DwainT:
Tobin,
So your saying that a diver should not take into consideration stage bottles when diving... since they can be ditched. So I guess I and many others have been diving for many years with to much lift. I do not think that a diver should consider ditching tanks except in emergecy situation.... it called planning. I plan to bring my tanks back on every dive. Not be over weighted with to small of a wing.
When have I suggested that a diver ditch his stage bottle
except in an emergency?
DwainT:
Stage bottles do effect buoyancy... and the more stages the more it effects.
I never said that stages won't effect your buoyancy, what I said was stages should not be considered part of the divers weighting, and does not impact wing sizing.
DwainT:
Tobin.... Why don't you do this if you think that stage bottle to not effect buoyancy.... with your back gas use a wing that provides just enough lift to keep your head out of the water (chin level).
When have I suggested that a diver should select a wing that is only capable of keeping his chin out of the water with full back gas?
Let me run an example, using doubles and a deco bottle.
Our diver will be using the following gear:
Double E8-130, SS back plate and Harness, Dry suit with 22 lbs of initial Buoyancy,
Al 80 Stage or deco bottle. Assumes air or Nitrox for Back gas.
Weight of empty tanks = ~-2 lbs
Weight of back gas = ~-21 lbs
SS Back plate and harness = ~-6 lbs
Tank Bands and center section of Manifold = ~-5
Dual Regs = ~-5
Can Light = ~-2
Total negative buoyancy of rig with full Backgas = ~-41 lbs, or ~-20 with empty bottles.
Drysuit and undies, on the diver with minimum gas in the suit requires 22 lbs to get neutral at the surface. If this suit suffers a total failure, i.e. unable to trap gas, it could loose no more than 22 lbs of buoyancy.
Our diver needs to start this dive negative by the weight of his back gas, or -21 lbs. This will allow him to breath his back gas all the way down if he should need to in an emergency.
He needs a total of 43 lbs of ballast, 22 lbs to get his suit neutral, and 21 more so he is negative by the weight of his gas.
To stay at the surface with full backgas he will need to use 21 lbs of wing capacity, and he needs at a minimum another 22 lbs of wing capacity to offset the effects of a drysuit failure. That means he needs at a minimum 43 lbs of wing lift.
43 lbs of lift will also float his rig at the surface with full backgas 43 (max lift) > 41 (max rig negative buoyancy)
Now lets consider the effects of adding a deco bottle. Lets assume our diver actually found a 43 lbs lift wing and is happily floating at the surface using 21 of the 43 lbs of lift available to him. How much additional wing capacity does he have available? 43-21=22lbs. What is the buoyancy of a full rigged AL80? About -4 lbs, 2 lbs for the full 80 and about 2 lbs for the reg.
If our diver has another 22 lbs of capacity, and needs only to use 4 of it for a full 80 why would he need a larger wing? Even 2 or 3 al 80's won't exceed the lift available to him. If he aborts his dive 15 minutes in he's still fine with all his tanks full.
This of course on an example, in practice the diver will seldom find a wing with the exact minimum lift he needs, and will select the next size up, in the DSS line he's likely use a 49 lbs wing.
What emergency would force or diver to drop bottles? Drysuit failure, or wing failure.
If the diver's Drysuit fails and he looses 22 lbs of buoyancy he will need to drop the bottles. If his wing fails he will likely need to drop the bottles
DwainT:
Then add a single stage, then a second, an O2 Bottle and then maybe a third stage. Then go for a dive... 15 minutes into the dive abort.... then try to stay on the surface with your head out of the water. Now is there any real reason to ditch if there was proper bouyancy?
While your premise is entirely wrong, I'll also point out that the OP in this thread is diving with a single tank. How many stage and or deco bottles do you think he will be carrying?
Lets take a look at a typical single tank diver here in So Cal. We know the OP in this thread is at least tall, as he is considering a DSS Long Pattern Plate.
I'll assume or diver is using:
SS Long Pattern Plate
E8-130
Can Light
7mm full suit, initial buoyancy of 25 lbs (big guy, big suit)
His rig will have a maximum negative buoyancy of about -23 lbs with a full tank, SS Long Pattern Plate an harness is about -8, full bottle is about -11, Reg-2, can light -2.
His rig will be -~13 with an empty tank. He will need about 25 (suit buoyancy) - 13 (rig with empty tank) = 12 lbs on a weight belt
I have assumed his suit to be 25 lbs positive at the surface. If his suit is 25 positive at the surface it cannot loose more than 25 lbs of buoyancy as he descends.
I will assume that our diver will start the dive negative by about 5 lbs. That means he is Eyelevel at the surface with a full tank and only 5 lbs worth of gas in his wing. He needs enough additional capacity to compensate for a fully compressed suit, or 25 lbs.
If he's used 5 lbs of lift to stay at the surface, and needs 25 more then the minimum wing would be 5 + 25 or 30 lbs. A 30 lbs wing will easily float his rig with a full bottle 30 > 23.
How will our diver hold his shallow stop if he breathes down 8-9 lbs of gas and only started 5 lbs negative? Simple his 25 lbs positive wetsuit has lost substantial buoyancy at 15 ft. With thick neo suits and smaller tanks our diver maybe able to start the dive neutral at the surface.
Again if our diver needs only to use 5 lbs of lift from a 30 lbs lift wing why would the addition of a ditchable stage bottle require a larger wing?
If our diver is starting the dive negative by 5 lbs with a full tank, he has 25 lbs of wing lift available for "comfort" at the surface. That's a long way from "barely able to keep his chin out of the water"
What circumstances would require a 45 lbs wing for singles? Our subject diver would need to have an exposure suit that was 40 lbs buoyant. I don't know of any 40 lbs positive exposure suits being using in SoCal.
DwainT:
BTW: You should reread what was on the link... not every one breaths there tanks dry or almost dry (this causes regulators to be rebuilt prematurely from water intrusion due to pressure differential when a tank has been breathed down to empty then there is the possiblity of water in the tank)... the information relies on the tank being empty or almost empty to provide buoyancy at the end of the dive and complete reliance on your back gas as your reserve.
No it does not. An AL 80, or AL 40 will become positive well before it's empty, or the reg is in any danger of water intrusion. Where have I suggested that the diver rely on empty bottles for buoyancy?
Tobin