Weight belt equation

[Tamas]

So what is the formula or method to calculate the required weight one needs diving from a 14mm suit to a 5.6mm suit?

In other words, let's say I need 20lbs to dive in cold fresh water with a 14mm (two piece farmer john + jacket) and want to change the wetsuit to a 5/6mm 1 piece - what would be quickest way to see how much I need off the belt to accommodate the change without actually sitting in the water playing with the belt?

 

[Tamas]

anyone?

 

[O2BBubbleFree]

Back when I started the LDS provided the following charts as starting points. This is more info than you asked for, but I thought it might help you (and possibly others). Of course, a bouyancy check must then be done. # = US pounds.

In saltwater

Swimsuit or dive skin: 1-4#
1/16" (3mm) one-piece or shorty: 5% of bodyweight
3/16" (4.5mm) 2-piece (john and jacket): 10% of bodyweight
1/4" (6mm) 2-piece w/ hood, gloves, boots: 10% + 3-5#
Neoprene drysuit: 10% + 7-10#
Shell dry suit: 10% + 7-14#

For fresh water, subtract weight according the following:

If you weigh between 100 and 125#, subtract 4# of lead
If you weigh between 126 and 155#, subtract 5# of lead
If you weigh between 156 and 186#, subtract 6# of lead
If you weigh between 187 and 217#, subtract 7# of lead

This is just a rough generalization, but hope it helps.

 

[Tamas]

Thanks that is what I was looking for!

 

[Mako Mark]

there is no formula....

You need to jump in the water and adjust you weight until you either:

Float at eye level whith a normal full breath in your lungs.

or you have to exhale to descend, and when you inhale deeply, you stop descending and start ascending.

If you are using aluminium tanks, remember that they float at when empty and sink when full, so take that into account when doing bouyancy checks with full tanks.

 

[O2BBubbleFree]

there is no formula....

You need to jump in the water and adjust you weight until you either:

Float at eye level whith a normal full breath in your lungs.

or you have to exhale to descend, and when you inhale deeply, you stop descending and start ascending.

If you are using aluminium tanks, remember that they float at when empty and sink when full, so take that into account when doing bouyancy checks with full tanks.

Yes, there is a formula, or at least guidlines (see above), and there's nothing wrong with using 'em as a starting point. Nobody's saying that you don't need a bouancy check, but it's nice to know how much weight to 'jump in the water' with, then adjust from there.

Here's another formula for you: The AL80 will become approximately 5# positive at the end of a dive. This approximation will enable you to 'take that into account,' as suggested by Cancun Mark.

And another: (or at least a consideration) Diving at altitude requires more weight. Unfortunately I don't have a formula for this one. Does anyone else?

All these formulas should be taken with a grain of salt. For instance, lean people normally require less weight. However I have more than 20% body fat and am negatively bouyant. I guess I'm a natural diver; extra insulation and negative!

Anyway, Aqua Ho, glad I could help.

 

[Mako Mark]

Diving at altitude requires more weight. .

Are you sure?

Doesnt diving at altitude need less wheight as the water is fresh, therefore less bouyany?

 

[Bob3]

My "guess" was start at 6 lbs, but as already mentioned you will need to get into the water for a tryout if you don't want to run the risk of stuffing rocks in your suit or commit the sin of overweighting and wind up using your BC as a weightbelt compensating device.

 

[Groundhog246]

Are you sure?

Doesn't diving at altitude need less weight as the water is fresh, therefore less bouyany?

Don't see why altitude would have anything to do with the weight required. It affects surface air pressure, but the density of water stays the same. Fresh water IS less dense and requires less weight, but you can have salt water lakes at altitude (there's not many, but they exist).

 

[O2BBubbleFree]

Don't see why altitude would have anything to do with the weight required. It affects surface air pressure, but the density of water stays the same. Fresh water IS less dense and requires less weight, but you can have salt water lakes at altitude (there's not many, but they exist).

Just 'cause you can't see it, doesn't mean it's not there. Surface air pressure does affect water density, but more on that later...

WRT the subject of the thread, surface air pressure affects your wet suit. The air pockets in closed-cell neoprene expand with altitude, and it takes more lead to sink it. When I was living in Sacramento CA I had an equal number of dives in Monterey and Lake Tahoe, and used 24# at each location. The loss of buoyancy from salt to fresh was offset by the increased buoyancy of diving at that particular altitude.

On a side note, given the above replies, I feel I need to address diving at altitude in general. Surface air pressure affects water density in that the weight of the air pressing down on the water is much less at high altitudes. In my physics classes I was taught that the density of pure water can be taken as a constant only at sea level.

If there is anyone out there considering diving at altitude (more than 1000' above sea level) I strongly suggest getting the specialty certification (from an instructor that knows his stuff) or doing your homework. Lead is the least in a long line of considerations. The NDL tables are different at altitude, safety stop depths and times are different, normal gauges will not be accurate,. and if you have been 'at altitude' for less than 24 hours there are additional considerations (your first dive must be planned as a repetitive dive and you must account for any mountain passes that you drove over)...