Amount of Scope for Anchoring
Where:
d: Water depth(m)
L: Minimum Required Length of Anchor Chain(m)
・Japanese Publication Theory of Ship Operation
Fine weather: L=3d+90m
Rough weather: L=4d+145m
・United Kingdom Publication Theory of Ship Operation
L=39 ×√ d
Lots of interesting info about dragging anchor, use of two anchors etc
Preventing an Anchor from Dragging
Lots more info if you follow the link at the bottom to the pdf file
It’s surprising how little extra holding power you get from running out extra shots.
From this site
[QUOTE=Kennebec Captain;131923]It’s surprising how little extra holding power you get from running out extra shots.[/QUOTE]
I think that is not entirely accurate. While the chain itself does not actually hold much of anything, the whole idea behind added shots of chain is to weigh down the rode to where it cannot lift which if it does causes the anchor shank to rise compromising the anchor from holding. Of course, the type and size of anchor used in relation to the type of bottom is also a critical consideration in this equation.
[QUOTE=c.captain;131927]I think that is not entirely accurate. While the chain itself does not actually hold much of anything, the whole idea behind added shots of chain is to weigh down the rode to where it cannot lift which if it does causes the anchor shank to rise compromising the anchor from holding. Of course, the type and size of anchor used in relation to the type of bottom is also a critical consideration in this equation.[/QUOTE]
The calculations are for anchor and chain together. On the pdf file they do the calculation running out to 12 shots of chain. If I am reading it correctly they are saying you will drag with 5 more kts of wind. (1 m/s is about 2 kts)
[QUOTE=Kennebec Captain;131930]The calculations are for anchor and chain together. On the pdf file they do the calculation running out to 12 shots of chain. If I am reading it correctly they are saying you will drag with 5 more kts of wind. (1 m/s is about 2 kts)[/QUOTE]
Like I said, I do not believe that is entirely accurate. Been anchored up at St. Paul Island, Alaska with a 200’ processing ship with a 8000# anchor and 6 shots of 2.5" chain and started to drag in 60kts sustained so slipped two more shots and he held fast albeit yawed all over Kingdom Come and back. Amazing how a aft house vessel can flail in the wind like that.
Never did much try two anchors to increase holding but wondering if anyone has anchored in a strong tidal stream with a “Bahamian” moor? Did that once and it was amazing how well it worked. Each change of the tide, the vessel would change the direction it pointed but swung nothing more than its own length. Simply beautiful, but there always needs to be a bit of tension on both cables to prevent the vessel from turning 360!
[QUOTE=c.captain;131937]Like I said, I do not believe that is entirely accurate. Been anchored up at St. Paul Island, Alaska with a 200’ processing ship with a 8000# anchor and 6 shots of 2.5" chain and started to drag in 60kts sustained so slipped two more shots and he held fast albeit yawed all over Kingdom Come and back. Amazing how a aft house vessel can flail in the wind like that.
Never did much try two anchors to increase holding but wondering if anyone has anchored in a strong tidal stream with a “Bahamian” moor? Did that once and it was amazing how well it worked. Each change of the tide, the vessel would change the direction it pointed but swung nothing more than its own length. Simply beautiful, but there always needs to be a bit of tension on both cables to prevent the vessel from turning 360![/QUOTE]
That’s very heavy gear in relationship to the size of the vessel.
I was anchored up on the other side of St Paul the night the All Alaskan went around with either 4 or 5 shots out.
[QUOTE=Kennebec Captain;131941]That’s very heavy gear in relationship to the size of the vessel.
I was anchored up on the other side of St Paul the night the All Alaskan went around with either 4 or 5 shots out.[/QUOTE]
The GALAXY had some awesome heavy anchor tackle. If you every see photos of her note how large the anchors appear in relation to the hull size? I think they were old Liberty Ships anchors in memory serves me.
[QUOTE=Kennebec Captain;131941]That’s very heavy gear in relationship to the size of the vessel.
That’s what I was thinking too - very heavy gear
On the other hand, that’s the kind of gear that one needs in Alaska.
