Total of 12 dives and already a few lessons and one almost "near miss"

[tursiops]

It was 110' to the sand so actual depth would have been 80-90' for most of it.

Excellent Nitrox 32% dive.

 

[MrBigfins]

It was 110' to the sand so actual depth would have been 80-90' for most of it.

If you werent comfortable and didnt have experience to that depth then you were correct to pass on that dive.

My reference to depth and possible lack of hard bottom was directed at saphiremind's inquiry about nitrox. It wasnt intended as criticism of you.

 

[rvojr]

I did not take it that way. It took an additional conversation to realize the depth was to the sand and depending on the ship you could be 10-30' above that. It is amazing how many nuances/caveats there are to diving and luckily I keep learning them on here.

 

[rabe]

Conditions were not great. Choppy(~1m swell) and viz <5m, but max depth was only 10m and we're in a cove. Nunubie wasn't OVERLY confident, but was happy to go ahead with it(we ARE with 2 highly experienced divers).

Classic QLD conditions then... Actually, it can get worse... But if you get used to those conditions, everything else will be a piece of cake...
Where in QLD exactly?
I'm asking because, depending on where you are located, I can tell you where to go to try your gear without risking your life...

 

[CoralSeaMan]

The weighting issue the OP and his buddy had was with getting down. My experience is that weighting is usually taught and executed with near full tanks (at the beginning of the dive/class). In fact, proper weighting has to be computed at the end of the dive (with 500 psi). Getting down is not the same as being able to stay down. In this case the OP’s buddy still felt “light” at the end of their dive.
The OP did better than many others would have in this situation. But, as others have pointed out, “Plan you dive” includes the proper prechecks. If you cannot get them done, abort the dive.

 

[BlueTrin]

The weighting issue the OP and his buddy had was with getting down. My experience is that weighting is usually taught and executed with near full tanks (at the beginning of the dive/class). In fact, proper weighting has to be computed at the end of the dive (with 500 psi). Getting down is not the same as being able to stay down. In this case the OP’s buddy still felt “light” at the end of their dive.
The OP did better than many others would have in this situation. But, as others have pointed out, “Plan you dive” includes the proper prechecks. If you cannot get them done, abort the dive.

I think you can just compensate for the weight of air. For example these guys discussed the weight of the compressed air in a cylinder:

Weight of air?

 

[CoralSeaMan]

You can compensate for it. But you still have to add enough to compensate for it in addition to being able to get down. Especially for a new diver, testing at the beginning of the dive only tells them they have enough to get down; not whether they have enough to stay down.

 

[tursiops]

You can compensate for it. But you still have to add enough to compensate for it in addition to being able to get down. Especially for a new diver, testing at the beginning of the dive only tells them they have enough to get down; not whether they have enough to stay down.

It's not that hard. You test to have enough weight to get down, and add 5 pounds to that for an AL80. The 5 assumes you will finish the dive with 500-700 psi left in the tank.

 

[CoralSeaMan]

You are right of course. The process assumes the new diver will think to check that 14 pounds is enough and 12 is not; as opposed to thinking “I can get down with 14 so I must be be properly weighted.”

 

[tursiops]

“I can get down with 14 so I must be be properly weighted.”

...for the start of the dive. But plan (and weight) for the end of the dive.