SS at 10ft or 20ft -- Why not standard 15ft?

[Wibble]

You are more streamlined in a horizontal position if your swimming - if you are doing a SS or deco stop - and therefore not swimming- a horizontal position creates far more resistance to rising and descending than a vertical position would.

And suit squeeze in the legs whilst the gas bubbles out of the dump.

And flapping feet kick people below you

 

[Hojo in SC]

Are there computers that actually do this? I’ve had 2 lower end computers and both have a good margin, so I’m curious as to which ones don’t.

From the Shearwater Peregrine:

"Automatic Countdown
Countdown begins once the depth becomes shallower than 6m (20ft ). Countdown will continue while the depth remains in the range of 2.4m to 8.3m (7ft to 27ft).
Countdown Paused
If the depth goes outside of the range 2.4m to 8.3m (7ft to 27ft), then the countdown pauses, and the remaining time displays in yellow."

I know my Wisdom 3 will stop as well, just not sure of the exact depth.

 

[RIHappyDiver]

From the Shearwater Peregrine:

"Automatic Countdown
Countdown begins once the depth becomes shallower than 6m (20ft ). Countdown will continue while the depth remains in the range of 2.4m to 8.3m (7ft to 27ft).
Countdown Paused
If the depth goes outside of the range 2.4m to 8.3m (7ft to 27ft), then the countdown pauses, and the remaining time displays in yellow."

I know my Wisdom 3 will stop as well, just not sure of the exact depth.

Sorry, I think you misunderstood my question. I was responding to you stating that a computer might start your safety stop countdown over again if you don’t stay at exactly 15ft. Both of the computers I have used will do what you describe above, though not with as large of a range, but I have never heard of a computer that needs you to stay at exactly 15ft in order to finish a SS.

Erik

 

[boulderjohn]

Do your SS at 20 feet. It’s the Maximum Operating Depth (MOD) for 100 % Oxygen. I understand that isn’t how your diving at this point in your scuba training but it is good practice for to start to think and act that way.

I am lost on the benefit of doing this.

 

[boulderjohn]

Setting it at 20 and bumping to 15 verses setting at 10 and never getting there theoretically maybe gets you out quicker than your initial TTS, not later - just one of those stupid detail things.

Why?

 

[ChuckP]

Why?

For no reason other than boredom

 

[lowwall]

You are more streamlined in a horizontal position if your swimming - if you are doing a SS or deco stop - and therefore not swimming- a horizontal position creates far more resistance to rising and descending than a vertical position would.

Ahh, now I see your point. You are talking about the drag in terms of vertical movement. This is why you do a horizontal flare if you somehow find yourself in an uncontrolled ascent.

However.... You know how the amount of power needed to overcome drag increases as the cube of the increase in velocity? That works both ways: at low velocities the amount of power needed to overcome drag is very low (going to zero at zero velocity ). In other words, for small displacements from an initial velocity of zero, the force required to overcome drag is so small compared to the force requires to overcome inertia (for massive objects like scuba divers) that it can basically be ignored.

Where drag very much matters is resisting current because the current means you are starting with a velocity component above zero. In that case, if you wish to minimize the effort to stay stationary (whether swimming effort or the force needed to hold a line) you will want to minimize drag in the direction of the current flow. This typically means horizontally.

But absent current, neither physics nor biology make a compelling case for choosing any particular orientation on a stop. So do what makes sense in terms of the environment of the stop (e.g. looking for boats or avoiding other divers) and your training.

 

[Blackcrusader]

I dive my Perdix in OC Tec mode even on recreational dives.

Do upgrade to the latest firmware. Also turn on the CLEAR message system which gives you a clock count after you have finished the safety stop. This will add time if you are still in the water dawdling around as I often do.