I mostly lay on the tow wire. I find that an extra shot of surge gear makes a world of difference.
[QUOTE=tugsailor;131960][QUOTE=Kennebec Captain;131941]
That’s what I was thinking too - very heavy gear
On the other hand, that’s the kind of gear that one needs in Alaska.
I mostly lay on the tow wire. I find that an extra shot of surge gear makes a world of difference.[/QUOTE]
I think the calculation will differ for a vessel with low sail area and relatively heavy anchor gear compared to a vessel with large sail area and relatively light anchor gear. In the latter case the force from the wind increase more then the increase in holding power from more chain.
Actually after thinking about it after that earlier post , I recall that was the ground tackle from the OMNISEA which I never ran in the winter. The GALAXY’s ground tackle was 5000# Navy pattern stockless anchors with 1.5" chain. Always laid out at least 5 shots of scope but often 7 and sometimes even all of 9 was needed in the winter.
MY GOD! How I don’t miss Bering Sea Opilio crab season!
This formula comes very close to our SOP on o ~50,000 DWT tanker. I allow a bit more chain when expecting heavy weather but, the fair condition conclusion seems right on for my ship. I am assuming decent holding ground. We work very hard in heavy winds when light. The bow gets trucking and pops the anchor. Extra chain early prevents ass ache. I’ve had little success stopping dragging by slipping more chain. We usually need to pick up and reset once she gets moving. We usually schedule this maneuver for 0200 when it’s raining sideways at 35 degrees. We attempt the maneuver at least three times to be sure we’ve gotten it right. We then pick it up and slow steam until the weather passes. Greater than force six… We’re going for a cruise. Screw the office.
[QUOTE=Radiocheck;131969]This formula comes very close to our SOP on o ~50,000 DWT tanker. I allow a bit more chain when expecting heavy weather but, the fair condition conclusion seems right on for my ship. I am assuming decent holding ground. We work very hard in heavy winds when light. The bow gets trucking and pops the anchor. Extra chain early prevents ass ache. I’ve had little success stopping dragging by slipping more chain. We usually need to pick up and reset once she gets moving. We usually schedule this maneuver for 0200 when it’s raining sideways at 35 degrees. We attempt the maneuver at least three times to be sure we’ve gotten it right. We then pick it up and slow steam until the weather passes. Greater than force six… We’re going for a cruise. Screw the office.[/QUOTE]
We jack around pretty hard sometime, it starts at a little over 20 kts and increases as the wind increases. . The paper calls it horsing. At 35 kts it gets bad and we have to watch the position closely. F-7 is maybe and she’s not going to stay put in F-8.
Current is a factor as well, She sometime really charges around with a current and wind, running up towards the anchor then putting the wind almost abeam and going for a run like a dog on a chain chasing a cat. I guesstimate that 1 kt of current is equivalent to 10 kts of wind.
I’ve had the same experience as you with dragging, once they start going it’s all over, the big ones anyway. .The linked paper has some good info on how much sea room is needed to recover the anchor and how much speed and room is required to regain control. Takes a lot of acreage.
I can’t low speed steam until we make some technical changes , that’s a big problem. Sometimes I drift which sucks but sometime I’ve got no choice but to run.
I did get in a pickle one time and couldn’t leave, I called a couple of tugs and they held the bow into the wind and she stayed put ifn 50+ kts but it was exhausting work. Lucky it was only a few hours. The paper talks about using the bow thruster, I can cut down on the jacking a little with judicious use of the thruster but you don’t gain that much,
I have seen other assessments and guidelines on vessel operations from Japanese sources. I wouldn’t trust any of it not for a second.
[QUOTE=highseasharry;132055]I have seen other assessments and guidelines on vessel operations from Japanese sources. I wouldn’t trust any of it not for a second.[/QUOTE]
Which part do you disagree with? The use of the Hughes formula for calculation of the wind loads? The formula for cantenary? The anchor / chain holding power calculations? The ship speeds required to turn into the wind? The time /distance to recover the anchor and control the ship?
