Quote:
Originally Posted by fatlazyless
... and a concrete block, 8"x8"x8" weighing about 15-lbs...and has a single large opening for attaching an anchor line
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That volume of concrete (8" cube) would be about 0.3 cu.ft and weigh around 43 lb. That "single large opening would have to be huge for the block to weigh just 15 lb, little more than a third than without the hole. Of course, a 0.3 cu.ft block weighing 43 lb out of water has a net weight of about 24 lb when submerged.