Weights?

whats the mathmaitcal equation to figure out how many weights you should have?

There really isn't one. There are simply too many variables (what you are wearing, your build, the amount of body fat you have on you, etc. etc. etc.) The PADI open water manual has a section on this and gives you some general guidelines to use as a starting point. I would imagine that the other rating agencies provide similar advice.

Regards,
<TED>

goldfish05:

whats the mathmaitcal equation to figure out how many weights you should have?

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The Archimede's law

You need to know your total volume (the ammount of water that your body and your equipment displaces) and your total weight. Then, you'll need enough lead weights to compensate for the fact that you have less weight that the ammount of water you are displacing.

In practice, you need to enter the water with full equipment (but with the empty tank), and the BC fully deflated. Then, you add or remove lead until you float at eye level with full lungs, and start to sink when you exhale. If you use a very thick wetsuit (that will compress a lot), then you can even drop a little more weight, because your target would be to be neutral at the safety stop with the empty tank, not at surface (the wetsuit is compressed at a depth of 5m already, so you'll total volume decreases).

You do this with the empty tank because the full tank weights ~1.2 kg per each cubic meter of air inside (so a full 15L tank will be ~3.6 kg heavier than when empty). Because of this, you start the dive a little heavier, and progress towards neutral while you use the air.

goldfish05:

whats the mathmaitcal equation to figure out how many weights you should have?

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W_c = Pb_n x L_bs

Where W_c = weight check, Pb_n = the the number of weights you need, and L_bs the number of pounds each weight weighs.

ok thanks for the help everyone.

Also keep in mind that the weighting result is valid for a specific set of scuba equipment. If you use different equipment pieces, you need to recheck. This is specially true for parts of equipment with significant buoyancy characteristics (exposure protection suit and the tank are the most important here). Your weighting for a 15L steel tank will be different than the one for a 10L Al tank. Also, the salinity (or lack of) of the water will change the weighting a lot.

For example, with my equipment and a 15L steel tank in the Black Sea I required 8kg of lead. With the same equipment, but a 12L Al tank in the Red Sea (change of tank and salinity) I needed 14kg of lead.

As someone mentioned, PADI has a guideline in the manual. Hope this helps.

Below is a copy of those guidelines:



These guidelines assume an average build individual in salt water. Decrease the weight somewhat for lean individuals and increase it for heavier individuals
Exposure Suit TypeStart WithSwimsuit/dive skin1 - 4 lbs3 mm/1/16 in. one piece wet suit, shorties, jump suit5% of your body weight5 mm/3/16 in. two piece wet suit10% of your body weight7 mm/1/4 in. wet suit w/hood & gloves10% of your body weight, + 3 - 5 lbsNeoprene dry suit10% of your body weight, + 7 - 10 lbsShell dry suit, light undergarment10% of your body weight, + 3 - 5 lbs Shell dry suit, heavy undergarment10% of your body weight, + 7-14 lbsSalt/Fresh Water changeBody WeightAdd(going to salt) or subtract (going to fresh)100 - 125 lbs4 lbs126 - 155 lbs5 lbs156 - 186 lbs6 lbs187 - 217 lbs7 lbs

The equation for correct weighting is:

1 diver + type of water they are going to dive in + no air in BC + normal gear + tank at around 30-50bar + correct weight = floating at eye level

DiverDean59:

As someone mentioned, PADI has a guideline in the manual. Hope this helps.

Below is a copy of those guidelines:



These guidelines assume an average build individual in salt water. Decrease the weight somewhat for lean individuals and increase it for heavier individuals
Exposure Suit TypeStart WithSwimsuit/dive skin1 - 4 lbs3 mm/1/16 in. one piece wet suit, shorties, jump suit5% of your body weight5 mm/3/16 in. two piece wet suit10% of your body weight7 mm/1/4 in. wet suit w/hood & gloves10% of your body weight, + 3 - 5 lbsNeoprene dry suit10% of your body weight, + 7 - 10 lbsShell dry suit, light undergarment10% of your body weight, + 3 - 5 lbs Shell dry suit, heavy undergarment10% of your body weight, + 7-14 lbsSalt/Fresh Water changeBody WeightAdd(going to salt) or subtract (going to fresh)100 - 125 lbs4 lbs126 - 155 lbs5 lbs156 - 186 lbs6 lbs187 - 217 lbs7 lbs

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I noticed the format isn't very good. Try the attached excel spreadsheet.

Generally, you can start out with 10% of your body weight and, depending on your percentage of body fat, take off or add on from there. With myself at 180 pounds and my body fat ratio, in salt water wearing a 2mm shorty and a BCD, I need 16 pounds of lead to sink. Wearing a full 3mm suit it takes 18 pounds. A younger, leaner person would needs less I figure.