It contains all the usual “your mileage may vary” caveats, what do you find wrong with it aside from the fact that the source is Japanese?
Edit: This search: “hughes formula” anchor dragging - results in a all English version which is much more readable.
I routinely use 2 anchors in any river with a reversing current. It works quite well as long as the scopes and chain are set up so that they don’t come taught under the boat and foul your running gear.
The worst place that I have anchored had a strong reversing current and wind funneling down the river that sometimes worked out just “right”, or maybe just “wrong”, so that wind force and current force were almost the same but in opposite directions and the boat was kind of orbiting all over the place. I have also noticed all the freighters anchored off the island I live on do not ride the same. The loaded ones change direction with the tide and the light ones change with the wind.
[QUOTE=c.captain;131937]Like I said, I do not believe that is entirely accurate. Been anchored up at St. Paul Island, Alaska with a 200’ processing ship with a 8000# anchor and 6 shots of 2.5" chain and started to drag in 60kts sustained so slipped two more shots and he held fast albeit yawed all over Kingdom Come and back. Amazing how a aft house vessel can flail in the wind like that.
Never did much try two anchors to increase holding but wondering if anyone has anchored in a strong tidal stream with a “Bahamian” moor? Did that once and it was amazing how well it worked. Each change of the tide, the vessel would change the direction it pointed but swung nothing more than its own length. Simply beautiful, but there always needs to be a bit of tension on both cables to prevent the vessel from turning 360![/QUOTE]
[QUOTE=c.captain;131968]Actually after thinking about it after that earlier post , I recall that was the ground tackle from the OMNISEA which I never ran in the winter. The GALAXY’s ground tackle was 5000# Navy pattern stockless anchors with 1.5" chain. Always laid out at least 5 shots of scope but often 7 and sometimes even all of 9 was needed in the winter.
MY GOD! How I don’t miss Bering Sea Opilio crab season![/QUOTE]
I was on the COASTAL STAR back in the day (remember the sail area on that house?). We NEVER put out both anchors, and most of the time we had a tramper equal length as us on one side (300’?) and a crab boat on the other.
Riding out enormous swells and 60-70 knot winds (the wind guage blew off the first week!)
Sure we woud go hide on the lee-side of St. Matthew or St. Paul Island when we had the chance, but we didnt always have a chance.
Just saying we paid out ALL the chain (9 shots?) except for the bitter end, It held most of the time. (I forget the size of the anchors, but they were quite huge, 2.5" chain I believe)
Saw one tramper try two anchors, the chains got twisted, the cargo shifted, and there they were heeled over up to the handrails on one side.
Imagine having BOTH of your chains/anchors fouled in an arctic storm, too rough to step foot on deck, heeled over a good 25+ degrees.
MY GOD! How I don’t miss Bering Sea King/Baridi/Opilio crab season!
AMEN BROTHER!
[QUOTE=stellarseas;133032]I was on the COASTAL STAR back in the day (remember the sail area on that house?). We NEVER put out both anchors, and most of the time we had a tramper equal length as us on one side (300’?) and a crab boat on the other.
Riding out enormous swells and 60-70 knot winds (the wind guage blew off the first week!)
Sure we woud go hide on the lee-side of St. Matthew or St. Paul Island when we had the chance, but we didnt always have a chance.
Just saying we paid out ALL the chain (9 shots?) except for the bitter end, It held most of the time. (I forget the size of the anchors, but they were quite huge, 2.5" chain I believe)
Saw one tramper try two anchors, the chains got twisted, the cargo shifted, and there they were heeled over up to the handrails on one side.
Imagine having BOTH of your chains/anchors fouled in an arctic storm, too rough to step foot on deck, heeled over a good 25+ degrees.
…[/QUOTE]
I tried dropping a second anchor underfoot a couple of times (600+ ft ship) to try an dampen the “horsing” around in the wind but it didn’t seem to help any that I could see. The publication in the 1st post says two anchors is not worth the risk, for large ships even if they are not in danger of fouling together because if you have to move you have a big problem on your hands trying to recover two anchors in adverse weather. I agree.
