Displacement of Scooters at Depth - Spun off from the A&I Discussion about Nothernone

[Dan]

There's a difference between a scooter flooding, and imploding. A significant difference.

I guess the significant difference would be time. The DPV would not suddenly act as an anchor when it starts to flood as oppose to implode. He would have time to assess & response accordingly. The margin of error, in terms of CO2 retention that would lead to loss of consciousness from over exertion is much greater in 150’ than in 700’. Implosion would be less likely to happen at shallower depth.

What would happen if the flooding led to the salt water shortcircuiting the battery? Would an explosion be possible?

 

[Akimbo]

I guess the significant difference would be time.

I would say that the implosion shock wave is a more critical factor than time. A moderate-size camera housing implosion can take fingers off and knock you silly. Implosion shock waves dramatically increase with the pressure vessel volume. Scooters aren't certified to the same standards as a deep submersible or military submarine. Welds don't get X-Rayed, metals aren't sourced with mill certifications, welders aren't certified, etc, etc.

The risk is LOW, but stress and corrosion fatigue or manufacturing flaws could result in a catastrophic housing implosion at 1/4 of the design depth.

 

[michael-fisch]

Sorry can't agree that you have much time with a flooding scooter at depth.
Almost 20 years ago I flooded the battery compartment of a 33Ah Gavin scooter at a depth of 54M. It took 4-5 seconds to flood competely and thats only with the water coming in a pressure of 5.4 Bar.
In the Font Estramar accident the pressure difference was over 21 Bar, in all likelyhood the scooter went from perfectly balanced to fully flooded in way less than 2 seconds. If the tube split (implosion) the hydrostatic shock would have been enough to incapacitate the diver for a period of time.
Batteries in good scooters are traditionally floodproof since a 45V 50Amp battery pack that shorts out over 0.1 seconds will give off approx 81 Megawatts. Got no idea how much energy 4oz of TNT can develop, but it can't be much less.
I have unfortunatly welded a wrench when I fumbled it onto one of my 26V 51Ah LiFePO4 scooter packs, what saved the day was that the 25 sqmm busstraps selfdestructed before major damage was done.
Michael

 

[boulderjohn]

Scooters and Buoyancy
In the water, it is not the weight of an object that counts, it is the buoyancy, which is determined by a combination of weight and volume. If a scooter weighs 40 pounds on the surface, it will still be neutral at depth because the weight of its total volume will equal the weight of the water it displaces. If it floods, it does not suddenly become 40 pounds negative, because it maintains its volume. It becomes negative by the added weight of the water that displaces the volume of air within the scooter. Most of the interior of the scooter is motor and battery, and the weight of the motor and battery does not change.

A huge difference between implosion and flooding is not just the force of the implosion. If a scooter implodes, it will lose volume, which will make it much more negative than a scooter that has flooded but maintained its volume.

 

[Dominik_E]

Scooters and Buoyancy


A huge difference between implosion and flooding is not just the force of the implosion. If a scooter implodes, it will lose volume, which will make it much more negative than a scooter that has flooded but maintained its volume.

If a completely flooded scooter somehow managed to implode actually not. A water filled volume is neutral in water. The only thing that will in theory change is the drag when the scooter gets compressed. Probably not a huge factor. In reality incomplete flooding is however a necessary precondition for an implosion to even happen: water and solid materials are incompressible.Thus, if the scooter imploded, it can not have been completely flooded beforehand, so yes, it will instantly loose buoyancy. Not because of change of shape, but because of loss of air filled spaces...

 

[Dan]

A huge difference between implosion and flooding is not just the force of the implosion. If a scooter implodes, it will lose volume, which will make it much more negative than a scooter that has flooded but maintained its volume.

I think the negative buoyancy of imploded scooter and fully flooded scooter would be the same because the difference in volume are occupied by the same density of water, plain physics.

 

[Jiminy]

Scooters and Buoyancy
In the water, it is not the weight of an object that counts, it is the buoyancy, which is determined by a combination of weight and volume. If a scooter weighs 40 pounds on the surface, it will still be neutral at depth because the weight of its total volume will equal the weight of the water it displaces. If it floods, it does not suddenly become 40 pounds negative, because it maintains its volume. It becomes negative by the added weight of the water that displaces the volume of air within the scooter. Most of the interior of the scooter is motor and battery, and the weight of the motor and battery does not change.

A huge difference between implosion and flooding is not just the force of the implosion. If a scooter implodes, it will lose volume, which will make it much more negative than a scooter that has flooded but maintained its volume.

While reading the french story someone mentioned a Cuba 650. I took a look at the user manual it said this

Flooding
If the scooter floods on the dive, it may become significantly negative and become a risk to the user. The best option is to unclip the X-Scooter via the tow cord bolt snap and release it. This will eliminate the risk and you can safely exit.

What does significantly negative mean? Thats anyone's guess that scooter is 54llbs

 

[KevinNM]

While I’m also in complete agreement with both @Colliam7 and @lv2dive and have my own experiences with a scooter to compliment their point of view. I’m also reminded of the Tech diver in a deep cave in Europe last year who for whatever reason didn’t/couldn’t disengage his scooter and followed it down past its crush depth (+ 200m) to his death

Not that I’m for one minute suggesting this is the case in this instance but we should remember the lessons of others that it can happen

There actually have been several similar accidents in that cave that involve imploded scooters. All really, really deep. I have no idea as to your mental acuity at 200+ meters, how they had it connected or how how fast you'd sink or what the autopsy determined cause of death was for diver they recovered.

It sounds like in this case he'd have been a lot shallower, with a large ledge or something to stop at short of the abyss.

 

[boulderjohn]

I don't know the air volume of the scooter he used, but I can make a comparison to a scuba tank, which has an internal volume that is 100% air. I am looking at a chart as I write and rounding everything off for ease of understanding.

The scuba tank weighs roughly 35 pounds on shore when empty.
When empty, it is neutrally buoyant, meaning it has no apparent weight in water.
It's physical capacity is 11 liters.
A liter weighs about the same as a kilogram of water.
11 kilograms of water = 24 pounds.

If filled with water, this scuba tank would weigh about 24 pounds in water as opposed to 35 pounds on land.

 

[Charles2]

A huge difference between implosion and flooding is not just the force of the implosion. If a scooter implodes, it will lose volume, which will make it much more negative than a scooter that has flooded but maintained its volume...………..

.............If filled with water, this scuba tank would weigh about 24 pounds in water as opposed to 35 pounds on land.

How much would it weigh if it imploded?