ballasting for freshwater

[1 Tadpole]

OK, I need some help.

I've finally dialed in my ballast for saltwater. A whopping 18 lbs. with my Cressi Super Comp! I've yet to be deeper than 35 feet with all of it but I anticipate I'll drop pretty [damn] fast past 35 because I seem to be neutral at about 32!

There's plenty of freshwater around here and I've been tempted to dive some but I need some advice on how to calculate a ballast starting point for to work from.

Any and all help is appreciated. Thanks!

Tad

 

[Jon]

Start by taking off 10%-20%. Next, dive down and get neutral at whatever depth your comfortable at- I go for 33' if I am freediving and shallower, like 8', for freshwater spearfishing.

Jon

 

[Pezman]

I think that a good starting point is to subtract 3% of your body weight from the belt, and then tweak it up or down from there. Generally, I test out the weighting by either popping down to 30 feet and seeing if I sink or float, or alternatively by just figuring out my neutral depth.

Here's the rationale behind the "3% of body-weight" rule. If you assume that you are a constant-volume object and that you are neutrally buoyant at the surface, then you are displacing exactly your body volume of water. Since salt water is about 3% denser than fresh, you should adjust your weighting by about 3% of your body weight. Of course, you are not a constant volume object and you are probably about 6# positive at the surface and we are neglecting the effect of the weight that you already have on. Still, if you adjust those parameters a bit, plug in the numbers and note that some of the errors tweak the estimate up while others tweak it down, you'll find that the weighting usually up or down by less than 1# (unless you are super huge or super tiny). This means that when you check out your buoyancy you can probably dial it in by discarding 1# if you're too heavy or adding 1# if you're to light -- but at least you will be pretty close on that first dive.

I had the same experience as you (only reversed) when I recently went to CA and did my first ocean dives. I was surprised by how under-weighted I was, which caused me to give some thought to weighting.

Hope that helps, and others might have some slightly different thoughts on the subject (so I'll be eyeing this thread)

 

[cdavis]

Thanks Pezman and Jon.

I'll be doing some fresh water diving soon and this exact question was puzzling me.

Connor

 

[1 Tadpole]

Jon and Pezman,
Thanks for your guidance. Very helpful.

Thanks,
Tad