Rhylsailer99
Active member
My mooring ring is buried and I was thinking to attach a big buoy low down to lift the chain. Would this lift the mooring ring and expose the ground chains as I really do not want to dig them out.
Depends on a few factors:-My mooring ring is buried and I was thinking to attach a big buoy low down to lift the chain. Would this lift the mooring ring and expose the ground chains as I really do not want to dig them out.
We are not clairvoyant.
Did your boat start to do a headstand? A fine party trick!If it's tidal and you own a boat wait until low water, rig a strong rope from the ring to your boat, remove the slack but make sure you can pay it off if your boat doesn't start to lift when the tide rises.
I did this on my mooring with a Leisure 23, trying to lift the ground chain (not a riser), it didn't work but it provided entertainment to boats leaving the near by dock![]()
Posters seem to assume that moorings etc should be lifted from the bow. What is far better is to lift from the middle of the boat by a bridle under the hull. On a yacht often the sheet winches are in just the right place or on a mobo a rope right around the hull over the open area. Of course with a fin keel boat you lose a lot of lifting space. Here the situation does not arise so much with minimum tides SCUBA diving tot he mooring and replace chain as necessary. Chains are not dropped for winter.
ol'will
"To lift a mass of 1kg underwater the airbag needs to displace 1kg of water."I was thinking to attach a big buoy low down to lift the chain
All very well, but a properly designed mooring sinker may well have a concave surface underneath to provide greater suction. By no means all do, but those that do can require a great deal more lift to break the suction, possibly in order of tons more than the actual weight of the gear.
There is your first mistake. If the sinker was made of styrofoam & 3 M tall Your pressure difference would be based on 3 MetresA very good point. Let's do some back-of-fag-packet calculations:
The max suction force is the max pressure difference possible between the top and bottom of the sinker x the area of the sinker.
There is your first mistake. If the sinker was made of styrofoam & 3 M tall Your pressure difference would be based on 3 Metres
If it was lead & 300mm tall your pressure difference between top & bottom of the sinker would be minimal
But the weight of the second sinker would be significantly greater & more likely to have greater holding power
Where do your figures allow for that?
If you read the post i was demonstrating that the height of the sinker was irrelevant. It could be very tall or very shallow. as in one made of polystyrene or lead. But the combined weights are actually what forces the sinker downwards. you are not making allowances for these pointsKeep up at the back! The calculation was for the effect of suction - I made no attempt to calculate the total holding power, which of course does depend on the weight.
But the pressure difference is between atmospheric pressure, about 105 Pascals, and a vacuum. the water depth adds a surprisingly small amount unless the water is deep; it only doubles the suction force at 10m.