1st salt water dives vs weights

[strawhouse]

Looking for a little info on the comparison between my weight use during my salt water dives vs my fresh water dives. I went into my LDS to ask him what he thought of this and he seemed not too interested or he didnt care. So here I go:

During either dives I use the same mask, flippers, boots, snorkel, and BC
Im 6'3 240 LBS ( if anyone cares )

Fresh water:
Farmer John 7mm with a 3/4 7mm suit over top
80 Aluminum tank
5mm hood
7mm gloves
43 LBS of lead

Salt water
3mm farmer john
reef gloves
steel tank ( I dont know the size but it was shorter than the aluminum 80 but fatter, it was filled to 3000psi and I seemed to get the same amount of time out of the one tank as I do on the aluminum 80)
12 LBS of lead

Is the amount of lead between the two a normal amount of difference? Or how much of this is to do with the steel tank? Or have I been able to loose weight because of being more comfortable with diving? Really looking for someone to help me out with figuring this out because I feel a little confused after talking to the LDS

Thanks

 

[redacted]

Looking for a little info on the comparison between my weight use during my salt water dives vs my fresh water dives. I went into my LDS to ask him what he thought of this and he seemed not too interested or he didnt care. So here I go:

During either dives I use the same mask, flippers, boots, snorkel, and BC
Im 6'3 240 LBS ( if anyone cares )

Fresh water:
Farmer John 7mm with a 3/4 7mm suit over top
80 Aluminum tank
5mm hood
7mm gloves
43 LBS of lead

Salt water
3mm farmer john
reef gloves
steel tank ( I dont know the size but it was shorter than the aluminum 80 but fatter, it was filled to 3000psi and I seemed to get the same amount of time out of the one tank as I do on the aluminum 80)
12 LBS of lead

Is the amount of lead between the two a normal amount of difference? Or how much of this is to do with the steel tank? Or have I been able to loose weight because of being more comfortable with diving? Really looking for someone to help me out with figuring this out because I feel a little confused after talking to the LDS

Thanks

Lots of variables there but al tank and 7mm 2-piece is a lot of floaty stuff.

SW takes more weight than FW but the 3mm and steel is a big decrease in floaty stuff. All else equal, which it is not, your body weight and gear probably accounts for an 8 lb increase in SW compared to FW.

I don't see any obvious conflict.

a

 

[vladimir]

The specific density of saltwater is approximately 1.025 (it varies a little from place to place). Take the weight of you and your equipment (including lead) when you are neutrally buoyant in freshwater and multiply by 1.025 to get your total weight in saltwater. Add lead to achieve that figure. To the extent that your equpment changes, your buoyancy may differ.

 

[njedrn]

In fresh water with a farmer john (7mm) and 3/4 (7mm) I used 32lbs with an alum tank.
In salt water, with a 3mm full wetsuit I use 20lbs with an alum tank.
I weigh about 300.

So there was a significant difference for me, even being comfortable in the water with 20+ dives in both environments.

 

[boulderjohn]

Fresh water:
Farmer John 7mm with a 3/4 7mm suit over top
80 Aluminum tank
5mm hood
7mm gloves
43 LBS of lead

Salt water
3mm farmer john
reef gloves
steel tank ( I dont know the size but it was shorter than the aluminum 80 but fatter, it was filled to 3000psi and I seemed to get the same amount of time out of the one tank as I do on the aluminum 80)
12 LBS of lead

Am I understanding the first part correctly? Do you have 21 mm of neoprene on your core in fresh water?

If so, that's a lot of rubber. I have never seen anyone in that much neoprene, so it is hard for me to judge what is normal. If you were just wearing a 7mm farmer john and all the rest, I would have guessed that you are very much overweighted in fresh water. We are all different, though, so I would be guessing to begin with,. If you really are wearing 21 on the core, then I don't even want to guess what is right.

Your salt water weighting seems pretty reasonable to me.

The effect of layers of neoprene on buoyancy is HUGE.

 

[pasley]

So lets review.
Freshwater 7mm Farmer John & AL80= 43 Pounds of lead. 43 Pounds!
Salt Water 3mm, Steel tank(unknown size and mfg) =12 pounds of lead. (that sounds about right for 3mm salt water).
Difference of 31 pounds.

