weighting- freshwater vs. seawater

[sandanbob]

Thank you for the replies. I did over simplify, and I think I know where the error was in the process. The diver and gear would displace a specific volume, at a given total weight, and that would be used (if going that route) to determine the weight needed to counteract the difference.

However, my initial calculation was only looking at the portion that would have been above the surface without the extra weight, as the rest would have been submerged, whatever portion that would be.

When looking at the diver (and gear) as a whole, then the difference in densities of the two types of water make the larger difference as mentioned by other posters.

Does that sound right?

 

[boulderjohn]

The dive buddy calculator, like pretty much all online calculators I have ever tried, tells me I need more than double the weight I actually need.

 

[OrcasC205]

The dive buddy calculator, like pretty much all online calculators I have ever tried, tells me I need more than double the weight I actually need.

You must be pretty dense -- no pun or slight intended.

 

[happy-diver]

No pun now that is funny and considering you have directed it at one of the denizens of the forum
with backroom sympathies
courageous too

Anyone thinking that half a pound is of any consequence at all
unless you are at the top of the buoyancy game and diving in
still water will get a shock if exposed to the oceans elements

 

[CT-Rich]

The dive buddy calculator, like pretty much all online calculators I have ever tried, tells me I need more than double the weight I actually need.

Some of us are softer and doughyer than others, I suppose. YMMV.

 

[boulderjohn]

Some of us are softer and doughyer than others, I suppose. YMMV.

I am softer and doughyer than I would like to be.

I think a key factor not included in sites like that is BCD type. A recent packing error for a trip forced me to rent and wear a jacket BCD in the ocean for the first time since I started diving. I needed far more weight than I would normally use because of its increase bulk. I had to use 12 pounds, which is much more than I needed even back when I used a back inflate BCD (8 pounds). I felt like I was diving with an inner tube around my waist. Even so, dive buddy said I needed 21 pounds.

 

[James79]

The best results for any calculator I've had are the Buoyancy Computer spreadsheet that RSingler wrote; Info - Optimal Buoyancy Computer . As I understand it, it is mostly formulas for pure physics, with some estimates and empirical data thrown in (like compression rates for neoprene). I have the luxury of a small pool in the back yard, so I initially worked the spreadsheet from both ends. I verified my rig is neutral in freshwater by itself in the pool, put in estimates for the reg, told it what tank I had and then adjusted my "personal buoyancy" until the lead required matched what I actually needed. Once I had that in, I've used it to calculate needed lead for wetsuits, changes from salt to fresh water, and different tanks and it's always been within a pound or so.

Respectfully,

James

 

[boulderjohn]

A little more data:

If the wind ever stops blowing here, I will dive again. I went to Dive Buddy and put in the data for the dive I plan to do with the equipment I plan to use. With my 5mm suit and steel tank in the ocean, it says I need 19 pounds.

I will count my steel backplate as 6 pounds. I will carry no weight whatsoever, and I will be a little overweighted.