Fresh to Saltwater - nothing else changes - how much more weight???

[djanni]

Going from fresh to saltwater. Nothing else will change. How much more weight will I need?

 

[RonFrank]

Going from fresh to saltwater. Nothing else will change. How much more weight will I need?

General guideline is about 6lbs. I dive 10lbs fresh in a 3mm, and 16lbs salt.

 

[craborn]

six pounds is about right but when you get there do a shore dive/ weight check ... have fun clay

 

[gecko3s]

At the risk of being redundant...six worked for me too... I was diving 12lbs in the springs, and when I went to salt, I also happened to have just gotten a bp/w setup, with a stainless steel backplate that ways, I think, 6 1/2 pounds or so... I kept my 12lbs and with the extra six found that I was pretty well weighted.

 

[pickens_46929]

Going from fresh to saltwater. Nothing else will change. How much more weight will I need?

It's relative to the amount you use to begin with... if you think about it... seawater weighs only slight more than fresh water... so I use 1# add'l for every 5#'s you use in fresh water... so I use about 8# in fresh with a AL80 Neutral and a full 3mm... I can get by with 10# in salt water with the same setup.

However, if I am using 5mm full... I use 15# in fresh and 18# in salt water.

Be careful to check to double check the tank... made a dive recently in Key Largo and got a regular AL80 instead of a neutral AL80... had a hard time getting down...

Also, it's best to err on the side of being slightly heavy to start with and work on dropping the weight throughout the trip. So if I go to Key Largo the first trip of the year after not doing salt water for a while, I maybe start with 12# and after a day or so am down to 10#.

 

[markfm]

The six is about the norm. It's about 2.5% of your total dry (land) weight, 1 pound for every 40.

Example:
Me on scale, geared up (no tank) and holding my fins: 200 pounds
Empty AL80, with valve: 34 pounds
Fresh water weights: 4 pounds
Total weight: 238 pounds -- pretty close to 240. 240/40 = 6 lbs = what I add.

 

[Charlie99]

It's relative to the amount you use to begin with... if you think about it... seawater weighs only slight more than fresh water... so I use 1# add'l for every 5#'s you use in fresh water... .

What counts is your TOTAL weight, not how much lead you are carrying. As other posters have stated, the difference in density between salt and fresh water is around 2.5%, so you have to add that amount of weight.

2.5% is the same as 1/40, or 1 additional pound for every 40 pounds of dry land weight (of you + your gear including tanks and lead)

Since 190 pound of me + 50 pounds of gear is about 240 pounds, the posters that say "add 6 pounds" are also saying the same thing, but just jumping to the final answer that works for most people.

-----------------

Since it's better to be a pound or two overweight than a pound or two light, when going from fresh to salt I'd start off with 7 extra pounds for the 1st dive, and then adjust. Going the other way, dropping only 5 pounds when going to fresh should work for the 1st dive.

 

[ScubaSarus]

I use a 4# differential. It also dependent on the mass of the gear thats causing the bouyancy changes and your boddy mass. If you are a big person with a new wetsuit (very bouyant) I'de lean more towards 6#.

 

[Rick Murchison]

Charlie99 is correct. The change in buoyancy from fresh to salt water has absolutely nothing to do with how much lead you need in fresh water and is strictly dependent on your total weight.
Now, if that's the physics - and immutable fact - why does Pickens feel that he's properly weighted with only a two or three pound addition when moving from fresh water to salt? Obviously there's some disconnect here... either he's overweighting for fresh water or underweighting for salt, or a little of both.
There's nothing unusual about Pickens' conclusion, by the way. It's one of those "common knowledge" thingies that seems to have a life of its own, but
Why?
Usually (and Pickens will have to tell us if this is right in his case) it has to do with differences in the way - the methods - in fresh and salt water diving. Most recreational divers are in one of two situations. (or both)
(1) Their fresh water diving is in relatively cold water, and their salt water diving is in the tropics, so the exposure protection worn is very different from one to the other and there isn't any direct weighting equivalent that's relevant.
(2) Their fresh water diving doesn't involve a boat, and their salt water diving does. In this case the descent and ascent in fresh water will be "free", while salt water most likely involves the use of an anchor or down line as an assist, and there's some surge from the waves above, which combine to mask any slight underweighting near the surface. On the bottom it doesn't matter, since with even a 3 mil wetsuit you'd have to be grossly underweighted to realize you need more lead.
---
There's also the possibility that Pickens is diving in low-salinity "salt" water (a bay?) and that his two-three pounds is correct for his situation.
Rick

 

[pickens_46929]

Charlie99 is correct. The change in buoyancy from fresh to salt water has absolutely nothing to do with how much lead you need in fresh water and is strictly dependent on your total weight.

Yep... total weight.

Now, if that's the physics - and immutable fact - why does Pickens feel that he's properly weighted with only a two or three pound addition when moving from fresh water to salt? Obviously there's some disconnect here... either he's overweighting for fresh water or underweighting for salt, or a little of both.

lol... nope... just a really skinny dude! So yeah, 2.5% of *total* weight is about right.

There's nothing unusual about Pickens' conclusion, by the way. It's one of those "common knowledge" thingies that seems to have a life of its own, but
Why?

Because it's easier to figure 1# for every... than 2.5% of total weight.

Usually (and Pickens will have to tell us if this is right in his case) it has to do with differences in the way - the methods - in fresh and salt water diving. Most recreational divers are in one of two situations. (or both)
(1) Their fresh water diving is in relatively cold water, and their salt water diving is in the tropics, so the exposure protection worn is very different from one to the other and there isn't any direct weighting equivalent that's relevant.

True... but if you dive around the Northeast or even mid-atlantic... it's drysuit all year around. I do tend to dive in both fresh water Florida springs (72 F) in 3mm / 5mm full and also then in the Keys in winter when I need a full 3mm / 5mm as well.

So as long as the equipment stays the same... minute you change pieces of gear, like using a *brand new* wetsuit instead of that old one...

(2) Their fresh water diving doesn't involve a boat, and their salt water diving does. In this case the descent and ascent in fresh water will be "free", while salt water most likely involves the use of an anchor or down line as an assist, and there's some surge from the waves above, which combine to mask any slight underweighting near the surface. On the bottom it doesn't matter, since with even a 3 mil wetsuit you'd have to be grossly underweighted to realize you need more lead.

In the Keys I don't use a line and most of my descents / ascents are just like fresh water.

Did discover though in my recent Cavern class that even my 3mm full has 2# of bouyancy change between the surface and 20' deep...

Dave
---
There's also the possibility that Pickens is diving in low-salinity "salt" water (a bay?) and that his two-three pounds is correct for his situation.
Rick[/QUOTE]