Help with Buoyancy Math

[SPG3K]

Ok, I know this will not be an exact science since no one here is me, but I need some basic help so I can buy the right amount of stuff.

I currently own 14lbs of weight in 4's, 2's, 1's. (2 each)

My usual gear for the quarry here has been 10lbs of weight with a 3mm Pinnacle Breaker.

I'm headed to Florida this weekend, and my Breaker is still in California for repairs to a tear in the leg of the suit.

I'm going to pick up a 1mm Akona this morning to take with me, and I'm curious if there is a decent means with which to calculate how much weight I will need to add or drop with the change to salt water and to a 1mm suit.

If I need more, I'd like to buy it here where its cheap.

 

[Walter]

Get in the water and switch weights around until you float at eye level with full lungs and an empty BC. If you do this with a full AL 80, add 6 lbs to compensate for the air you'll use over the course of your dive. Any time you use a new equipment configuration, you'll need to check your weighting in the water.

 

[scubadiver888]

Ok, I know this will not be an exact science since no one here is me, but I need some basic help so I can buy the right amount of stuff.

I currently own 14lbs of weight in 4's, 2's, 1's. (2 each)

My usual gear for the quarry here has been 10lbs of weight with a 3mm Pinnacle Breaker.

I'm headed to Florida this weekend, and my Breaker is still in California for repairs to a tear in the leg of the suit.

I'm going to pick up a 1mm Akona this morning to take with me, and I'm curious if there is a decent means with which to calculate how much weight I will need to add or drop with the change to salt water and to a 1mm suit.

If I need more, I'd like to buy it here where its cheap.

Some of the more experienced divers might be able to help you if you give your height and weight. The general rule of thumb is based on weight. However, more fat equals more weight, i.e. if you are short and heavy you probably need more weight. If you are trim and fit you will be less buoyant.

Less Neoprene means you will float less. Salt water means you will float more. If it was just going from 3mm to 1mm I'd guess you can drop 6lbs. Going from fresh water to salt water I'd guess you can add 5lbs.

So a wild guess would be drop a pound or stay at 10lbs.

 

[SPG3K]

I don't know when I will have time to do that, but for what it's worth - I did think of that first. Unless the charter folks are willing to let me play around for a minute before we start the dive.

Hopefully they will allow me a minute. If not, I guess I will just have to make a best guess for the first tank and correct on the second tank. Assuming 6 extra lbs for the tank, would that mean I need to use 5-6 for the saltwater, and 6 for the tank? Taking my total to 22lbs (Minus my guess of 4 for the suit, someone else said 6, so, 16 lbs, ish?)

We're getting into Destin around midnight Thursday, diving 8 am Friday. Otherwise I'd just hop in the surf at low tide and check it out, but I don't think I will have time.

 

[SPG3K]

Some of the more experienced divers might be able to help you if you give your height and weight. The general rule of thumb is based on weight. However, more fat equals more weight, i.e. if you are short and heavy you probably need more weight. If you are trim and fit you will be less buoyant.

Less Neoprene means you will float less. Salt water means you will float more. If it was just going from 3mm to 1mm I'd guess you can drop 6lbs. Going from fresh water to salt water I'd guess you can add 5lbs.

So a wild guess would be drop a pound or stay at 10lbs.

I'm 5'9" - 185-190 depending on the week, lol.

 

[Walter]

If you were going to use the exact same equipment, you could take the weight of it (including lead) and you (190 + 50 {a wild guess} = 240), multiply by .024 (5.76 in the example, so add 6 lbs) and add that amount to your lead. That would be a total of 16 lbs, not 22. Since you'll be switching from a 3 mm suit to a 1 mm suit, you'll need less. If you can weight yourself in a pool with the new suit before the trip, you can get it exactly if you know the total weight (dry weight). Your height isn't an issue.

 

[dkktsunami]

A guesstimate for your salt water weighting in 1 mil, based on info given, would be appx. 12 lbs. Eventually you should be able to drop a couple more pounds. Start with 12lbs. and do a buoyancy check. Have fun.

 

[redacted]

I like to measure the buoyancy of all my neoprene to make these kind of switches a bit easier. So lets make some estimates:

Lg 3mm jumpsuit is about 7lb buoyant.
Lg 1mm jumpsuit is about 2lb buoyant.

So in FW your wetsuit change would drop you to 5 lb lead.

Assuming you and your gear weight in at about 250 and adding 3% for the change to SW, that's another 8 lbs.

So you should be good with 13 lb. But since overweight is more manageable than under, why not load up all 14 lbs and then adjust from there after the first dive.

 

[Charlie99]

I like to measure the buoyancy of all my neoprene to make these kind of switches a bit easier. So lets make some estimates:

Lg 3mm jumpsuit is about 7lb buoyant.
Lg 1mm jumpsuit is about 2lb buoyant.

So in FW your wetsuit change would drop you to 5 lb lead.

Assuming you and your gear weight in at about 250 and adding 3% for the change to SW, that's another 8 lbs.

So you should be good with 13 lb. But since overweight is more manageable than under, why not load up all 14 lbs and then adjust from there after the first dive.

I'm about his weight and find 6 pounds is just right for fresh to saltwater adjustment and have found that my wetsuits are around 2 to 3 pounds of buoyancy per millimeter so my best guess would be +6-5= add 1 pound. Since being a couple pounds overweighted is much less hassle than being underweighted, I'd add a couple pounds just to be safe. So +3 on his current 10 pounds gets me to the same 13 pound recommendation as you, but I'm guessing that this will most likely make him a couple of pounds overweighted.

THIS ASSUMES THAT THE ORIGINAL POSTER'S ORIGINAL WEIGHTING WAS WITH AN AL80. Otherwise, he needs to make an additional adjustment for the change in type of tank.

 

[Buoyant1]

I seem to use the same amount with my 3mm in salt water that I use with my 7mm in fresh water. (although I really need to do a buoyancy check in both)