Bouyancy: Warm water vs Cold water

[tzeilstra]

I just read that cold water weighs more than warm water. This makes sense, as molecules condense at lower temperatures. But it got me to thinking...if cold water is heavier, wouldn't you be more bouyant in cold water than you would in warm water, all other things being equal? This topic was never addressed in my OW or AOW classes, so maybe the difference is too minute to consider. But has anybody had any experience with this or heard of this?

 

[scubadobadoo]

The temp of the water has no impact on my personal buoyancy. Going from a 3m shorty to a dry suit and other cold water gear does have an impact.

 

[divingtigger]

Is there a chart somewhere that will indicate the amount of weight needed for salt water dives?

 

[Blackwood]

I just read that cold water weighs more than warm water. This makes sense, as molecules condense at lower temperatures. But it got me to thinking...if cold water is heavier, wouldn't you be more bouyant in cold water than you would in warm water, all other things being equal? This topic was never addressed in my OW or AOW classes, so maybe the difference is too minute to consider. But has anybody had any experience with this or heard of this?

Well, yes, but the density change of water within dive-able temperatures is negligible.

For example, taking two extremes: water at 33.8°F is only 0.43% more dense than water at 86°F. So if you make 50 pounds of buoyancy in the tropics, you'll make 50.2 pounds in the arctic.

Similarly, water isn't really incompressible as dive text claim. Its density does increase with depth. But not by enough to consider it.

Is there a chart somewhere that will indicate the amount of weight needed for salt water dives?

No.

 

[boat sju]

tigger,

The short answer is, you'll probably need APPROXIMATELY 6 lbs more weight in saltwater.

 

[Charlie99]

The long answer is ---- Saltwater is about 2.5% more dense than freshwater. If you use exactly the same gear, then a pretty close adjustment in weighting when moving to saltwater is to add 2.5% of your TOTAL dive weight. By total dive weight I mean the total weight of you, and all of your gear including weightbelt and the tank. Since 2.5% is the same as 1/40, another way this rule is stated is to "add 1 pound of lead for every 40 pounds of total dive weight".

For the typical single tank diver of 180 pounds body weight and 60 pounds gear their total weight is 240 pounds and the salt to freshwater adjustment is 6 pounds, which why Retro's short answer of "6 pounds" works.

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Using the same sort of calculations and the 0.43% number Blackwood supplied above, a diver with 240 pounds total dive weight would add 1 pound of lead when changing from 86F water to 32F water. Of course, this 1 pound adjustment applies only if you use the same thermal protection in 86F and 32F water, which is highly unlikely.

 

[Blackwood]

I'm interpreting divingtigger's question differently.

He didn't mention anything about going from fresh to salt, so I assumed he wanted a table detailing weight requirements for various configurations.

Of course, this 1 pound adjustment applies only if you use the same thermal protection in 86F and 32F water, which is highly unlikely.

MAN UP!



Of course, that adjustment also assumes that you displace the same volume of water. But if we're treating water as compressible...

 

[Bobyjimmie]

....um warm water means less neoprene = less buouyancy. Cold water means more neoprene or drysuit = more buouancy so who cares the density either way you gotta compensate right?

 

[Gary D.]

If the water gets cold enough you can eliminate weights all together.

Gary D.

 

[solensdotter]

As the previous posters have already mentioned, the big difference regarding weighting with colder water is going to be the increased thermal protection. The neoprene and/or air in the dry suit are very buoyant and need to be compensated for through increased weight.