A fair number of boats with all-chain rodes will have some nylon line between the last link of the chain and the boat. That way if you have to make a quick escape you can let the windlass run free and cut the nylon. If the chain is attached to the boat down in the chain locker it is not easy to get loose quickly. Do ships do something similar or are you just hosed if you need to drop and run?
[QUOTE=stellarseas;133032]I was on the COASTAL STAR back in the day (remember the sail area on that house?). We NEVER put out both anchors, and most of the time we had a tramper equal length as us on one side (300’?) and a crab boat on the other.
Riding out enormous swells and 60-70 knot winds (the wind guage blew off the first week!)
Sure we woud go hide on the lee-side of St. Matthew or St. Paul Island when we had the chance, but we didnt always have a chance.
Just saying we paid out ALL the chain (9 shots?) except for the bitter end, It held most of the time. (I forget the size of the anchors, but they were quite huge, 2.5" chain I believe)
[B]Saw one tramper try two anchors, the chains got twisted, the cargo shifted, and there they were heeled over up to the handrails on one side.
Imagine having BOTH of your chains/anchors fouled in an arctic storm, too rough to step foot on deck, heeled over a good 25+ degrees.
[/B]
MY GOD! How I don’t miss Bering Sea King/Baridi/Opilio crab season!
AMEN BROTHER![/QUOTE]
[QUOTE=stellarseas;133032]I was on the COASTAL STAR back in the day (remember the sail area on that house?). We NEVER put out both anchors, and most of the time we had a tramper equal length as us on one side (300’?) and a crab boat on the other.
Riding out enormous swells and 60-70 knot winds (the wind guage blew off the first week!)
Sure we woud go hide on the lee-side of St. Matthew or St. Paul Island when we had the chance, but we didnt always have a chance.
Just saying we paid out ALL the chain (9 shots?) except for the bitter end, It held most of the time. (I forget the size of the anchors, but they were quite huge, 2.5" chain I believe)
Saw one tramper try two anchors, the chains got twisted, the cargo shifted, and there they were heeled over up to the handrails on one side.
Imagine having BOTH of your chains/anchors fouled in an arctic storm, too rough to step foot on deck, heeled over a good 25+ degrees.
MY GOD! How I don’t miss Bering Sea King/Baridi/Opilio crab season!
AMEN BROTHER![/QUOTE]
Yeah, isn’t it something sobering to think back to the bad old daze and the shit we dealt with on a daily basis. As I have said many times here before that it is adversity that makes the man a truly capable mariner and these button pushing pukes of today coming out of school would be utterly useless working on a real vessel. Too much automation and political BS is turning these kids into prima dona ballerinas only working at sea for the “easy” money!
effing little shitz!
[QUOTE=yacht_sailor;133091]A fair number of boats with all-chain rodes will have some nylon line between the last link of the chain and the boat. That way if you have to make a quick escape you can let the windlass run free and cut the nylon. If the chain is attached to the boat down in the chain locker it is not easy to get loose quickly. Do ships do something similar or are you just hosed if you need to drop and run?[/QUOTE]
At least some ships are equipped with some kind of arrangement where the pin or whatever can be pulled on the last shot without too much difficulty. Hopefully there enough tricks up the sleeve it doesn’t come to that. The key factor is how much room you have to leeward. If it’s tight it’s prudent to pick up and leave before you are forced to.
[QUOTE=c.captain;133093]Yeah, isn’t it something sobering to think back to the bad old daze and the shit we dealt with on a daily basis. As I have said many times here before that it is adversity that makes the man a truly capable mariner and these button pushing pukes of today coming out of school would be utterly useless working on a real vessel. Too much automation and political BS is turning these kids into prima dona ballerinas only working at sea for the “easy” money!
effing little shitz![/QUOTE]
Did you mean a “prima ballerina”? Because a “prima donna” is is a singer in an opera. How can you be “prima donna ballerina”?
