weights advice please

[Outbound]

It is the "bestest" because it is real world with real gear on a real dive and not just a numbers/math game.

But it's always a numbers and math game. We know what a cubic foot of air weighs. We know how many cubic feet of air are in a full AL80.

I agree that for people who already have their weight more or less dialed in but might want to tweak it a bit, the 500psi weight check is a good way to go. You finish a dive and think that maybe you are a tab heavy and can drop some weight. You come up with say 800 psi, so you purge down to 500 and do a weight check then at the end of a dive. But if you are just starting out and have no idea how much weight to use that's not really practical. Are you going to ask the dive shop to give you a 500 psi tank - or purge down a full tank - so you can do a weight check? Then you dial in your weight and have to get back out to swap to a full tank so you can actually start your dive.

 

[Doby45]

But it's always a numbers and math game. We know what a cubic foot of air weighs. We know how many cubic feet of air are in a full AL80.

I agree that for people who already have their weight more or less dialed in but might want to tweak it a bit, the 500psi weight check is a good way to go. You finish a dive and think that maybe you are a tab heavy and can drop some weight. You come up with say 800 psi, so you purge down to 500 and do a weight check then at the end of a dive. But if you are just starting out and have no idea how much weight to use that's not really practical. Are you going to ask the dive shop to give you a 500 psi tank - or purge down a full tank - so you can do a weight check? Then you dial in your weight and have to get back out to swap to a full tank so you can actually start your dive.

okie dokie

 

[Bob DBF]

All divers are overweighted at the beginning of their dive so that they are properly weighted at the end of their dive.

How do you know you are properly weighted at the end of the dive without actually checking, overweighted is a large area to start from. With no other information to work from, it's a place to start, but why not do an accurate check when you can.

15' with 300-500# in the tank and an empty BC insures the minimum weight needed for the dive. Once known it is easier and more accurate to figure the difference between tanks or rigs. This is not to say one can not dive with more weight, however one would know how much they are overweighted.


Bob

 

[broncobowsher]

20+ years of diving later I still do this.

At the end of a dive (where stuff may be different then normal) do another weight check. Dump air and see how you sink. If you drop like a rock, pull a little weight and try again. Don't worry about trim, just weight. Once you get to the barely sink stage, get out of the water. Now re-configure the weights into a balanced load. This is the final polish, not the rough cut you start at.

Yes, the first dive tends to put me a bit over-weight. But nothing insane. better then too light at the end. I have made that mistake before and had to carry a rock at the end of the dive to make up for it.

 

[Outbound]

How do you know you are properly weighted at the end of the dive without actually checking, overweighted is a large area to start from. With no other information to work from, it's a place to start, but why not do an accurate check when you can.

Sorry, I should have clarified. What I meant is that everyone diving an AL80, even once properly weighted, will have an extra 5-6 lbs of weight on them at the start of a dive because that is the weight of the air in their tank. For example, in tropical salt water with a 3mm full wetsuit and my current gear, I will float at around eye level with no extra lead with a full tank. If I exhale I will sink. But I know my tank is going to get 5-6 lbs lighter over the course of a dive, so I add that weight to my belt. I'm now overweighted for the start of my dive, but will be at the correct weight to hold a safety stop at the end of my dive.

As we all know, being properly weighted means having the exact weight necessary to hold a safety stop with 500 psi in the tank. But, knowing the weight of air, you need not have 500 psi in your tank in order to do a weight check. You can do it with any amount of air so long as you take that weight into consideration. I just think that, if you are just starting out and have no idea how much weight you'll need, it's more practical to start with a full tank and calculate from there than it is to try to get your hands on a 500 psi tank. It's a different story if you already have a good idea of your weighting needs but think you need to tweak it a bit for your next dive. In that case, you can do a weight check at the end of a dive with an "empty" tank.

 

[mi000ke]

I put together a spreadsheet for myself that computes my net buoyancy (with and without weights) based on the buoyancy of my body, BCD, wetsuit, fins, tank, regs, and any other crap I'm taking along on my dive (pony, camera, etc.)

It computes net buoyancy at three time points (beginning, middle, end) and 5 depths based on atmospheres (0, 16.5, 33, 66, 99). This accounts for the changing compression of the wet suit at different depths, plus the use of air.

I have two weighting goals: 1) to use the minimum amount of weight that enables me to descend at the beginning of my dive (w/tank full), and 2) to use the correct weight that keeps me neutral at my safety stop (assume at 16.5' to make the math easier) with 500 psi in my tank at the end of my dive.

So for me, I am typically 10# buoyant on the surface at start of dive (I use the same rig pretty much every time), so I use 12 # to get me down (could use 11 I suppose but hard to divide into even weights). And by the end of the dive at at 16.5' safety stop I am 11# buoyant (so with 12# of weight, technically I am -1 at 16.5', but at 15' I should be pretty close to neutral, and in actuality in the water I am able to hold neutral with no air in my BCD anywhere between 10-20'). I tried 10# but had to work too hard (duck dive) to get down, and was a little floaty at safety stop. So the spreadsheet seems to work pretty well.

I am about to change to a lighter wetsuit (5mm to 3mm), and just plugged in the new numbers. Planning to try the predicted weight (8#) on my next dive.

 

[yle]

But it's always a numbers and math game. We know what a cubic foot of air weighs. We know how many cubic feet of air are in a full AL80.

Some people completely trust numbers & math, some people don't. Do it whichever way you're comfortable with, as long as you understand the method you're using.

I'm totally with the math side of things, but I know not everyone is like me.