio between wetted surface and aerodynamic drag between vessels would not be enough to account for the discrepancy in the calculations.
A light fin keeled yacht with a partial rope rode will shear about more than other vessels which may explain why you have seen your yacht sail upwind of the anchor and I have not. It shows the wisdom of the adage of anchoring near boat of the same type on the same rode. In the conditions talked about most boats will have over 50m of rode out. If your yacht sails over 50m upwind in gusts during strong winds I will keep my distance.
HoratioHB
Well-Known Member
Re: To add to pud\'s post
[ QUOTE ]
An option which I've found works extremely well (and mine is a lightweight fin keel which is appalling at sheering around and sailing up to the anchor) is to dig in @ 5:1 or more, on chain, then attach a textile rode at about 1/2 depth and leave sufficient bight of chain to touch the bottom. That cuts out all sheering and even seems to be an improvement on two anchors at an angle.
[/ QUOTE ]
Charles - are you saying you use effectively a very long snubber attached at half water depth and then let out a lot more chain so it touches the bottom behind the snubber? Interesting idea- I use a 5m long snubber already and shear about like mad but have never let out such a large bight of chain.
I assume it works due to the drag of the second bight on the bottom.
[ QUOTE ]
An option which I've found works extremely well (and mine is a lightweight fin keel which is appalling at sheering around and sailing up to the anchor) is to dig in @ 5:1 or more, on chain, then attach a textile rode at about 1/2 depth and leave sufficient bight of chain to touch the bottom. That cuts out all sheering and even seems to be an improvement on two anchors at an angle.
[/ QUOTE ]
Charles - are you saying you use effectively a very long snubber attached at half water depth and then let out a lot more chain so it touches the bottom behind the snubber? Interesting idea- I use a 5m long snubber already and shear about like mad but have never let out such a large bight of chain.
I assume it works due to the drag of the second bight on the bottom.
charles_reed
Well-Known Member
To correct our misapprehensions
I would assume the 82kt is a typo for 32kt.
I never used any rope, when the boat sheered around (perhaps you need to digest Fraysse more thoroughly to appreciate the reason).
I now use rope on chain with a large bight of chain on the other side from the anchor rode.
Whether or not you believe this has stopped any sheering about is immaterial to me as I have satisfied myself of its effectiveness.
Obviously I did not make myself clear - wind shifts through 30 degrees will frequently find you upwind of your anchor when the next gust comes round from the original direction.
Most recent recorded incident
Port Mon 43˚00.80’N 06˚24.81’E 09/07/2008 13:00 - 10:45
I was anchored fore-aft watching all the others dance into each other.
Incidentally I do hope we're talking about the same thing
if you're talking about http://en.wikipedia.org/wiki/Shear
and I'm talking about http://en.wiktionary.org/wiki/sheer being the noun or verb there's little hope of our ever agreeing
I would assume the 82kt is a typo for 32kt.
I never used any rope, when the boat sheered around (perhaps you need to digest Fraysse more thoroughly to appreciate the reason).
I now use rope on chain with a large bight of chain on the other side from the anchor rode.
Whether or not you believe this has stopped any sheering about is immaterial to me as I have satisfied myself of its effectiveness.
Obviously I did not make myself clear - wind shifts through 30 degrees will frequently find you upwind of your anchor when the next gust comes round from the original direction.
Most recent recorded incident
Port Mon 43˚00.80’N 06˚24.81’E 09/07/2008 13:00 - 10:45
I was anchored fore-aft watching all the others dance into each other.
Incidentally I do hope we're talking about the same thing
if you're talking about http://en.wikipedia.org/wiki/Shear
and I'm talking about http://en.wiktionary.org/wiki/sheer being the noun or verb there's little hope of our ever agreeing
Sandyman
Well-Known Member
Re: To correct our misapprehensions
.................................................................................................
I now use rope on chain with a large bight of chain on the other side from the anchor rode.
Whether or not you believe this has stopped any sheering about is immaterial to me as I have satisfied myself of its effectiveness.
.......................................................................................................
Blimey. I was going to ask the same question Horatio. Perhaps im glad now that i didn't. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
I think your assumptions must be correct.
.................................................................................................
I now use rope on chain with a large bight of chain on the other side from the anchor rode.
Whether or not you believe this has stopped any sheering about is immaterial to me as I have satisfied myself of its effectiveness.
.......................................................................................................
Blimey. I was going to ask the same question Horatio. Perhaps im glad now that i didn't. /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
I think your assumptions must be correct.
noelex
Well-Known Member
Re: To correct our misapprehensions
[ QUOTE ]
I would assume the 82kt is a typo for 32kt.
Obviously I did not make myself clear - wind shifts through 30 degrees will frequently find you upwind of your anchor when the next gust comes round from the original direction.
[/ QUOTE ]
I think we are getting too much into mechanics here and away from anchors, but to answer your questions.
The 82k was not a misprint by me. It refers to Puds original contention (that I disagreed with) that a 7k current produced the same force as a 82k wind.
I think I understand your concept of sheering upwind. It refers to the Yaw axis in aerodynamics.
If we assume a yacht is anchored 50m back from the anchor & the wind is gusting 60 degrees (30 degrees each side of the mean). If the gusts last long enough & the yacht stretches out the rode. It is swinging roughly 50m from side to side but will move forward into wind only 7m.
It would have to sail into wind a further 43m into the wind, dragging the anchor chain, to overtake and become windward of the anchor.
I can only comment on yachts I have owned which don't move forward like this to overtake the anchor. I have never seen a gps plot or a transit position in strong wind where my yacht was upwind of the anchor
[ QUOTE ]
I would assume the 82kt is a typo for 32kt.
