Impossibly hard scuba diving questions please

[wreckchick]

bp/w vs. jacket vs. back-inflate

R

 

[Walter]

All these questions are great, but who wants to give me answers?

Poor kid. I thought you wanted to research them.

Describe a Seche Disk.

What is it used for?

Covered here.

Who made NitrOx popular in the Keys?

Dick Rutowski

Define Benthic.

1. of or pertaining to a benthos.
2. of or pertaining to a benthon.

Is the term FSW a measure of

a) Depth
b) Pressure
c) All of the above

B

What was the first nationwide SCUBA certification agency in the US?

YMCA

Who was the first woman to head a major certification agency?

Frankie Wingert of the YMCA SCUBA Program

What is the largest shark? the smallest?

Whale Shark - Pigmy Shark

Define littoral
and sessile

1. A coastal region; a shore.
2. The region or zone between the limits of high and low tides.

1. Botany. attached by the base, or without any distinct projecting support, as a leaf issuing directly from the stem.
2. Zoology. permanently attached; not freely moving.

What's good about it?

Nothing. It's not a feature, it's a bug.

I'm leaving the rest for you.

 

[oceandjinn]

Ok why is it that if you go to a padi store they say SSI is outdated or NAUI is nonexistent from next year or any variation of the three. And secondly can you buy THE WHEEL anywhere with instructions and is it better than a dive computer and why?

 

[oceandjinn]

By the way the largest shark is my sisters baby.

 

[diverdown13]

well, I actually did want too, but I ended up having a ton of great questions, and no good answers, and then I got all backed up, got a buch of different answers for certain questions and eventually gave up.
thanks for the answers!!!!

 

[miketsp]

well, I actually did want too, but I ended up having a ton of great questions, and no good answers, and then I got all backed up, got a buch of different answers for certain questions and eventually gave up.
thanks for the answers!!!!

Ok here are mine...

A diver is in a boat in the middle of a fresh water lake.
He empties the beer cooler which contained 100lbs of ice cubes into the water.
The ice cubes float around for a while and then melt.
What happens to the level of the lake with respect to the shoreline?
a) No change at any moment.
b) Drops then rises.
c) Rises then drops.

Answer (a) Explanation. While the ice cubes are in the boat the boat sinks a little to displace 100lbs of water. When they are thrown into the water they continue to displace 100lbs of water even though they are less dense, and occupy more volume. But the excess volume sticks out above the surface. As they melt they turn into 100lbs of water. So the shoreline never moves, (other than the ripples produced).

And on a similar theme
A diver is in a boat in the middle of a fresh water lake.
He throws a 40lb steel anchor into the water.
What happens to the level of the lake with respect to the shoreline?
a) No change.
b) Drops.
c) Rises.

Answer (b) Explanation. While the anchor is in the boat the boat sinks a little to displace a volume of water whose weight is equivalent to the weight of the anchor. When the anchor goes into the water it only displaces its own volume and since its density is high its own volume is much less than the volume of water that was displaced by the anchor in the boat.

 

[The Chairman]

Mike... the weight of the anchor and rope had ALREADY been displaced by the appropriate amount of water while IN the boat. There has been no change of combined density.

 

[knotical]

the weight of the anchor and rope had ALREADY been displaced by the appropriate amount of water while IN the boat.

Correct, but once the anchor is in the water, it displaces less than its weight.
Think what happens when you add air to a lift bag to recover the anchor and get it back on the boat.

 

[knotical]

At what altitude/Nitrox% combinations do the theoretical depth effects cancel?

Find the atmospheric pressure at altitude, and add sufficient oxygen to the breathing gas to reduce the nitrogen fraction proportionally.

O2% = 1 - 0.79Pa

Where O2% is the Oxygen content of EANx expressed as a decimal.
And Pa is the atmospheric pressure at altitude, in atm.

Example: at 4000 feet elevation, the atmospheric pressure is 0.8637, which can be offset approximately by EANx32.

Caveat: This is theoretical. There are divers who use this technique to dive at altitude with sea-level air tables or computers, but I don’t know if any agency teaches it. Before anyone even considers diving this way, they should be at least Nitrox certified and keenly aware of the serious risks associated with elevated oxygen partial pressures.


Simplified derivation:

Altitude theoretical depth = (D + 33)/Pa – 33
Where Pa is the atmospheric pressure (in atm.) at altitude.
And D is the actual depth

Nitrox theoretical depth = N(D + 33) – 33
Where N is the ratio of nitrogen in the Nitrox to nitrogen in air, which could also be: (1-O2%)/0.79

Assume some depth D1 and apply first the altitude formula, and then the Nitrox formula. For the effects to cancel, we should end up at D1 again, or:

N((D1 + 33)/Pa – 33 + 33) – 33 = D1
(We just substituted “(D1 + 33)/Pa – 33” for D in the Nitrox formula, and set it equal to D1)

This reduces to:
N((D1 + 33)/Pa) = (D1 + 33), or: N/Pa = 1

As mentioned above, N is (1-O2%)/0.79, we can substitute and rearrange to get:
O2% = 1 - 0.79Pa


n.b. You can find atmospheric pressure (Pa) at various altitudes either from tables or from:
Pa = (1 – H*6.87535E-6)E5.2561
Where H = Altitude in feet
And E means: “raise to the power of”

 

[miketsp]

Correct, but once the anchor is in the water, it displaces less than its weight.
Think what happens when you add air to a lift bag to recover the anchor and get it back on the boat.

Thank you knotical.

NetDoc, if you have a problem visualising the problem with the anchor, try imagining a boat that weighs nothing. While the anchor is in it the boat will displace a lot of water whose weight is equivalent to the anchor. Once the anchor is in the water, the boat will just sit on the surface displacing nothing, while the anchor only displaces its own (small) volume.
The water level will drop wrt the shoreline.

Then as knotical suggests, add a lift bag to the anchor, fill it until the anchor is neutral and you've displaced water which will make the water level rise back up to the original shoreline.