Salt - impact on weights?

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The points about the salinity are true. What does complicate an exact comparison ("why X kg more instead of only Y kg according to maths?") is probably that other factors (equipment, tank, dive profile) will typically change when on travel...
 
Ahh.. Now i get it, I think...

Your math is correct, @stepfen but you calculate a percent increase of added weignt (lead). The 1 % or 3.5 % is a persentage of the total weight.

So, yeah, you'll need ~3.5% of your total weight in lead in the Red Sea than in freshwater whereas you'll only need ~2.5% for typical ocean diving.
I am pretty sure @victorzamora means 3,5 % of total weight (3,5 kg if diver is 100kg), and that this will have to be added as lead. Not 3,5 % of your total lead weight.

Calculating a percentage of added weight will never work as a rule of thumb. If I jump in the pool wearing nothing I am more or less neutral. If I jump in the read sea I need a little over 3 kg to get neutral. That is an infinite increase in added weight, but 3.5% added to the total weight.

Please note that the wearing nothing part of the explanation is only for accademic purposes. :wink:Out of respect for fellow divers and local culture I would add a speedo to that test.
 
Please note that the wearing nothing part of the explanation is only for accademic purposes. :wink:Out of respect for fellow divers and local culture I would add a speedo to that test.
Speedos??? I thought it's considered much better to wear nothing than wearing speedos, at least on the west side of the Atlantic.
:popcorn:
 
Body weight (or body mass) is only one factor. Body volume is the 2nd one. The more displaced water (by your body, suit, equipment), the more lift from the water.

An additional 4kg to compensate higher salinity, sounds like a lot to me. Unless this person displaces a lot of water.....
 
Assuming the diver was weighed to neutral, body volume is proportional to body weight, and we do not need to include volume in the calculation.

4 kg added weight is correct if going from fresh water to the read sea, with at total weight of 100 kg and a salinity of 4% (by weight).

Red Sea - Wikipedia
 
I'm really bad at math, but for me switching from any ocean to Red Sea diving (my gear and suit being the same) is somewhere between 2 and 4 kg. I attribute the range to different tanks.
 
Hence the difference between normal sea and the Red sea should be just 1%, or between fresh water and Red Sea 3.5%. BTW I hear similar stories about the Mediterranean sea.

The OP claims that this 1% or 3.5% difference is 4kg which can't be true unless the OP dives with 400kg of lead in normal sea or 115kg in fresh water. Doesn't make sense to me...

For a "typical" 5-10kg weight belt the difference should be hardly noticeable (100-300gr or so)...

It is a bit late here and I am tired so my maths might be a bit off...
no thats not true it is1% of the divers total weight not 1% of the previous amount of lead..
 
I am pretty sure @victorzamora means 3,5 % of total weight (3,5 kg if diver is 100kg), and that this will have to be added as lead. Not 3,5 % of your total lead weight.

I certainly could've been more clear, but yes. I meant you need to add 3.5% of the total weight of the "diver system" (tank, bc, diver, lead, etc). Your "system" will displace the same amount of water, so the "system" needs 3.5% more weight to still be neutral.

So a 100kg "diver system" would need an additional 3.5kg, regardless of how much lead they wear in freshwater.
 
Suppose I displace 100,000 cubic centimeters of water, which is the most reasonable round number for a male with scuba gear. 100,000 cubic centimeters of pure water weighs 100 kg, 102.4 kg (102.5 for using the numbers on this thread) for 'normal' salt water and up to 103.5 kg for red sea water. So an extra 4kg compared to fresh water is reasonable. An extra 4kg compared to normal salt water is much harder to believe, but not out the question for a very large man with a very large amount of gear.
 
https://www.shearwater.com/products/teric/

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