Fresh Water vs. Salt Water - Wt.'s?

[MN Lakeman]

I've been diving several years cold, fresh water diving here in MN. 'Have a great opportunity to dive Puget Sound next week. I currently dive w/ an O'Neill 7m + 5M J3000 wetsuit, & 22 lbs. - any estimates out there as to what I'll need to bump up to for salt water?

 

[TSandM]

General rule of thumb is to add 2.5% of the total weight of diver and gear.

 

[markfm]

It's based on the density difference between salt and fresh water. If you're perfectly weighted in fresh, and take the same setup (wetsuit, tank,...) to salt, you're dealing with the density difference -- 62.4 (fresh) vs 64 (salt) pounds per cubic foot.

The value for salt is the norm -- you can find some locales with different density, perhaps right where a river lets into the ocean (mixing).

 

[spectrum]

Another easy way to make the same calculation is to take the total dry diver weight (you, all of your gear, weights, tank) just as you will be before getting wet and divide by 40. As an example if you tally up at 320 pounds then add 8 for the ocean. Removing weight for going to fresh water is done in just the same way.

This is physics and if your baseline weight is correct that's the whole story.

Well, maybe not the whole story.... In some situations I have seen freshwater divers want to have a couple of extra pounds in order to stay down better in ocean surge. Compared to most freshwater you are more likely to find yourself in upwelling and other turbulence in salt water.

Pete

 

[MN Lakeman]

Using TsandM & Spectrum's formula, both come out about the same - 5 more lbs. Thanks!

 

[Charlie99]

Using TsandM & Spectrum's formula, both come out about the same - 5 more lbs. Thanks!

Just remember that the 2.5% or 1 pound per 40 pounds are for the TOTAL dive weight, including the weight of the near empty tank, BCD, your lead, and any other gear. Since the weight of tank + gear + 33 pounds of lead is likely to be up around 70 or 80 pounds, a 5 pound adjustment is adequate only if you yourself weigh in the 120 to 130 pound range.

That's why the other recommendation often given for a fresh to salt adjustment is just "add 6 pounds", since that's appropriate for a typical single tank diver that weighs about 170 pounds without gear.

It's better to be 1 or 2 pounds heavy than to be too light.

 

[MN Lakeman]

Just remember that the 2.5% or 1 pound per 40 pounds are for the TOTAL dive weight, including the weight of the near empty tank, BCD, your lead, and any other gear. Since the weight of tank + gear + 33 pounds of lead is likely to be up around 70 or 80 pounds, a 5 pound adjustment is adequate only if you yourself weigh in the 120 to 130 pound range.

That's why the other recommendation often given for a fresh to salt adjustment is just "add 6 pounds", since that's appropriate for a typical single tank diver that weighs about 170 pounds without gear.

It's better to be 1 or 2 pounds heavy than to be too light.

I've focused for 7 years to have primo buoyancy, & over that time had shed unnecessary wt. At 160 lbs, 9% body fat, I'll try 5 more lbs. & go from there. Thanx -

 

[RS]

I've focused for 7 years to have primo buoyancy, & over that time had shed unnecessary wt. At 160 lbs, 9% body fat, I'll try 5 more lbs. & go from there. Thanx -

let us know how it works out.