Making weighting cheat sheet - assistance please.

[ScubaJill]

To help me not make weighting decisions on the fly when I'm adding in new gear like a thicker wetsuit or a steel tank when I usually dive AL80s, I'm going to create a cheat sheet that I can laminate or put into a ziplock bag with the different variables I need to take into consideration when assessing how much weight I need to add on.

Would the following formula work? +/- positive or negative buoyancy:
total positive/negative buoyancy=[(+bc) + (-regulator) + (+exposure suit) + (+hood) + (+lava core) + (+/- fins) + (+neoprene boots) + (-torch) + (+/- tank and valves @500-1000 PSI) + (+ salt water) + (+/- other equipment like camera rig)]

Experience tells me that I need to take other things into consideration for weight:
*the average depth of the dive - I get floaty above 20 feet or so. Deeper than X feet (60-80 feet?), I lose that buoyancy
*I usually have to frog kick down from the surface when wearing a wetsuit, this is pronounced on the first dive of the day
*I don't like to add air in the BC
*Practical baseline: bathing suit, bc, AL 80 at 1000 psi, regulator, torch, and floaty fins: add 6-8 pounds: so, 0+4+4-2-1+1=+6; +6-6=0; +6-8=-2.

Any help out there?

 

[Edward3c]

ScubaJill,

Your over thinking it.

Just do a buoyancy check - at the end of the dive - for changes of major items like suit or cylinders and record the amount of lead required for each.

If your floaty when shallow, there's every chance you're too light. Reinforced by you finning down at the start of a dive.

I don't adjust my weight just because I do or don't carry a touch and/or camera.

The first dive on any trip is a shake down to sort out issues like changed buoyancy.

 

[Edward3c]

Just noticed the "I don't like to add air to the BC".

At 10m (33') your wet suit will have lost half is buoyancy, the deeper you go the more it loses. If you don't compensate for the buoyancy lose your going to bounce along the bottom damaging the marine life. Another indication you're too light.

 

[The Chairman]

Just do a buoyancy check - at the end of the dive

You're overthinking it late.

Do a buoyancy check at the beginning of the dive. With legs, arms crossed, your BC empty and breathing on your reg, your head should be just awash. If you exhale, you should descend easily. Add a pound for every inch your head sticks out of the water. Repeat until your head is just awash.

 

[tursiops]

You're overthinking it late.

Do a buoyancy check at the beginning of the dive. With legs, arms crossed, your BC empty and breathing on your reg, your head should be just awash. If you exhale, you should descend easily. Add a pound for every inch your head sticks out of the water. Repeat until your head is just awash.

I know we've had his discussion before, but I still don't understand how this allows for losing 5-6 pounds of ballast when you tank gets empty. If your weighting is based on almost neutral at the beginning of a dive (what you describe sounds like about 1-2 pounds heavy), what happens at the end of the dive? Are you 3-4 pounds light?

 

[lowviz]

...//... Any help out there?

Yes, start here: Gear tips and recommendations

I hope to hell that Steve never sees this post, the sardonic grin would kill me from afar...

 

[ScubaJill]

ScubaJill,

Your over thinking it.

I'm posting this on Scubaboard. It seems to be the appropriate venue to ask diving questions that the average diver or dive instructor wouldn't care a whole lot about. Let's indulge me. I'm refining my thinking about buoyancy and I'd like to be more prepared for new situations.

Just do a buoyancy check - at the end of the dive - for changes of major items like suit or cylinders and record the amount of lead required for each.

And if I'm significantly overweighted? I'd rather figure this out on the front end and get within a range that's manageable. If it's refinement, that's fine, but I get a lot of advice about how much to add/subtract and it's mostly contradictory.

If your floaty when shallow, there's every chance you're too light. Reinforced by you finning down at the start of a dive.

I need to put on a few more pounds to get down on the first dive of the day. That weight, if I choose to add it, becomes noticeable later in the dive. I think it has something to do with the wetsuit and being dry. I don't have this issue when I dive without a wetsuit. Or dives later in the day. The shallow dives are a separate issue.

