Freshwater is less dense than Saltwater, hence the pressure for a given depth should be lower for freshwater than saltwater.
Do freedivers prefer to dive in freshwater?
Do freedivers prefer to dive in freshwater?
-
Welcome to the DeeperBlue.com Forums, the largest online community dedicated to Freediving, Scuba Diving and Spearfishing. To gain full access to the DeeperBlue.com Forums you must register for a free account. As a registered member you will be able to:
- Join over 47,943+ fellow diving enthusiasts from around the world on this forum
- Participate in and browse from over 531,990+ posts.
- Communicate privately with other divers from around the world.
- Post your own photos or view from 7,455+ user submitted images.
- All this and much more...
You can gain access to all this absolutely free when you register for an account, so sign up today!
Freshwater vs Saltwater
- Thread starter lisabeeren
- Start date
Thread Status: Hello
, There was no answer in this thread for more than 90 days.
It can take a long time to get an up-to-date response or contact with relevant users.
It can take a long time to get an up-to-date response or contact with relevant users.
I dive in both freshwater and saltwater. What it means it you are using slightly less weight in freshwater. You still have to balance your weight. If you used the same weight as saltwater you would get down easy but would have a harder time getting up.
The pressure changes are still happening at the same point in both saltwater and freshwater to my knowledge.
The pressure changes are still happening at the same point in both saltwater and freshwater to my knowledge.
I've heard, but haven't noticed, that free immersion is easier in fresh water due to lack of density, and that constant ballast is easier in salt water- more solid substance for the blade to push against.
I prefer fresh water because it tastes better as well, but salt water has cooler stuff to look at.
Jon
I prefer fresh water because it tastes better as well, but salt water has cooler stuff to look at.
Jon
Fresh water is supposed to be less viscous, so less friction. It certainly feels to me like it is slicker, and faster going down. My fresh water diving is in places that do not allow a straight uninterrupted desent, so I can't test the feeling.
It also makes a difference in depth guage accuracy. Most guages are calibrated for salt water and slightly underestimate depth in fresh. I thought the difference was about 3 per cent, which gets significant when diving 30 m or so and doesn't square with Tompa, but I could be wrong. Anybody else have an estimate?
Connor
It also makes a difference in depth guage accuracy. Most guages are calibrated for salt water and slightly underestimate depth in fresh. I thought the difference was about 3 per cent, which gets significant when diving 30 m or so and doesn't square with Tompa, but I could be wrong. Anybody else have an estimate?
Connor
Interesting topic. The figures you see used are 62.5# for a cubic foot for fresh and 64 for salt water. For open ocean and distilled water they seem to be very close. The other factor though, is temperature. I think that water density is inversely proportionate to temp and 15 degree fresh water is denser than 25 degree salt water. The pool in town measures over 1.01 and the Pacific about 1.025 depending on the rain and tide. Trial and error methods from way back came up with 5-6# of lead difference between lake and ocean. Viscosity is probably another factor. Even very cold fresh water feels slippery compared to salt. Depth guages correct for temperature, too.
I repeat, interesting subject without even talking about water's magical property as the temp approaches zero.
Sorry about mixing up the two systems of measurement.
Aloha
Bill
I repeat, interesting subject without even talking about water's magical property as the temp approaches zero.
Sorry about mixing up the two systems of measurement.
Aloha
Bill
As for the influence of density and viscosity on the speed of swimming - I saw once a beautiful article, describing a test made by one US university team. First they measured the swimming times at a group of people of different swimming skill levels (from quite bad swimmers to excelling swimming competitors) in the university swimming pool. Then they filled the full 25m swimming pool with agar jelly (if I remember well, they used something like 200kg of agar-agar powder) and repeated the speed test with the same swimmers again. I am not sure now if they tested also fin swimmers.
The results were rather surprising - the times were practically identical in both cases. So although the bigger viscosity and density slow you down more, they also give better support for the forward motion. So from this point of view, lower viscosity can be indeed of some advantage for Free Immersion (where the better support of the water viscosity offers is unimportant for the propulsion). In contrary, for self-propulsing disciplines (with and without fins), the influence of higher density/viscosity for better support should eliminate itself by higher resistance/friction.
Unfortunately I am unable to find the article again now - I certainly use wrong keywords. I bet the article is rather well ranked in Google.
There is another aspect that makes difference in salt- and fresh-water diving - the buoyancy difference at the surface and at the bottom. Especially if you use compressible wetsuit, the differece will be greater in salt water, hence you will need to fight it more during the descent or ascent, or during both (depends on your weighting).
The results were rather surprising - the times were practically identical in both cases. So although the bigger viscosity and density slow you down more, they also give better support for the forward motion. So from this point of view, lower viscosity can be indeed of some advantage for Free Immersion (where the better support of the water viscosity offers is unimportant for the propulsion). In contrary, for self-propulsing disciplines (with and without fins), the influence of higher density/viscosity for better support should eliminate itself by higher resistance/friction.
Unfortunately I am unable to find the article again now - I certainly use wrong keywords. I bet the article is rather well ranked in Google.
There is another aspect that makes difference in salt- and fresh-water diving - the buoyancy difference at the surface and at the bottom. Especially if you use compressible wetsuit, the differece will be greater in salt water, hence you will need to fight it more during the descent or ascent, or during both (depends on your weighting).
Last edited:
