bill harvey
Contributor
Well dive shops seem to be able to guess pretty well how much weight you will need to wear in salt water in a given weight suit, how is it done is there a formula?
Are there charts or is there a formula to how much weight you should need to wear?
- Thread starter bill harvey
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I've never seen a table for this - there are just too many variables.
There is a formula that's really quite simple, until you attempt to implement it. You need to determine the volume and mass of the diver in order to caclulate the density, then adjust to correspond to the density of the water.
The practical application of this formula can be described thusly:
Steven
There is a formula that's really quite simple, until you attempt to implement it. You need to determine the volume and mass of the diver in order to caclulate the density, then adjust to correspond to the density of the water.
The practical application of this formula can be described thusly:
- Gear a diver up.
- Throw diver in the soup.
- Tether diver at 10ft.
- Wait until only 500 psi remains in tank.
- Remove all air from BC.
- Add weight until neutral bouyancy is achieved.
Steven
I learned this in my ITC from Dr Bob, and so far it really, really works.
First off, most shops sell a student weigh too much wayt. :tease: 10% is very high down here in sunny Florida where skins and 3 mils are the norm. I can't imagine using ten percent of my body weight to get me down. To sink a ship, yes... but way too much for me.
Do this at the pool... put on the full gear you will be wearing for your dive. Wet suit, booties, fins, and a FULL TANK TOO! This method will get you perfectly weighted for when you do that safety stop. I have used it on a ton of students with GREAT success!
1) Remove all weight. I put lots of weight by the side of the pool for this.
2) Empty your BC bladder FULLY (get that arm way into the air when you vent).
3) Cross legs and fold hands (stop swimming or sculling!!!).
4) Relax and breathe normally through your regulator.
5) When you have stabilized, have someone measure how far the top of your head is out of water. If you are already submerged, then you don't need additional weight you lucky dog!!!
6) 1"=1#, so if you are 8 inches out, grab 8 pounds and remeasure. If you are 10 or more inches out start with ten pounds. Repeat measuring and keep adding weight until just the top of your head is even with the water surface... If one more pound makes you sink remove the pound. BTW, I usually just have the student hold the weight in their hands at this point... helps to stop them sculling. You have to be relaxed!!!
7) Salt water is 3% heavier than fresh... SO, you will need an extra 3% of your entire weight (you and the gear) to sink you. Generally, we find that 4-8 pounds works for most people when going from fresh to salt (skinny=4#, fat=8#).
Hope this helps!
First off, most shops sell a student weigh too much wayt. :tease: 10% is very high down here in sunny Florida where skins and 3 mils are the norm. I can't imagine using ten percent of my body weight to get me down. To sink a ship, yes... but way too much for me.
Do this at the pool... put on the full gear you will be wearing for your dive. Wet suit, booties, fins, and a FULL TANK TOO! This method will get you perfectly weighted for when you do that safety stop. I have used it on a ton of students with GREAT success!
1) Remove all weight. I put lots of weight by the side of the pool for this.
2) Empty your BC bladder FULLY (get that arm way into the air when you vent).
3) Cross legs and fold hands (stop swimming or sculling!!!).
4) Relax and breathe normally through your regulator.
5) When you have stabilized, have someone measure how far the top of your head is out of water. If you are already submerged, then you don't need additional weight you lucky dog!!!
6) 1"=1#, so if you are 8 inches out, grab 8 pounds and remeasure. If you are 10 or more inches out start with ten pounds. Repeat measuring and keep adding weight until just the top of your head is even with the water surface... If one more pound makes you sink remove the pound. BTW, I usually just have the student hold the weight in their hands at this point... helps to stop them sculling. You have to be relaxed!!!
7) Salt water is 3% heavier than fresh... SO, you will need an extra 3% of your entire weight (you and the gear) to sink you. Generally, we find that 4-8 pounds works for most people when going from fresh to salt (skinny=4#, fat=8#).
Hope this helps!
Former FLL Now MSP Diver
Contributor
Here's the PADI Basic Weighting Guidelines. These are based on an average individual, diving in salt water.
Swim or dive skin - 1-4 lb
Thin (3mm) one piece wet suit - shortie or full - 5% of your body weight
Medium (5mm) two piece wet suit - 10% of your body weight
Thick (7mm) two piece wet suit with hood and booties - 10% of your body weight plus 3-5 lb
Neoprene dry suit - 10% of your body weight plus 7-10 lb
Shell style dry suit with non foam underwear - 10% of your body weight plus 3-5 lb
Shell style dry suit with heavy or foam underwear - 10% of your body weight plus 7-14 lb
You can convert the above from salt water to fresh water (or vice versa) using the following estimates. The weights given are either added for fresh to salt water converions, or subtracted for salt to fresh water conversion, based on your body weight.
100-125 lb - 4 lb
126-155 lb - 5 lb
156 - 186 lb - 6 lb
187 - 217 lb - 7 lb
You also need to figure in buoyancy for your tank. An aluminium 80 becomes approximately 5 lb positively buoyant by the end of a dive. You may need to add some additional weight to compensate for this beyond the above guidelines. Steel tanks may require less, if any. Also
As noted, there are a number of variables that come into play. These can be used as a starting point, and you can add or subtract a pound here or there as you practice and get more experience. As always, YMMV. Hope this helps.
Marc
Swim or dive skin - 1-4 lb
Thin (3mm) one piece wet suit - shortie or full - 5% of your body weight
Medium (5mm) two piece wet suit - 10% of your body weight
Thick (7mm) two piece wet suit with hood and booties - 10% of your body weight plus 3-5 lb
Neoprene dry suit - 10% of your body weight plus 7-10 lb
Shell style dry suit with non foam underwear - 10% of your body weight plus 3-5 lb
Shell style dry suit with heavy or foam underwear - 10% of your body weight plus 7-14 lb
You can convert the above from salt water to fresh water (or vice versa) using the following estimates. The weights given are either added for fresh to salt water converions, or subtracted for salt to fresh water conversion, based on your body weight.
100-125 lb - 4 lb
126-155 lb - 5 lb
156 - 186 lb - 6 lb
187 - 217 lb - 7 lb
You also need to figure in buoyancy for your tank. An aluminium 80 becomes approximately 5 lb positively buoyant by the end of a dive. You may need to add some additional weight to compensate for this beyond the above guidelines. Steel tanks may require less, if any. Also
As noted, there are a number of variables that come into play. These can be used as a starting point, and you can add or subtract a pound here or there as you practice and get more experience. As always, YMMV. Hope this helps.
Marc
OP
bill harvey
Contributor
well this is fun all i really need to know is if i will have enough weight with me or if i should get more i will be diving a single al80, 7mm foam neoprene drysuit in the salt water,i weight in at a feathery 130ish pounds, i ownly own 32 lbs of weight will i need more i hope not.
You will absolutely *not* need 32 pounds of weight. I'd suggest you find a pool, get a tank down to about 500 psi, then find just how much weight you need to sink with an empty bladder. I'll bet it'll be under 20 pounds.
Not in my pool, you don't!
Rick
I have corected it to read BC bladder...
Well, there's a chart in my logbook... and a formula.
On the chart is the buoyancy, positive or negative, of every piece of dive gear I own, including my body. Tanks are tested with 500 psi remaining.
So, when I get ready to dive, using the table in my logbook for the information, I algebraically add up all the positive and negative buoyancies of me and all the stuff I'm wearing and I find out precisely how much weight I'll need (if any) to be neutrally buoyant at the surface with 500 psi in the tank(s) I'm carrying - in fresh water.
The formula is the salt water conversion factor - which is 2½ pounds additional weight required for every 100 pounds total weight of me and my stuff - typically 6 - 8 pounds for me.
By knowing the buoyancy of each item of dive gear, of my body and by knowing the salt water conversion factor, I am always assured of proper weighting every time. No guessing.
Rick
I was taught the 500 psi method... but I had to wait till the end to get it right. Honest injun, the full tank method really, really works. It just puts the water line at the top of your head and not in the middle of your mask. Best thing, is that it can be done at the VERY BEGINNING of your dive!
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