equipment configuration

[Jim Baldwin]

I read with a great deal of interest your upcoming diving trip.

I have been diving for over 20 years and also have tech certifications from IANTD and PADI.

I would recommend that you reconsider your deep dives and exceeding your no deco limits.

First of all, with only a single tank and operating off the rule of thirds you are going to have a very short dive. If you are counting on a sling tank be it a pony bottle or an aluminum 80 as your stage/deco gas you are taking a deadly risk.

Usually on your stage bottle you would have a higher Oxygen mix say 50 percent to use as a travel gas. At 20 feet it's routine to switch to oxygen either 80 or 100 percent to help with your deco obligation which requires yet another bottle.

Without the proper training this is called a "trust me dive."

Do the right thing and get the training and then go put your training to good use.

Jim
Louisiana

beche de mer once bubbled...
I'm taking a dive vacation in February and I'd be interested to hear what sort of equipment configuration people would advise.

It's a live-aboard in tropical waters and the dives will be a mixture of multi-level coral dives and deep flat-bottomed dives (WW2 wrecks), during which we'll be exceeding non-deco limits. Taking doubles is not an option.

Thanks in advance.

 

[voop]

Jim Baldwin once bubbled...

First of all, with only a single tank and operating off the rule of thirds you are going to have a very short dive. If you are counting on a sling tank be it a pony bottle or an aluminum 80 as your stage/deco gas you are taking a deadly risk.

Usually on your stage bottle you would have a higher Oxygen mix say 50 percent to use as a travel gas. At 20 feet it's routine to switch to oxygen either 80 or 100 percent to help with your deco obligation which requires yet another bottle.

Without the proper training this is called a "trust me dive."

Do the right thing and get the training and then go put your training to good use.

Well, one could simply fill the stage bottles or the slig'ed 80 with the same as the backgas. That would make the only complication the gas management and the requirement to swap regulator once the slung bottle is empty. Makes it less of a "trust me" issue...

Besides, I do believe that the org. poster had IANTD adv. nitrox training, so he should know 'bout various gasses....

 

[beche de mer]

As an aside, I wonder if anyone on this thread has dived the Coolidge in Vanuatu. If you think my project is nuts, the Coolidge would make your hair curl.

It's a 20,000 ton US WW2 troop carrier (converted liner) which hit one of its own mines while entering Lougainville harbour. Bows are on the reef at 25 m, stern on the sand at just over 60 m. It's like entering a big underwater hotel, lying on its side.

Standard practice is single tank, no stage/pony/bailout, full penetration with guide. Night dives available, if you like.

That wreck would be dived pretty much every day of the year. Incidents are rare.

I'm not advocating this. Just mentioning it.

 

[SeaJay]

200' on a single tank, with no other options?

Are these dives on air?

How much bottom time are people getting?

How are they decoing? What gas are they using?

What size tank are these people diving?

 

[voop]

beche de mer once bubbled...
As an aside, I wonder if anyone on this thread has dived the Coolidge in Vanuatu. If you think my project is nuts, the Coolidge would make your hair curl.

It's a 20,000 ton US WW2 troop carrier (converted liner) which hit one of its own mines while entering Lougainville harbour. Bows are on the reef at 25 m, stern on the sand at just over 60 m. It's like entering a big underwater hotel, lying on its side.

Standard practice is single tank, no stage/pony/bailout, full penetration with guide. Night dives available, if you like.

That wreck would be dived pretty much every day of the year. Incidents are rare.

I'm not advocating this. Just mentioning it.

....but I'd probably at least (i) go with an 18l 200 bar tank rather than the AL80, (ii) sling at least a 6l deco bottle. I'd probably also do multiple dives on that boat -- sounds like an outside tour would be impressive too, in addition to the penetrations.

Of course, twins would be my preference....

Where was this wreck again?

 

[beche de mer]

SeaJay once bubbled...
200' on a single tank, with no other options?

Are these dives on air?

How much bottom time are people getting?

How are they decoing? What gas are they using?

What size tank are these people diving?

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.

 

[SeaJay]

beche de mer once bubbled...


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

C'mon, really?

"Normal" SAC for most experienced divers is planned at around .7... With your average diver, it'd be more. But let's assume that this is an "experienced" diver. So, with this in mind...

Diver starts with 3300 psi/85.5 cuft (10% overfill). By the time he's hit 200 feet (at a fast descent rate of 50 feet/min) it's already been 4 minutes... And he's sucked down a little less than 10 cuft... And he's got 75.5 cuft left.

Less than sixteen minutes later he'd be completely empty. How is it that "normal" divers are getting 20 minutes at depth - not to mention acsent (which, from 200' would take an additional five minutes to ceiling) out of an AL80?

...Then he's supposed to deco? On the same tank?

...And if his buddy's OOA, what then? He's got no gas to donate?

Sorry... What you're saying can't possibly be true.

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

Lol... It better be super-low. I mean, "not really breathing at all" low.

You sure you don't want to revise your story?

 

[OneBrightGator]

I got the feeling from his posts that they don't deco off backgas, nonetheless... still ridiculous.

Ben

 

[d33ps1x]

You do mention deco gas up to EAN50 tethered to bars at a deco stop but....

AL80 for 20 min @ 200' with a SAC rate of .7 is a little slim.

Actually a lot slim. Too slim...

Doing a sim profile in Suunto Dive Manager and giving you no more than 2 minutes to hit 200' (Serious nark time), you run out of air, as in 0 PSI, at the 16 min mark using an overfill AL80.

Using a SAC rate of .55 which is middle of the road provided no tension or heavy exertion for some divers I know, (certainly not me), you can make it with no f&^ing around to a 60' stop with an ascent rate of 30 feet per minute.

This is with 190 psi to spare!!! So unless you are not breathing or you are using a scooter and breathing very little on the bottom there is no way to do this dive and safely use a rule of thirds. :wacko:

 

[hvulin]

hi,
I'm from europe so I have big problems with your measures, but if my unit converter works fine this guy is doing a 61meter descent with 12liter bottle, and makes 20min dive + 30min deco?

well I know 1-2 people who could probably do it, but they simply don't have enough suicidal feelings to do it...

Doing any dive over 30m with 12l tank is, to say the least "not smart", but saying it's a "normal" dive that they regularly do???