I need to anchor my dock.I am going to make two cement blocks and use chain.I am going figure a scope of 5 or so.My question is,usually you drop anchor and pay out enough line to achieve correct scope,the boat drifting untill she snubs up.But I want my dock in a specific place,and will be moving the block instead.My question is,how do you figure scope and placement "in reverse"? Any thoughts would be helpfull. LLOYD
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Geof Tillotson
Is this a lake or the ocean?
If it's a lake, the issues are very different. If it's the ocean, you will need one heck of a huge cement block to overcome the lifting power of the boat and the dock due to swells, tides and wakes, let alone the salinity of the water makes everything more bouyant. Geof
If it's a lake, the issues are very different. If it's the ocean, you will need one heck of a huge cement block to overcome the lifting power of the boat and the dock due to swells, tides and wakes, let alone the salinity of the water makes everything more bouyant. Geof
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lloyd
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Geof
How large a dock?
When I was a kid, we had a dock on a small lake at a vacation home that was kept in place with cinder blocks and chains. It was okay. Will the dock be anchored any other way? If it's a floating dock, it will probably drag cinder blocks around in any kind of wind. When I went to camp, we used very large blocks of cement in the pond to anchor the floating dock. We filled a washbasin sized container with cement for each corner of the dock. There was an eye-bolt in the middle of the cement that the chain ran down to. All in all, if the dock is free floating and has any kind of windage, I'm not sure that something that can be dragged around would be satisfactory if the winds kicked up. How do the other folks on the lake secure their docks? Geof
When I was a kid, we had a dock on a small lake at a vacation home that was kept in place with cinder blocks and chains. It was okay. Will the dock be anchored any other way? If it's a floating dock, it will probably drag cinder blocks around in any kind of wind. When I went to camp, we used very large blocks of cement in the pond to anchor the floating dock. We filled a washbasin sized container with cement for each corner of the dock. There was an eye-bolt in the middle of the cement that the chain ran down to. All in all, if the dock is free floating and has any kind of windage, I'm not sure that something that can be dragged around would be satisfactory if the winds kicked up. How do the other folks on the lake secure their docks? Geof
Chain length for 5 to 1 scope
First, decide where the dock is going to be located. Then check the water depth at that location. If the anchor chain is going to be attached to the deck of the dock, add the height of the deck above water to get the effective depth. Multiply by 5 (or whatever scope you finally decide on) to get the (horizontal) distance. Assuming the water isn't that deep, set a stake in the lake (a piece of 1-inch PVC pipe should be OK). Tie the end of a light line that's a little longer than the required horizontal distance to the PVC pipe. Make sure it won't slip down. Row away from the stake until you're at the end of the line. Mark the spot. The length of chain you'll need is 5.1 (square root of 26) times the effective depth. Your scope will be a little more than 5 to 1, but you're probably better off with more scope than less. If you want exactly 5 to 1, the horizontal distance would be 4.9 (square root of 24) times the effective depth. One last comment. Since you're setting chain and scope, why not use regular anchors that hook into the bottom instead of concrete blocks. They certainly would be easier to set than a huge block of concrete. In addition, the concrete loses about 40% of its weight due to buoyancy once submerged. The resistance to movement of a concrete block depends on its submerged weight. A regular anchor should offer significantly more resistance to pull. Good luck. Peter H23 "Raven"
First, decide where the dock is going to be located. Then check the water depth at that location. If the anchor chain is going to be attached to the deck of the dock, add the height of the deck above water to get the effective depth. Multiply by 5 (or whatever scope you finally decide on) to get the (horizontal) distance. Assuming the water isn't that deep, set a stake in the lake (a piece of 1-inch PVC pipe should be OK). Tie the end of a light line that's a little longer than the required horizontal distance to the PVC pipe. Make sure it won't slip down. Row away from the stake until you're at the end of the line. Mark the spot. The length of chain you'll need is 5.1 (square root of 26) times the effective depth. Your scope will be a little more than 5 to 1, but you're probably better off with more scope than less. If you want exactly 5 to 1, the horizontal distance would be 4.9 (square root of 24) times the effective depth. One last comment. Since you're setting chain and scope, why not use regular anchors that hook into the bottom instead of concrete blocks. They certainly would be easier to set than a huge block of concrete. In addition, the concrete loses about 40% of its weight due to buoyancy once submerged. The resistance to movement of a concrete block depends on its submerged weight. A regular anchor should offer significantly more resistance to pull. Good luck. Peter H23 "Raven"
Chain length for 5 to 1 scope - Part 2
The procedure is a little different if you find that the water depth at the anchor location is different from water depth at the dock. For exactly 5:1 scope: Chain length = 4.9 x (water depth at anchor location + height of cleat above water) This means the anchor has to be set farther away from the dock than originally estimated. Hopefully you're not in a situation where the bottom keeps dropping off as you move farther away.... Peter H23 "Raven"
The procedure is a little different if you find that the water depth at the anchor location is different from water depth at the dock. For exactly 5:1 scope: Chain length = 4.9 x (water depth at anchor location + height of cleat above water) This means the anchor has to be set farther away from the dock than originally estimated. Hopefully you're not in a situation where the bottom keeps dropping off as you move farther away.... Peter H23 "Raven"
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Herb Schiessl
chain location
Depending on the width of your dock, you may want to consider the left anchor attached to the right side of the dock and the oposite for the other side, so that the anchor lines form an "X" under the dock. This helps to get the chains out of the way of swimmwers, divers, boat keels, propellers etc.
Depending on the width of your dock, you may want to consider the left anchor attached to the right side of the dock and the oposite for the other side, so that the anchor lines form an "X" under the dock. This helps to get the chains out of the way of swimmwers, divers, boat keels, propellers etc.
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joe phibbs
try something other than concrete
I don't think concrete is not a suitable material to hold anything under water. Find an old engine block or transmission or something that will hold its weight down. Spend your money on a jacketed chain thru the block and shackle it to your rode. Joe
I don't think concrete is not a suitable material to hold anything under water. Find an old engine block or transmission or something that will hold its weight down. Spend your money on a jacketed chain thru the block and shackle it to your rode. Joe
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Bob
More Concrete
How long is the dock and how deep is the water? What kind of bottom do you have? (Fat is not an acceptable answer, this is not Spinal Tap!)
How long is the dock and how deep is the water? What kind of bottom do you have? (Fat is not an acceptable answer, this is not Spinal Tap!)
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