I don't adjust my weight just because I do or don't carry a touch and/or camera.

Mine can add up to 3-4 pounds. It's nice to know how negatively buoyant I am without additional weight.

The first dive on any trip is a shake down to sort out issues like changed buoyancy.

Well, not every group does a "shakedown dive." There's a whole thread about that. Anyway, I want to prevent wild swings in my weighting, particularly as I get into cold water diving. Being more methodical about it is going to help me in the short term to understand why things happen as they do. I work in research. I think about things. Then I tell people about the things I thought about.

Just noticed the "I don't like to add air to the BC".

At 10m (33') your wet suit will have lost half is buoyancy, the deeper you go the more it loses. If you don't compensate for the buoyancy lose your going to bounce along the bottom damaging the marine life. Another indication you're too light.

Well, I typically don't bounce along the bottom damaging marine life. I've got pretty good buoyancy and trim. My instructor emphasized to use the BC only as needed and not to compensate for being overweighted. I agree with him. It's nice to know how the changes in depth affect my buoyancy so I can deal with it without messing around with the BC. I like to use my breathing so I can get close to the reef and hover. When I have too much weight on, I simply cannot do this. Here, I'm guessing "too much" might be about 5 pounds over. When I need to add too much air into my BC (more than 1-2 puffs or so), the BC becomes the star of the dive. So my question about weighting refinement: do I add additional weight for a shallower dive, expecting that I won't experience neoprene compression? If it's going to be deeper than 30-40 feet, do I consider the weight I'll need for crushed neoprene? Do I always consider the weight of the tank at 500 PSI, even if I often come up with 1/2 a tank? Anyway, these are the questions I have, among others, which have led me to be more systematic in understanding my weighting.

You're overthinking it late.

Do a buoyancy check at the beginning of the dive. With legs, arms crossed, your BC empty and breathing on your reg, your head should be just awash. If you exhale, you should descend easily. Add a pound for every inch your head sticks out of the water. Repeat until your head is just awash.

Is this with an AL80 or some other tank? With a soaked wetsuit? I dropped a 5mm jacket into the water this weekend with 6 pounds of lead. It didn't budge even after 10 minutes. I was told to either add 9 pounds or nothing for it. Anyway, there's got to be a better way to do this than just guestimating all the time.

 

[Bob DBF]

I have a cheat sheet, but I only use one wetsuit, two BP/W's, and a number of different tanks. I do a weight check at 15', with 500# in the tank, and an empty BC to find my proper weight. I use the tank specifications if I use a different tank, but should I dive a new wetsuit, I'd have to make an estimate and do a real weight check at the end of the dive. It is an ongoing process.


Bob

 

[2airishuman]

To help me not make weighting decisions on the fly when I'm adding in new gear like a thicker wetsuit or a steel tank when I usually dive AL80s, I'm going to create a cheat sheet that I can laminate or put into a ziplock bag with the different variables I need to take into consideration when assessing how much weight I need to add on.

Hello Jill

I have a "cheat sheet" but it's pretty much a grid of exposure suit vs. configuration, like this:

----> No BC Singles Doubles
Rasher
3/2
3mm
7mm

Then if applicable I adjust for pony (stage) cylinders, and salt water.

Due to rounding and the overall imprecision of determining weighting, my chart can't quite be reduced to a formula. If I tried, it would be off by a couple of pounds here or there.

One of the problems to consider is that lead weights are typically somewhat underweight, and combined with that and the water they displace, their effect on buoyancy is only about 90% of their rated weight. Makes a difference if you're diving with 20# of lead.

 

[lermontov]

how many computations of gear assembly do you have to deal with? this should be straight forward if you diving similar conditions and configurations. I keep a note on my software logbook of gear and weights used etc so i can easily refer back to it if I'm diving similar situation, but as net doc suggests its not too much hassle to do buoyancy check when you get in and than ask the dive boat crew for an extra weight if you think you'll need it when tanks are empty.