Originally Posted by Hydra
In my area, the authority in charge of moorings recommends that the weight in air of the concrete block be at least one third of the boat displacement
, because the apparent weight in water is much less...
A dead weight anchor
(mooring block) may gain some small advantage from suction in a mud bottom, otherwise it’s holding power is completely dependent
on its weight, or more exactly on it’s submerged weight
, which in the case of a concrete anchor
is almost half* its dry weight.
* The Material Displacement Factor for Concrete is 0.55
Concrete Dry Weight Required = Submerged Weight Required ÷ 0.55
If an apparent submerged weight of 1000Lbs is required:
Then 1818# dry weight is required
(1818 D.W. = 1000# S.W. ÷ 0.55)
Since concrete typically weighs about* 150 Lbs/Cubic Foot, the 1818 Lb (dry) block would be (1818 ÷ 150) about 12.12 cubic ft (or about
: 3.0' x 3.0' x 1.5')
* Concrete weight depends primarily on the density of the aggregate used. (Could vary between 75 Lb/CuFt to 160 Lb/CuFt)