OC Dive Profiles

[Peter Bomberg]

I need some help, I am trying to determine a "normal" dive profile for a typical boat dive in a warm water env, ie the typical boat dive that is done at a resort. I know every dive is different but in your experience are you typically averaging 60ft for 60min or is 60ft for 45min more normal or 90/60 or ????

The reason I am doing this is rather silly but I am trying to see how small Bail Out tanks I can get away with on my rebreather when I accompany OC divers (AOW) and to do that I need to model an OC dive rather than a rebreather dive, yes I know that OC dive is a non deco profile so I can run every profile that stays with the deco limit and then run those trough multideco to calculate the bail out but was hoping to get your thoughts and experience.

Peter

 

[elan]

90 for 60 will be definitely deco. Per GUE guideline on 32 percent is 130 minus the depth in ft. So 30 mins at 100 ft , 40 at 90 and so on. That would be ok with min deco accend. I personally find that this is pushing the limits and I feel crappy after the dive so I pad this with 6 mind ascend from 20 ft.
Gas wise min gas from 100 ft is around 40cuf give or take.

 

[waterpirate]

If you are on a resort dive that is a group with a DM. Your dive time will be determined by the biggest hoover in the group. When hoover hits the turn pressure and signals the DM, the dive is over.
Eric

 

[Phil_C]

Where I dive most 'typical' open circuit boat dives are 25-30 metres (80 to 100 foot) for a total dive time of around 30-35 minutes - no deco and no overhead environments. Obviously as mentioned above that is dependent on greatest gas hoover limiting this if they hit the turn pressure earlier. Shallower dives with less experienced divers don't tend to go much over the 35 minutes either. Guess this just fits their business model with fitting a certain number of dives per day. P

 

[victorzamora]

I think it greatly depends on where you're diving. In the keys, you typically get up to 50min in shallow water (30ft or so) on the reef dives. In Roatan, most dives drop straight to 80ft, and you do a slow climb after a short bottom time...total dive time is typically 45min. NC wrecks have a square profile, so something more like 80ft for 17 minutes is pretty common.

 

[Peter Bomberg]

Thanks based on the above I only need 10Cft of Bail out and since I like 33% or higher buffer I round that to 14Ft and since I like to be balanced that leads to double 13 or 19's (perfect as they are small and very light weight (Carbon Fibre tanks).

Now all I need to do is to convince the local dive shop to let me dive using a rebreather while everyone else is on an OC, but that is normally not an issue as long as they see an OC bail out system and a DM card)

 

[Wookie]

Having logged thousands of divers on and off, 80 for 40 is by far the most popular dive. That is 80/20 bottom time with a 20 minute ascent. I think that's what you are looking for is a simple answer?

With that said, I have logged hundreds of rebreather divers off the boat while on recreational profiles. To a person, they used a 40 to bailout. I've seen a SD EVO+ on a travel frame with a 19 strapped to it, it was pretty cool, but I've never seen a RB go into the water with anything but a 40 BO.

 

[DBailey]

Most of my resort dives come in at the average depth in the 45-55 range with a bottom time of 45 minutes. I'd be willing to bet that Wookie's 80 for 40 is close to the same on the average depth.

 

[rongoodman]

As a new rebreather diver, the only bailout tank I would use other than a 40 would be a 72/80.

 

[Peter Bomberg]

Thanks Guys,

Yes I admit I am looking for a simple approach (I know I can always run the numbers and will but am looking for a good versatile config).

Ok curiosity killed the cat, why would you guys use a 40 BO on a CCR rather than smaller say 20?

If I am renting a tank yes it will be a 40 or 80 as that is what resorts have but if using my own I am leaning towards dual CF 17's, so now I am curious why you guys prefer the 40?

Peter