johndiver999
Contributor
No reread the scenario I provided, it was very explicit and was neutral (strictly for simplicity)
Displacement of Scooters at Depth - Spun off from the A&I Discussion about Nothernone
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Dan
Contributor
Agree.
I was just trying to say that the net weight in the water would be different if it is not neutrally buoyant.
If an object has 2.1 kp (positive) buoyancy with internal air volume of 11 liters. The net buoyancy will be -8.9 (-11 + 2.1) kp as the case of AL80
If an object has -3.5 kp (negative) buoyancy with internal air volume of 10 liters. The net buoyancy will be -13.5 (-19 - 3.5) kp as the case of Steel 300 bar tank.
Dan
Contributor
You did. I must have missed it. Sorry!
I was fixated on the AL80 example few pages back, which is not neutrally buoyant.
Dan
Contributor
I use kp because other use it here. Since we are talking about force, it's easier and less confusing to use kp than Newton. 1 kp = 1 kg force = 1 kg mass x gravity acceleration of 9.8 m/s2 = 9.8 Newton.
Using l for liter could be mistaken as I (capital letter of i) in my too smart iPhone spellchecker.
InTheDrink
Contributor
Omg I came here to look at scooter accidents and came away vastly more horrified by many people’s grasp of incredibly basic physics ordinarily considered a given in scuba diving.
Fwiw, I had a minor scooter incident on my first trip using a scooter a couple of years back. Naturally I hadn’t done a training course nor read the manual because yeah.
Around 40m while trying to video some hammers I suddenly felt heavy. Very heavy. I instinctively knew the scooter cavity was flooded. The motor was still working. My wing has 18kg lift.
Pointing the scooter upwards generally speaking, finning moderately and inflating my wing allowed me to ascend slowly and abort the dive.
When I got back on the boat I thought it might be interesting to looking at the DPV manual and see if there were any protocols.
1. It said that the DPV if flooded is 18kg negative. Duh, it also weighs ~18kg on land.
2. If flooded it said to ditch DPV.
I could and would have ditched the DPV if it was dragging me down aggressively or I couldn’t get it under control. In my situation it was borderline so I preferred to keep the kit.
From memory there was a little task loading from managing the DPV (trying to orientate it upwards, monitoring my depth and managing a camera rig. I would be very surprised if a competent scooter user would struggle with releasing a flooded DPV. At least one or two significant elements of task loading would have to be introduced or else a different or additional failure mode (implosion/wing without enough lift/insert any number of arbitrary stuff here)
And damn it, brush up on the physics. Not equations or calculators required unless you’re nit picking which is 100% pointless for managing the safety element here
Fwiw, I had a minor scooter incident on my first trip using a scooter a couple of years back. Naturally I hadn’t done a training course nor read the manual because yeah.
Around 40m while trying to video some hammers I suddenly felt heavy. Very heavy. I instinctively knew the scooter cavity was flooded. The motor was still working. My wing has 18kg lift.
Pointing the scooter upwards generally speaking, finning moderately and inflating my wing allowed me to ascend slowly and abort the dive.
When I got back on the boat I thought it might be interesting to looking at the DPV manual and see if there were any protocols.
1. It said that the DPV if flooded is 18kg negative. Duh, it also weighs ~18kg on land.
2. If flooded it said to ditch DPV.
I could and would have ditched the DPV if it was dragging me down aggressively or I couldn’t get it under control. In my situation it was borderline so I preferred to keep the kit.
From memory there was a little task loading from managing the DPV (trying to orientate it upwards, monitoring my depth and managing a camera rig. I would be very surprised if a competent scooter user would struggle with releasing a flooded DPV. At least one or two significant elements of task loading would have to be introduced or else a different or additional failure mode (implosion/wing without enough lift/insert any number of arbitrary stuff here)
And damn it, brush up on the physics. Not equations or calculators required unless you’re nit picking which is 100% pointless for managing the safety element here
fsardone
Solo Diver
Always challenging to work out the displacement of a bag — volume of a cylinder knowing the flat dimension…
I always carry two full size SMBs (primary and backup) and often a third small yellow one.
Knowing the cost of the scooter I’d like to think that I’d use two bags and winch it up rather than donate it to Neptune’s Locker. Reality though…
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