First wingless (pool) dive

[aquaregia]

I was in the pool today sorting out my weight for the twinset and thought "what the hell", so I took my AL plate off the tanks, slapped on some cambands and an 80 and hopped in. I messed around for a while and took the tank from 3000 to 1200, and settled on 6# for the pool-depths (7mm, ALBP). I couldn't stay motionless at <5' with the tank pressure at 1500 or less, but 5-14' wasn't a problem. With 2000psi I was able to hold 4' even.

I'm planning to take this to the Breakwater and do a 15-20' dive along the wall. I'll have one of my standard buddies with standard gear, and I'll take my 40# DSMB as a contingency. I'm thinking that 5-6# or so should be right, accounting for fresh->salt and the slight depth difference, but this sort of sounds like a small amount of weight. With my BP/W I've been using about 14# total weight, and this would only be about 8#. I'm also thinking I should use an LP72 and take another 3-4# off my belt, but somehow SCUBA+7mm+3# weight belt just seems a little strange. Does anyone have any feedback about my diveplan or weighting?

I'd like to acknowledge all the people who've offered to take me BC-less diving, and I'm sad that I haven't found time to take anyone up on it. Thanks for any replies.

 

[Lenaxia]

In terms of weighting, the fresh to salt ratio is 1:1.03, the way I do my weight conversion between the two is to:

1) take my dry weight with all my gear, sans weight.
2) jump in the pool and pick up enough weight to get me neutral with no air in my wing.
3) Add the dry weight with the weight to get neutral. This will give you your total buoyant force in a fresh water body of water.
4) multiply by 1.03 then subtract your dry weight and that will give you the weight you should need on your belt.

It should be noted though, that chances are it will overestimate your weight by 2-3 lbs as a pool is not fresh water, it is chlorinated water which obviously is more dense than fresh water. If you have the tools you can calculate the density of the pool water but I doubt its worth the effort considering everything.

BC-less diving definitely sounds fun.

 

[aquaregia]

I guess to be a bit more rigorous, I should have ditched some more weight and plotted a buoyancy curve for my wetsuit. It sort of feels (based on the buoyancy changes of my tank emptying) that I should take off a pound for every 2-3 feet; hopefully someone will have some advice here. I've got 1# weights, so I was figuring I'd just fill up my buddy's pockets with a selection and let her BC hold them

 

[duckbill]

You'd be surprised how many of those pounds you were able to take off which you had to wear before just to compensate for air pockets trapped in your wings, even when "empty".

Your numbers do seem light to me, but you won't know until you try it for yourself. If you weight a bit heavy you can hand some weights to your airbag buddy until you are just right. If you weight a bit light, you'll be fighting it and burning up a lot of air if you don't grab a rock. Remember, you want to be neutral when your tank goes to reserve, not at the beginning of your dive. But, neutral at what depth? Different people will give different answers. Some say you should be neutral at depth, and some say at 10 feet or so. Your call. You definitely want to be buoyant at the surface at the end of your dive for any surface swim you may need to make.

 

[captain]

Wearing that much rubber your buoyancy will be different at the end of the dive compared to the beginning. It take a while and some depth to get all the air out of a wet suit plus they don't regain as much at the end of the dive as they loose at the beginning. Although a wet suit is made of closed cells some percentage get ruptured over time and use. The pressure squeezes the air out of the ruptured cells on the way down and water is sucked into the ruptured cells on the way up causing a loss of buoyancy.
Another thing is it helps to get out of the safety stop neutral buoyancy at the end of the dive thing. In the heyday of no BC diving there was no such thing as a safety stop. Properly weighted for a no BC dive means you will be a little buoyant at the end.

 

[Eric Sedletzky]

Dude,

Anytime you want to go out and practice no BC diving you let me know. I will make a special point to make sure we get out there and get you dialed in. You're close enough we can make this happen either at Breakwater or up here at Gerstle or Stillwater (on a decent day).

It's really not hard with the weighting. The easiest way to figure it out is to do some freediving in the wetsuit, fins, etc you will be using with your scuba and set your weight so you can break neutral at about 20 feet.
From there subtract off your weightbelt whatever you add onto your back in terms of plate, tank, stainless cam buckles, reg (if it's a heavy one) all that stuff adds up. It just takes a few trial dives and a few trips back and forth to the beach and you'll get it.
I have plenty of 72's to use, as a matter of fact I have some for sale with fresh hydros if you want one, cheap!
I can even show you how to rig up a tank to wear with no plate at all if you really want to be minimal.
The weighting is all in the trade off between the rig and the belt.
The key is to be able to float on the surface with a full tank and then fight your way down head first (just like freediving) and break neutral at 15 or 20 feet.

Another thing, as air gets used up you will lose weight in the tank but at the same time your wetsuit will compress and cool down which both combined will minimize the getting light thing at the end of the dive. So instead of the swing being 5 or 6 lbs. it might only be 2 or 3 lbs. and that's easy enough to overcome with breathing. I'm light enough that I have to start looking for rocks to carry around at 15 feet towards the end of my dive.
Hanging onto kelp is another way. Hey man, in California we use what we have available right?

If you really really want to get minimal I can set you up with a J valve/ rod and you can see what it's like to time your dive and pull the J instead of constantly looking at an SPG.

 

[aquaregia]

I'd love to take you up on that. I've been hoping to get up to the North Coast for a while, but I haven't been able to get it in the schedule.

What's the advantage in a plate/backpack over just a simple harness?

 

[Eric Sedletzky]

I'd love to take you up on that. I've been hoping to get up to the North Coast for a while, but I haven't been able to get it in the schedule.

Let's keep an eye on the December NCD dive. Some of those guys are going down to the Peace later in the month and considering that the December club dive, but there's no reason why we can't set up some sort of dive up here.

What's the advantage in a plate/backpack over just a simple harness?

Stability, added weight (if it's stainless), comfort (although in a thick wetsuit there's enough padding that a straight tank is no big deal). It also allows the tank to be dropped far enough down to balance out trim (if needed).
There's also one other factor that doesn't really affect modern reg divers, but for people who use a double hose, using a plate or backpack allows the tank to be dropped far enough down that the can of the reg can sit low and close in enough to the center of the lungs to really make them work nice.
By just strapping up a tank, the highest the harness can be set is right at the shoulder of the tank which when the straps go over the shoulders (of the diver) brings the tank higher than using a plate, but still lower than todays BC standards and certainly still managable.
With a plate the top cam band determines how low the tank can go and the shoulder straps come out of the plate much higher than that the top cam band around the tank, so this enables the diver to really wear the tank low if they want to. You have to remember, there is no BC to carry around the tank. It's now depends on your suit, your lungs, and where you place the tank. You ride the tank too high like you can with a wing and you'll end up on your head.

Look over at my avatar and you can see that I have the top cam band right at the shoulder of the tank. Now look at where the shoulder straps come out of the plate and notice that it's about five inches higher than the top cam band. If the shoulder straps came out right where the top cam band is on a straight tank strap set up, the tank would be about four inches higher.

 

[aquaregia]

That'd be great, especially if it was the first weekend in December. I'm busy on the weekends of the 11th and 18th, and I think my mother might take issue with me ditching her on the 25th

 

[simonbeans]

None, if you are trying to be authentic to the period of double hose or no BC diving. Nothing is simpler nor easier to use than a simple harness. And the price is far less than a stainless steel plate, which of course never existed in the "vintage" period.