Obviously I did not make myself clear - wind shifts through 30 degrees will frequently find you upwind of your anchor when the next gust comes round from the original direction.
[/ QUOTE ]
I think we are getting too much into mechanics here and away from anchors, but to answer your questions.
The 82k was not a misprint by me. It refers to Puds original contention (that I disagreed with) that a 7k current produced the same force as a 82k wind.
I think I understand your concept of sheering upwind. It refers to the Yaw axis in aerodynamics.
If we assume a yacht is anchored 50m back from the anchor & the wind is gusting 60 degrees (30 degrees each side of the mean). If the gusts last long enough & the yacht stretches out the rode. It is swinging roughly 50m from side to side but will move forward into wind only 7m.
It would have to sail into wind a further 43m into the wind, dragging the anchor chain, to overtake and become windward of the anchor.
I can only comment on yachts I have owned which don't move forward like this to overtake the anchor. I have never seen a gps plot or a transit position in strong wind where my yacht was upwind of the anchor
HoratioHB
Well-Known Member
Re: To correct our misapprehensions
Charles - if I may interupt your ongoing debate and ask again for more information about the idea of using the bight behind the snubber to stop shearing, as its new to many of us.
What kind of material is your line? - my snubber is stretchy nylon to act as a shock absorber is this what you use.
Do you know what is the key factor of this set up that stops the shear, for example is it the drag of the anchor chain across the bottom or just the drag/inertia of that extra chain through the water?
I shall try this out as soon as I am back on the boat as it seems the best idea I have heard so far and I'm sure others reading this would also want to know more.
Charles - if I may interupt your ongoing debate and ask again for more information about the idea of using the bight behind the snubber to stop shearing, as its new to many of us.
What kind of material is your line? - my snubber is stretchy nylon to act as a shock absorber is this what you use.
Do you know what is the key factor of this set up that stops the shear, for example is it the drag of the anchor chain across the bottom or just the drag/inertia of that extra chain through the water?
I shall try this out as soon as I am back on the boat as it seems the best idea I have heard so far and I'm sure others reading this would also want to know more.
jimbaerselman
Well-Known Member
Re: To correct our misapprehensions
I use a similar technique to Charles; a minimum of 20m of snubber line, which gives me about 4m of 'spring' to reduce the shocks at each end of the yaw. And a great big loop of chain hanging in the water, which reduces the yawing a bit.
There are big differences between boat types when yawing from side to side. Those with high directional stability yaw less than those with low directional stability, and those with good yaw damping (long keels) yaw less than those with light yaw damping (short keels). And bow windage, as apart from stern windage, also increases the yawing.
Forked moors kill the effect of yawing on anchor pull angles; the anchor which checks your motion lies in line with the force being applied; very useful.
I use a similar technique to Charles; a minimum of 20m of snubber line, which gives me about 4m of 'spring' to reduce the shocks at each end of the yaw. And a great big loop of chain hanging in the water, which reduces the yawing a bit.
There are big differences between boat types when yawing from side to side. Those with high directional stability yaw less than those with low directional stability, and those with good yaw damping (long keels) yaw less than those with light yaw damping (short keels). And bow windage, as apart from stern windage, also increases the yawing.
Forked moors kill the effect of yawing on anchor pull angles; the anchor which checks your motion lies in line with the force being applied; very useful.
noelex
Well-Known Member
Re: To correct our misapprehensions
Horatio
Getting back to the real topic. If you have chain left over when anchoring in strong conditions it is certainly worth dropping on the bottom it will help dampen the sheering as Charles said in addition it provides a slight kellet effect and by reducing the weight in the bow it reduces pitching. I cannot see any benefit in leaving chain in the anchor locker. (this assumes you have an electric anchor winch and be careful leaving it down in very light conditions as your boat will swing differently to your neighbors)
Unfortunately in strong wind I often have all my chain out.
A couple of other suggestions you may like to try.
It has been suggested suspending a bucket from the chain near the bow reduces sheering. I have never tried it myself, but the person that recommended it on another forum was an experienced and knowledgeable sailor.
There are also people that advocate anchoring from the stern to reduce the amount of sheering or taking an additional line from midships position to skew the vessel 20 degrees or so.
Having 2 snubbers in a bridle fashion from the bow sometimes makes a small difference.
Finally reducing windage at the front of the boat will always help in all ways or even deliberately increasing windage at the back.
If all else fails and your yacht is sheering a lot, a riding sail may be worth considering.
These options may be worth a try in moderate conditions to see if they help.
Horatio
Getting back to the real topic. If you have chain left over when anchoring in strong conditions it is certainly worth dropping on the bottom it will help dampen the sheering as Charles said in addition it provides a slight kellet effect and by reducing the weight in the bow it reduces pitching. I cannot see any benefit in leaving chain in the anchor locker. (this assumes you have an electric anchor winch and be careful leaving it down in very light conditions as your boat will swing differently to your neighbors)
Unfortunately in strong wind I often have all my chain out.
A couple of other suggestions you may like to try.
It has been suggested suspending a bucket from the chain near the bow reduces sheering. I have never tried it myself, but the person that recommended it on another forum was an experienced and knowledgeable sailor.
There are also people that advocate anchoring from the stern to reduce the amount of sheering or taking an additional line from midships position to skew the vessel 20 degrees or so.
Having 2 snubbers in a bridle fashion from the bow sometimes makes a small difference.
Finally reducing windage at the front of the boat will always help in all ways or even deliberately increasing windage at the back.
If all else fails and your yacht is sheering a lot, a riding sail may be worth considering.
These options may be worth a try in moderate conditions to see if they help.