Equipment changes account for some of the difference but certainly not all.
Steel Tank of unknown size or manufacture Vs AL80 - Assuming a Steel 80 -4 pounds.
7mm Farmer John Vs 3mm Farmer John (they make 3mm farmer johns?)-8 pounds.
Total in equipment changes - 12 pounds.
Freshwater to Salt Water a change of about 2.5% or about 1 pound.

That leaves 18 pounds unaccounted for. Normally in salt water, 240 lb person in 7mm suit AL80 tank would be expected to wear about 24 pounds (plus or minus a tad) not 43 pounds. 24+18=42 I find the 43 pounds suspect.

I would suggest doing a dive and re-checking your weight. Drain the tank to <1000 PSI (500PSI preferred) and checking your buoyancy at 15 feet.

End of the day there are many changes here but not sufficient to account for a shift of 31 pounds. Example: I am 6 ft, 145 lbs shift from 7mm AL80 Saltwater to 3mm AL80 Saltwater was -8 pounds. You need a bit more lead in salt water than in fresh water (2.5%) but that is only a few pounds and your farmer john will use more lead too. As njedrn said, at 300 pounds in saltwater 7mm he is using 32 pounds of lead. I would anticipate you would use less, not more. But each person is different.

 

[TSandM]

Lots of things changing between the two setups.

My 3 mil wetsuit is about four lbs positive (one for your size would be a couple more). I have read that a new 7 mil wetsuit can lose 20 lbs of buoyancy, and you've got doubled layers on your midsection, so it's probably even more. So there would be 15 pounds or so of difference. The heavy hood is a pound or two as well.

An Al80 is four pounds positive at the end of the dive; most steels are at least 1 pound negative. So there are five more pounds.

On the other hand, assuming you're around 300 lbs with all your gear, you need to add about 7.5 lbs to go from fresh to salt water.

So the magnitude of the difference you're describing isn't completely out of line. Heavy exposure protection means lots of lead! OTOH, if those fresh water dives were your certification dives, you may have been overweighted a bit there. It's common with students, because they have so much difficulty descending the first few times.

 

[Bob DBF]

There is a HUGE difference in buoyancy between a 3mm one piece (never heard of a 3mm Farmer John).

Diving the CA north coast you need insulation, last couple of dives were 50 degrees and it gets marginally better at other times. I wear a 7mm Farmer John, step in 7mm jacket, 7mm gloves, 7mm/5mm cold water hood, 7mm hard sole boots. At 6' 215# it takes 34# of lead to make me neutral at 15' with no gear, for abalone diving. That neoprene floats good!

With a Jacket BC and a steel tank I use 37#, add another 5# or so for AL.

At this point you can see one reason why I am putting together a BP/W this year.

Bob

 

[moneysavr]

As said,
Get in the pool with farmer and your AL 80 start with 1000psi get down burp the air out of the wet suit add lead till with your BC/wing is drained of all air you should be eye level in the water if leaded close,I think you as said are over leaded with 43lbs man you got to have pockets and weight belt full,
now with the 3 mm steel 80 you seem close,
my thoughts get your weight down with the farmer, try diving steel tanks once you do you will never go back to AL's and try a steel tank to dive with the farmer 80,100 you can drop some lead and like the end of dive characteristics.
dive safe

 

[Bubbletrubble]

There is no substitute for doing a proper weight check.
You've changed around too many variables (different exposure protection, unknown change in tank) for any of our rule-of-thumb calculations to be helpful. The best thing you can do is conduct a weight check with all of the appropriate gear when you arrive at your salt water dive destination. It should only take a couple of minutes. No big deal.
It's surprising that many divers don't know how to do a proper weight check. Being properly weighting is an important safety issue. Don't take it lightly. (pun intended)
If you are unsure about how to do a weight check, please consult your OW training manual. It's in there.
The 31 lb. lead difference you describe seems quite extreme, but so long as you did an accurate weight check in each gear configuration/condition, it's correct.

Have a great trip!