saltwater vs fresh water

[FM1520]

When going from a swimming pool to the ocean, keeping all equipment and exposure protection the same, what is general rule for adding weight? I have heard 5 lbs, which sounds about right. Also, a lot of swimming pools around here use salt instead of chorine but not at the salinity level of the ocean - not sure if any difference in buoyancy.

Thanks,
FM

 

[Insta-Gator]

5 or 6 pounds to start off with for a buoyancy check. When making significant changes in gear or environment, it's always a good idea to do a buoyancy check.

Saltwater pools are not even close to ocean water.

 

[boulderjohn]

The primary factor in determining your weight needs is your exposure protection. If you wore a 3mm wet suit in the pool and then go to a warm water resort still wearing a 3mm suit, that is very different from going to a colder weather site with a 7mm suit or especially a 7mm Farmer John.

 

[PinkInkScuba]

You are correct in thinking ~5 lbs. As Insta-Gator mentioned, make sure you do a buoyancy check prior to your ocean dive and add or take away weight as needed. Most charters carry extra weight if needed.

 

[redacted]

FW has a density of 1.00. SW has a density of 1.027. So add 3% of the total weight of you and your gear to compensate for the difference in density. That is about 5 lb for most people.

 

[spectrum]

First off a saltwater pool that even approaches the salinity / specific gravity of ocean water is very rare so for this exercise consider it to be fresh.

You have established that ALL gear is going to be the same so that's that.

It comes down to the stated difference in specific gravity so unless your someplace really odd like the Dead Sea the 3% of total dry diver weight is what you are looking at. This is your total weight before you jump into the water, you suit, equipment, full cylinder, weights, everything.

Keep in mind that your excitement, surge, current and a host of other factors including discrepancies in your prior weight check can all effect the end result. Add the 3% and try to bring some as small weights that are clipped on or in accesible pockets. Near the end of the dive in 10-15 feet of water with your cylinder near 500 PSI and your BC empty of air you can hand off small amounts of weight. You will know when you get too light, take that last piece back and you have a really dialed in number.

Pete

 

[BRT]

FW has a density of 1.00. SW has a density of 1.027. So add 3% of the total weight of you and your gear to compensate for the difference in density. That is about 5 lb for most people.

Adding 2.5% of total weight in identical equipment has worked well for us going from fresh to salt water but for me that is close to 8 pounds in a drysuit.

 

[spectrum]

One of the funny quirks of this is that when you add lead to account for the change in water that lead also displaces some water and the net adjustment is less than the gross weight added. Since 2.5% is already a slight round down in many cases this displacement can cause you to come up short, especially as the diver gets heavier. This is the basis of suggesting 3%. A diver is much better off adusting to a slightly "heavy" value then tuning at a weight check than to go in under weighted.

 

[adutto]

You should always do a buoyancy check, it is the only way you will feel 100% sure the wighting is ok.

Happy diving!

 

[Necklinsberg]

A factor to consider that I don't think I saw up thread ...

-- If you only do your buoyancy check at the beginning of the dive, be sure to add some extra weight to offset the air consumed (about 6 pounds for an 80). If you are 'just good' at the beginning of the dive, you will probably be floaty at the end

Even if you had weight check at the end of one of your pool dives, it is unlikely that you pulled the tank down to 500 psi. You probably will end up sucking down all of your air on the first couple of dives so you need to account for that additional air consumption

Be sure to discuss this with your instruction.