That's a good way to get bent or killed.
The last thing you want is an uncontrolled pop to the surface right into a boat prop, or an unplanned ascent when you had a deco obligation.
You need enough weight to allow becoming neutral at any point below the surface, with the least amount of gas you would ever have in your tank.
The buoyancy check taught in most OW classes involves finding what it takes to just sink you with an empty (as empty as you ever expect it to be) tank and a normal breath of air. There is no calculation that will get you the correct weight. The only way to find it is to do the test.
A pound or two over won't cause much trouble, but a few pounds too light will give you an impossible-to-control safety stop and final ascent. The last 15' is the most important part of your ascent and slower is better.
Terry
I agree with much of what Terry has said, but differ on the concept of "correct weight" since some people try to tweak it too closely.
IMO, not only is it better to have an extra pound or two than be
underweighted, as Terry pointed out, it's also better than having
"correct weight" in some circumstances.
Some people try to achieve what they think is "perfect" or "correct" weighting, practically to the ounce, but they don't seem to consider that during much of the dive they are
still dealing with the
imperfect situation of having the extra weight of tank air (beginning with 6.4 lbs of air in a full al80).
Their "correct" or "perfect" weighting really only gives them only a slight advantage during most of the dive compared to someone who has a couple extra pounds. The slightly easier buoyancy control and less wasted air is a minuscule advantage really.
What about the
disadvantages? Having "correct" or "perfect" weighting has disadvantages at the end of the dive in circumstances where being able to get
negative is desirable, such as in surge or with boat props spinning above, as in Terry's scenario.
In that last scenario, positive buoyancy is clearly a problem, but so would being neutral with "correct weight" because in both cases one would have to
propel oneself away from the surface rather than just fully vent the bcd and drop down.
A prop spinning a few feet from one's head gives a new appreciation for what really constitutes "correct" weighting! Some overweighting begins to look pretty good right about then!
Dave C