Article: Rebreathers and cave diving

Mdemon · 17th October 2006, 09:11

Quote: (Originally Posted by JPJones)

I consider CCR the safest way to Cave Dive. But remember just as a basic open water course does not prepare you to cave dive just a basic CCR course does not either. Even with over 2500 cave dives and being a cave IT I needed more training beyond my basic course to be safe.

From this and the DrMike thread, is there a manual/book/site somewhere which lists what the extra skills required are please? Just curious - I'd like to see what else is required. I guess some of it might be useful for wrecks too...

johnv · 17th October 2006, 16:19

Quote: (Originally Posted by solocavediver)

Hi Cedric,

thanks so much for another really helpful article.

There is one point in it that I think I would be wary of myself. It is the bit about the buoyancy characteristics of the tanks remaining constant therefore you can reduce your weighting at the start of the dive. Now if all goes well, yes you can, because you will use a tiny amount of gas in CCR mode and open circuit backups will not be touched. But if you have to use your extra gas for any reason then the tanks may be just as empty at the end as on open circuit - giving a big problem if ones weighting doesn't allow to get negative when the tanks are empty

I have a solution for this which may be worthy of consideration, it works for me, but YYMV.

add blocks of foam to the tanks using snoopy loops, which are ditchable in emergency. Compressable foam works, non compressable is better. for most ccr dives your tanks stay [fairly] full and neutral, but when you need to breathe the gas, you can ditch the foam. This also helps to give steel sidemounted tanks that nice floaty arse up trim needed for long distances :-)

John

cedricverdier · 18th October 2006, 00:35

Quote: (Originally Posted by johnv)

I have a solution for this which may be worthy of consideration, it works for me, but YYMV.

add blocks of foam to the tanks using snoopy loops, which are ditchable in emergency. Compressable foam works, non compressable is better. for most ccr dives your tanks stay [fairly] full and neutral, but when you need to breathe the gas, you can ditch the foam. This also helps to give steel sidemounted tanks that nice floaty arse up trim needed for long distances :-)

John

Hi John,

Do you have a pic of your tanks with the blocks of foam (if possible underwater)? I guess you need big blocks so is it very streamlined?

Cheers

johnv · 18th October 2006, 05:55

Quote: (Originally Posted by cedricverdier)

Hi John,

Do you have a pic of your tanks with the blocks of foam (if possible underwater)? I guess you need big blocks so is it very streamlined?

Cheers

I have checked and can't find any pics. This is really a european thing (not british), I tend to do it only on 15 or 18L cylinders when I have a number to carry. if you keep the blocks fairly thin & long the result you achieve is much more streamlined than without. The attachment bar I have on my inspiration for sidemounting works fine, but when you sidemount 3 or 4 tanks, it all becomes more difficult and much less streamlined if the tanks aren't close to neutral and hang down. The speed increase noticed when scootering is significant and you can get away with less lead.

It seems much more logical to me to trim each individual item if possible so that if you need to drop it off there is less overall change in bouyancy.

decoweenie · 18th October 2006, 06:54

Another possible solution is using (intact) bicycle inner tube wrapped around the tanks so you could adjust the amount of lift u/w by adding/removing air inside the tube.

IIRC, WKPP mentioned the use of this in the past. I have no direct first-hand experience with this method, just remember vaguely that it was discussed...

jhaaja · 18th October 2006, 07:39

Quote: (Originally Posted by decoweenie)

Another possible solution is using (intact) bicycle inner tube wrapped around the tanks so you could adjust the amount of lift u/w by adding/removing air inside the tube.

IIRC, WKPP mentioned the use of this in the past. I have no direct first-hand experience with this method, just remember vaguely that it was discussed...

One quick and dirty way to control lift is to change the DPVs prop to higher rise

