How much ditchable weight is best?

[Daryl Morse]

Normally you are. If you dor Rock Bottom planning you will never ascent with a near empty tank under normal conditions

I don't do rock bottom planning but I never ascend with a near empty tank either. That said, if under some "abnormal conditions" I had to ascend with a near empty tank (e.g., having had to share air with my buddy), the last thing I'd want would be to get floaty at 10 or 15 fsw, which would be the case if I was normally neutral at 20 fsw with 1/3 of a tank. In fact, if you plan to be neutral at 20 fsw with 1/3 of a tank, that excerbates the problem closer to the surface with less air in the tank. I don't understand why you would advocate such weighting.

 

[jonnythan]

You must be seriously over weighted, i wear a full 3mm, alum plate, 2 lb of weights and are still neutral with an empty alum 80 at the surface

This may come as a surprise to you, but different people have different buoyancy characteristics

I sink in a pool with no lead, but I know one other fairly lean person who happens to have giant lung volume and needs several pounds to be able to sink.

Personally, with an Al 80, I'm perfect with just a steel plate, and that's in fresh water. This makes perfect sense, since I'd need -4 just to offset the empty tank, plus another pound or two to sink me+suit, which is positive at the surface.

I have no doubt that in salt water I'd need a couple more.

 

[Albion]

This may come as a surprise to you, but different people have different buoyancy characteristics .

Yes i realise that, i met a guy once (who ok, did not have an ounce of fat on him) who dove with a transpac full 3mm and still no weight with an Al80.

I have seen many people diving single Al80 with SS backplates, full 3mm and ZERO extra weight, and all admit they were still a bit negative. 3mm shorty ss plate and still need weight im suprised, no amazed

 

[Reinoud]

I don't do rock bottom planning but I never ascend with a near empty tank either. That said, if under some "abnormal conditions" I had to ascend with a near empty tank (e.g., having had to share air with my buddy), the last thing I'd want would be to get floaty at 10 or 15 fsw, which would be the case if I was normally neutral at 20 fsw with 1/3 of a tank. In fact, if you plan to be neutral at 20 fsw with 1/3 of a tank, that excerbates the problem closer to the surface with less air in the tank. I don't understand why you would advocate such weighting.

The way I learned it during my fundamentals was to weigh myself with a near emtpy tank (30 bar) on a depth of 3 metres. That is a situation you normally will only experience in the worst-case scenario. And it means that you can still do the last deco stop.

 

[SDAnderson]

I'm switching to a BPW. Of course this means I will lose a significant amount of ditchable weight if I get a SS plate. In the tropics I might be diving with as little as 4-6lbs. Locally it will be more like 10-12 lbs. With an Al plate I'd clearly be carrying 8lbs at a minimum (ditchable)

I know you shouldn't dive over weighted. But I also know you shouldn't dive with too much unnecessary weight. So the big q is...how much ditchable weight is "recommended"?

Thanks.

The smaller the increment, the better. Certainly no more than 5 pound increments, though I like 2 pound increments. You want to be able to ditch just enough to be able to swim up so that you can minimize the polaris effect in shallow water.

Since when did diving with ditchable weights become "un-DIR?" In the old days there was a lot of discussion amongst the dark throng about battery cannisters being an acceptable alternative to more conventional ditchable weights - ditchable weights were a required safety measure. I missed the memo on the new policy, it would seem.

Yes, for several good reasons, a drysuit would be part of the DIR approach to his diving. That doesn't obviate ditchable weight, however.

 

[Daryl Morse]

The way I learned it during my fundamentals was to weigh myself with a near emtpy tank (30 bar) on a depth of 3 metres. That is a situation you normally will only experience in the worst-case scenario. And it means that you can still do the last deco stop.

I thought the idea of rock bottom was to cover a worst-case scenario. (Don't get me wrong, I haven't been trained on the application of rock-bottom planning.) If you subscribe to the use of rock-bottom planning, I'd think you'd want to cover worst-case scenario in your weighting as well.

For me, I like to control my ascent, even going through 10 fsw to the surface. I don't like being a passenger. In your scenario (neutral at 20 fsw), if I understand you correctly, you would be a passenger once you began your ascent to the surface with less than expected air in the tank.

Oh well, to each, his own. Let's agree to disagree.

 

[mweitz]

Daryl,

He is weighting himself so that if he doesn't have any air, he can still control his ascent to the surface at any depth. By doing your weight check at 3M (or 9') on a near empty tank, you are doing this. Does that make sense? I think you are both saying the same thing.

Mark