Mike Veitch:
No offense meant but this thread just goes to show what i see everyday with part time divers. Everyone loves too much weight...
As i said, no offense, just a huge pet peeve!
I'm going to sidestep the "overweighting" debate, although I will say that what we really need to remember is that bouyancy control is not weighting, and weighting is not bouyancy control, even though good weighting makes bouyancy control easier.
If we want to critcize "part timers", perhaps we should remember to account for that on average, their wetsuits probably haven't had as many dives on them to crush up their wetsuit and thus, decrease its overall buoyancy.
Since few people buy old, worn out wetsuits, its IMO a futile exercise to suggest how much weight to wear with a "dead" (or even "half dead") wetsuit....I've had full 3mm suits that initially took ~5lbs to sink that after a few seasons were sent to the bottom of the pool with but a single 1lb weight...that's only an ~80% change in bouyancy
And FWIW, BC's can vary very widely too...I've seen BC's (without_ metal backplates!) that were anywhere from -1lbs to +6lbs when completely empty.
FWIW, the easiest way to measure how much weight it takes to sink a wetsuit (or whatever!) is to throw it in a mesh bag with some weights, then toss the bag into a swimming pool. If it floats, increase the weights until it sinks. If it sinks, take weights out. To go a bit further, you can lighten up the bag and drag it underwater to also experimentally determine its net bouyancy at some depth (such as 10ft or 15ft).
FWIW, my personal rule of thumb is that my weightbelt will weigh <10lbs with any warmwater setup and <30lbs with any variation on a 7mm farmer john setup.
Do I ever dive with 10lbs/30lbs? Sure, for a dive or two, as this is only intended to be a parametric "upper limit" to use as starting points for when an old wetsuit gets replaced with a new one, and I need to choose something as a new starting point.
I'll sort out by how much I'm overweighted on that dive and then proceed to reduce ballast over time...since a wetsuit always loses bouyancy, weighting needs always go down...regardless of diver "skill" (or ego
.
BTW,
7mm suit, was 6lbs but just noticed i lost one from my pocket last week when i left it open and have done 10 or 12 dives since, sooo 4lbs. AL80 single tank, jacket BC
The laws of physics say that 4lbs will just barely sink an empty AL80, so there's something more going on here.
For example, this could be using a "dead" wetsuit, or there could be "hidden ballast" that's not being counted. Heavy jetfins and SS backplates are a common examples of the latter, but there's also body fat content as well...if the diver's BMI is well below 20%, the diver himself is a source of negative bouyancy.
Plus, there's also the question of "netural where?": stuff like wetsuits are going to be most bouyant at the surface, but many of us typically shave a few pounds off the weightbelt by instead setting up to be neutral at 15fsw when we return with an empty tank: a FJ that's +20lbs at the surface is only +14lbs at 15fsw...so there's an "easy" way to take 6lbs off the weightbelt, and we can argue that its not needed because we'll have that extra mass as a full air tank at the beginning of our dive in order to get off the surface at the beginning of the dive.
FWIW, I'm not condemning this practice (I do it myself): I'm just pointing out that it is present, and can be one of the reasons why people can come up with different values even when diving literally identical gear.
Overall, I don't know how many wetsuits one has to go through before one realizes that how much lead on your weightbelt is NOT due to "skill" that's making the biggest differences: IMO, the biggest differences are in your gear setup decisions (neutral at surface vs. neutral at 15fsw), "hidden ballast" gear choices, and how "dead" your wetsuit happens to currently be.
-hh