17th October 2006, 09:11	#31 (permalink)
Mdemon SiegeEngine II Current Rebreather/s: Inspiration Classic Home Build Other Rebreather/s: Inspiration Classic Home Build Join Date: Feb 2007 Location: SWUK Posts: 1,902	Re: Article: Rebreathers and cave diving Quote: (Originally Posted by JPJones) I consider CCR the safest way to Cave Dive. But remember just as a basic open water course does not prepare you to cave dive just a basic CCR course does not either. Even with over 2500 cave dives and being a cave IT I needed more training beyond my basic course to be safe. From this and the DrMike thread, is there a manual/book/site somewhere which lists what the extra skills required are please? Just curious - I'd like to see what else is required. I guess some of it might be useful for wrecks too... __________________ www.southwestmafia.com "Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"
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17th October 2006, 16:19	#32 (permalink)
johnv Custom Title Allowed! Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Other CCR Home Build Join Date: Dec 2005 Location: UK Posts: 132	Re: Article: Rebreathers and cave diving Quote: (Originally Posted by solocavediver) Hi Cedric, thanks so much for another really helpful article. There is one point in it that I think I would be wary of myself. It is the bit about the buoyancy characteristics of the tanks remaining constant therefore you can reduce your weighting at the start of the dive. Now if all goes well, yes you can, because you will use a tiny amount of gas in CCR mode and open circuit backups will not be touched. But if you have to use your extra gas for any reason then the tanks may be just as empty at the end as on open circuit - giving a big problem if ones weighting doesn't allow to get negative when the tanks are empty I have a solution for this which may be worthy of consideration, it works for me, but YYMV. add blocks of foam to the tanks using snoopy loops, which are ditchable in emergency. Compressable foam works, non compressable is better. for most ccr dives your tanks stay [fairly] full and neutral, but when you need to breathe the gas, you can ditch the foam. This also helps to give steel sidemounted tanks that nice floaty arse up trim needed for long distances :-) John
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18th October 2006, 00:35	#33 (permalink)
cedricverdier S21 M.I.B. Current Rebreather/s: Evolution Megalodon Other Rebreather/s: Not Bought Yet Inspiration Classic Inspiration Vision Sport Kiss Classic Kiss Join Date: Apr 2005 Location: Worldwide! Posts: 494	Re: Article: Rebreathers and cave diving Quote: (Originally Posted by johnv) I have a solution for this which may be worthy of consideration, it works for me, but YYMV. add blocks of foam to the tanks using snoopy loops, which are ditchable in emergency. Compressable foam works, non compressable is better. for most ccr dives your tanks stay [fairly] full and neutral, but when you need to breathe the gas, you can ditch the foam. This also helps to give steel sidemounted tanks that nice floaty arse up trim needed for long distances :-) John Hi John, Do you have a pic of your tanks with the blocks of foam (if possible underwater)? I guess you need big blocks so is it very streamlined? Cheers __________________ Cedric Verdier PADI Course Director, ANDI-IANTD-PSAI-TDI-DSAT-DAN-NAUI-CMAS Instructor Trainer Trimix (CCR and OC) and Cave Diving Instructor Trainer www.CedricVerdier.com DIRrebreather member
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18th October 2006, 05:55	#34 (permalink)
johnv Custom Title Allowed! Current Rebreather/s: Other CCR Home Build Other Rebreather/s: Other CCR Home Build Join Date: Dec 2005 Location: UK Posts: 132	Re: Article: Rebreathers and cave diving Quote: (Originally Posted by cedricverdier) Hi John, Do you have a pic of your tanks with the blocks of foam (if possible underwater)? I guess you need big blocks so is it very streamlined? Cheers I have checked and can't find any pics. This is really a european thing (not british), I tend to do it only on 15 or 18L cylinders when I have a number to carry. if you keep the blocks fairly thin & long the result you achieve is much more streamlined than without. The attachment bar I have on my inspiration for sidemounting works fine, but when you sidemount 3 or 4 tanks, it all becomes more difficult and much less streamlined if the tanks aren't close to neutral and hang down. The speed increase noticed when scootering is significant and you can get away with less lead. It seems much more logical to me to trim each individual item if possible so that if you need to drop it off there is less overall change in bouyancy.
(Offline)

18th October 2006, 06:54	#35 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,510	Re: Article: Rebreathers and cave diving Another possible solution is using (intact) bicycle inner tube wrapped around the tanks so you could adjust the amount of lift u/w by adding/removing air inside the tube. IIRC, WKPP mentioned the use of this in the past. I have no direct first-hand experience with this method, just remember vaguely that it was discussed... __________________ "...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..." - Rebreather World PM
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18th October 2006, 07:39	#36 (permalink)
jhaaja Custom Title Allowed! Current Rebreather/s: Inspiration Classic Other Rebreather/s: Join Date: Mar 2005 Location: Finland Posts: 883	Re: Article: Rebreathers and cave diving Quote: (Originally Posted by decoweenie) Another possible solution is using (intact) bicycle inner tube wrapped around the tanks so you could adjust the amount of lift u/w by adding/removing air inside the tube. IIRC, WKPP mentioned the use of this in the past. I have no direct first-hand experience with this method, just remember vaguely that it was discussed... One quick and dirty way to control lift is to change the DPVs prop to higher rise
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