toyed with the idea a couple of years ago, but the details were a bit different.
Where I am, coastal areas arent that deep, so even If i sank to the bottom, it wouldn't be that difficult to rescue me, specially since coastal towns always have fishermen around the area who might see me jump.
Another thing I'd have to factor in was tides. High/low tides usually last only 4 or 5 hours depending on the area, so the depth would really be a problem specially since I personally didnt want to be found.
another factor would be currents. It's quite possible that I might not be able to calculate the weight I needed to stay at the bottom correctly and end up just being washed to shore because of how strong the current can be.
even if i'd choose a cliffside location, i'd need to go down the side of the cliff to find out how deep it goes first.
haven't even gotten to the SI part yet. I'd need to be completely out of it so I dont struggle and accidently swim back to shore with the weight on.