equipment configuration

[DA Aquamaster]

I'll second what Doc Intrepid suggested about the Auqa Explorer's "travel tands". They are practically made to order for the trip you are planning and add a great deal of saftey and redudancy for only a few pounds of weight and an extra regulator.

In my opinion the question of whether a 200 ft dive can be made safely on an AL 80 with or without surface supplied air for the deco stops is irrellevent. If you can easily use a pair of independent doubles for increased saftey and redundancy, why wouldn't you? It quick, easy, effective and gives you the confidence of knowing you have all the gas you need to do your deco obligation if you manage to get separated from the boat.

Independent doubles also feel a lot better in the water and are much more natural to dive than the single tank with an 80 cu ft stage bottle that someone suggested. You still need 2 regs either way so just add the bands and make it as much like a normall doubles dive as possible and avoid having an assymetircal configuration and a bulky AL 80 under an arm.

I am not opposed to a deep air dive to 190 feet or so but I do feel that a deep air diver's in water skills need to be automatic and second nature and that a deep dive is something you need to work up to. I firmly believe a diver develops a tolerance for the higher levels of narcosis that are encountered by doing frequent dives to progressively deeper depths. Some people object to the concept of tolerance, so maybe the ability to accomodate for the narcosis related impairment at depth is a easier concept to accept.

 

[beche de mer]

I'll second what Doc Intrepid suggested about the Auqa Explorer's "travel tands". They are practically made to order for the trip you are planning and add a great deal of saftey and redudancy for only a few pounds of weight and an extra regulator.

Thanks for that advice. Yes, that does seem a simple way to greatly increase the safety margin at very little cost and weight penalty, and I intend to look into it.

To get back to the issue of the Coolidge on a single tank, someone produced some calculations a while back, purporting to show that the idea was BS. Imperial figures are confusing. We use metric over here. Here's my calculations:

Let's say we have a tank with water capacity volume 10 litres. When filled, that's 2,000 litres of gas. (80-90 cu ft.)

The stern is say, 60 metres. (7 atmospheres)
The bows are 25 metres. (3.5 atmospheres)
So the average depth for the return leg of the dive is 40 metres - which is 5 atmospheres.

Let's use a SAC of 10 litres/min, which is about right for me in wam water with not much weight encumbrance. (To be determined beforehand, of course.)

The tour begins at the stern, where you might spend 5 minutes. (5 min x 10 litres x 7 atmospheres = 350 lites of gas used at the stern.

Then 20 minutes to the bows, at average depth 40 metres, is 20 x 10 litres x 5 atmospheres = 1,000 litres. (That's a slow swim - 200 metres in 20 minutes.)

Total consumption ~ 1350 litres. So you get back to the bow with a third of your gas left.

Unlikely you would be able to do your total deco on this, but you don't need to, as deco gases are tethered at the rail.

The figures are approximate, and descent gas hasn't been factored in, but allowing +/-20%, they're still OK.

The main dangers for these dives, in my opinion, would be first stage failure, (which could be catastrophic) - and for the penetration dives - losing your guide. There have been deaths on the Coolidge, but not for either of those reasons.

 

[newdiverAZ]

now this is totally insane!!!!
200' = 7 ata assuming sac rate "at rest even" of .5 this equals 3.5 cfm
20 min bottom time = 70cf from a 77.4 cu ft tank,assuming you could make it to any deco stop, even skipping deep stops you'd need another 24 cu ft to do 30 mins @ 20'.not counting ascent time you'd use 104.4 cu. ft of gas without leaving anything for oops or your buddy.I'm making a note not to dive with you, if i had a problem I'm dead.plus hope ya got a scooter with them figures you can't allow for finning lol

On air.
Usually about 20 minutes touring and 20-30 minutes deco.
80 cu ft. tanks.

In the warm, clear waters, gas consumption is surprising low.

Deco-ing is done on the deco terraces, which are 2 flat areas in the coral, just inshore from the bows. There are fixed bars you can hang on to if you like, or stick your fins under. 9 months of the year you'll have Boris for company - a tame grouper, about the size of a pony. (He loves being stroked.)

There is tethered gas at the deco stop. You can ask for EAN50 if you want it.

Voop asked "Where was this wreck again".

It's in Vanuatu, a group of islands to the east of the Solomons. The specific location is the island of Santo, which was a major staging area for the US campaign in the Solomons.

There's lots of interesting history surrounding the Coolidge which, prior to being commandeered as a troop carrier, was a luxury liner with the Dollar Line. The sinking is an interesting tale, with loss of life and acts of heroism.

 

[newdiverAZ]

guess i should have read to the end before posting lol

 

[newdiverAZ]

i get about a 160 min run time on that profile assuming air, better sling alot of 80's 206 cu ft worth just for you

 

[d33ps1x]

You could just do what you want I guess.

I'm guessing these guys are more concerned about you than just being nasty.

Good luck on the dive.

 

[voop]

I'm curious why you would choose for this instead of a double-10. Care to go in to that?

R..

Of course I will go in to that

It's really very simple: I own an 18l, but I do not own a twin-setup...yet, that is.....

A twin set w. manifold and 2 1.stages is more redundant than a big tank with a H-valve and 2 1. stages. No argument from me there....

 

[Cudabait]

Beche,

Hey, Doc, I may be mistaken but I think you are trolling. As a medical practicioner and advanced nitrox diver you should know better. Others have asked for additional skills you may have in order to help. If there are none, you probably should consider another operator. It would seem you are not trained to do deco dives. Based on what you have written, it woulld appear you are about to do deco diving in a remote area, with insufficient equipment and with an operator who sponsors this type of activity. If you're not trolling, consider finding another operator.

Regards,

 

[Straggler Dave]

Beche De Mer, I notice you're from Melbourne... If you don't mind me asking, who did you do your Adv Nitrox course with and who do you normally dive with?

I've done a few light deco dives to 35-40m (and one as deep as 48m) using a 63cf stage bottle for redundancy, which I found to be satisfactory. However I wouldn't be recommending that for diving to 60m....

 

[beche de mer]

Beche De Mer, I notice you're from Melbourne... If you don't mind me asking, who did you do your Adv Nitrox course with and who do you normally dive with?

I've done a few light deco dives to 35-40m (and one as deep as 48m) using a 63cf stage bottle for redundancy, which I found to be satisfactory. However I wouldn't be recommending that for diving to 60m....

Hi Dave. Other than saying I did it with an IANTD shop, I won't go into specifics because I'm not pretending that the dives discussed in this thread comply with orthodox teachings.

I usually dive off Portsea. We may have been in the same boat together. I always follow the rules when I'm at home.

63 cf sounds like a lot of redundancy. When I did my deep-air training (also to about 40 metres - familiar with Winged Sub?) - I used a 3 litre pony bottle slung on the front. That would be about 22 cu ft. In addition to the big 14 litre on my back. (~103 cu ft)

Yes, we observed rule of thirds, and no, it didn't give us much time for our drills.

By the time I got around to advanced nitrox, I had twins, and used the pony for deco mix.

(At the risk of further flaming - the rule of thirds is a sound rule but more applicable to actual penetration than virtual overhead. If you have clear water, zero current, a small site, (such as an aircraft), bending the rules might be OK - especially if you have your deco mix waiting for you at the top of the line. I'm not endorsing this. Just stating that the rules don't necessarily have to be slavishly followed. Understanding the risks and making an informed judgement is more important. )