lerpy
Contributor
I have a set of 130's that are my doubles. If you want a lot of gas and back pain get a set of those.
What Size Doubles?
- Thread starter Bigeclipse
- Start date
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KevinNM
Contributor
Bob Sherwood runs most classes in Cape Vincent, along the St Laurence.
OP
Bigeclipse
Contributor
lerpy
Contributor
If you are interested in doing some training in the St Lawrence, no harm in looking at instructors on the Canadian side as well. With the Canadian dollar what it is you will get a nice little bonus coming here.
KevinNM
Contributor
He's an instructor evaluator for GUE.
Contact and resume:
GUE Instructor résumé | Global Underwater Explorers
markmud
Self Reliant Diver--On All Dives.
Hello OP,
I think stuartv has some sage suggestions for you. I just completed the PADI Tec 40 course (a very good course for committed recreational divers, like me).
At 165 fsw, your sac conversion figure is 6. With a an estimated SAC range for you of between 1.1 and 1.5, you will blow through 9 cubic feet a minute with the upper estimated SAC rate. Your tech diving won't be very good with that kind of consumption. The suggestion for you to get into rebreather diving might be a good one if you are huffing that much gas volume.
I cross train. My SAC is between .47 and .54 depending on how thermally stressed I am (while doing my Tec 40 check-out dives, we were in cold water (48 degrees for 53 minutes on one dive) and I was wearing a wetsuit. My SAC during the deco stop was .54 (higher than my SAC for the working phase, which was .47. On the same dive).
Can you run around a city block 3 times at a fast clip and not break-a-sweat and not breath hard? Can you do 15 to 20 pull-ups? Can you do 15-20 push ups? Can you do 30 curls with a 30- 40 pound bar? If you can do those exercises, congratulations as you are minimally fit.
If you are in good physical condition, work on your buoyancy, weighting, and breathing issues.
When I do a square profile dive to 100 fsw where I run-out my NDL with EANx 32, I am aboard the boat with more than 1000 psi and sometimes 1200 psi in cold water (PST HP 100 tanks).
Don't create more problems for yourself by packing twin 100s or twin 130s to solve a gas consumption problem or a weighting/buoyancy/trim issue.
NetDoc is our resident expert on buoyancy/trim which leads to decreased gas consumption. Have you thought about a trip to the Keys? Get some advice from someone like NetDoc before you fix a symptom and don't fix the root problem.
(I apologize for making assumptions about your situation. However, I have dived with people having similar issues, and read about these issues before. USUALLY, the solutions above are the answer, not bigger or more tanks).
markm
I think stuartv has some sage suggestions for you. I just completed the PADI Tec 40 course (a very good course for committed recreational divers, like me).
At 165 fsw, your sac conversion figure is 6. With a an estimated SAC range for you of between 1.1 and 1.5, you will blow through 9 cubic feet a minute with the upper estimated SAC rate. Your tech diving won't be very good with that kind of consumption. The suggestion for you to get into rebreather diving might be a good one if you are huffing that much gas volume.
I cross train. My SAC is between .47 and .54 depending on how thermally stressed I am (while doing my Tec 40 check-out dives, we were in cold water (48 degrees for 53 minutes on one dive) and I was wearing a wetsuit. My SAC during the deco stop was .54 (higher than my SAC for the working phase, which was .47. On the same dive).
Can you run around a city block 3 times at a fast clip and not break-a-sweat and not breath hard? Can you do 15 to 20 pull-ups? Can you do 15-20 push ups? Can you do 30 curls with a 30- 40 pound bar? If you can do those exercises, congratulations as you are minimally fit.
If you are in good physical condition, work on your buoyancy, weighting, and breathing issues.
When I do a square profile dive to 100 fsw where I run-out my NDL with EANx 32, I am aboard the boat with more than 1000 psi and sometimes 1200 psi in cold water (PST HP 100 tanks).
Don't create more problems for yourself by packing twin 100s or twin 130s to solve a gas consumption problem or a weighting/buoyancy/trim issue.
NetDoc is our resident expert on buoyancy/trim which leads to decreased gas consumption. Have you thought about a trip to the Keys? Get some advice from someone like NetDoc before you fix a symptom and don't fix the root problem.
(I apologize for making assumptions about your situation. However, I have dived with people having similar issues, and read about these issues before. USUALLY, the solutions above are the answer, not bigger or more tanks).
markm
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OP
Bigeclipse
Contributor
My buoyancy is spot on with 7mm wetsuit . Hovering off the bottom a couple inches not touching being able to frog kick etc without silting out. However...I did just start drysuit diving last summer and I definitely have not perfected that yet and I fear that is where a large part of my consumption is coming from as last summer is where I really started doing deeper dives and paying attention to my air consumption. Maintaining the bubble was a big issue as well but I'm definitely getting better. As far as health is concerned...I'm not obese but I'm definitely not crazy fit. I can do the pushup and jogging stuff...pull ups...I cannot do more than 15 in a row. I have weak arms for my slightly chubby body. I'm sure health is also a part of it. I'm not looking to be the most air efficient diver. A few of the tech divers I do know are far from the fitness you describe and they seem to do all right. Again I'm not stating you are wrong and I agree I need to work on it but it doesn't mean I shouldn't try doing doubles. I'm still interested in the tech diving route and I while looking for doubles I will also be seriously looking into getting more physically fit. Thanks for the info.
KevinNM
Contributor
Reasonably heavy squats are good for handing doubles. Even a pair of 80s, getting up off a bench can be a pain at times. I know someone whose normal rig weights more than she does.
There is more to it than just what you have mentioned. A couple of things that caught my attention. "Cant reach NDL on nitrox? you should be able to and if not you should be darn close to the point that more gas on your back is unusable without going into deco. Next is the thing about you have all that gas but the buddy doesn't. Next on boats I often find NO DOUBLWES ALLOWED. Which leaves a larger single being the usable option. Some things from my limited experience. If you are not on a larger boat you will play heck getting out of the water without rolling the boat or straining the ladder mounts. Lp85's are light for doubles and that is what I have used. The other lp tanks get too heavy for me to haul. Hp 100's are the norm tanks if you can get a full COOL tank to start with. other wise you are back to about 90 cuft. I dive lp 95's mostly and my sac is between .4 and .6. If you are using al80's then you are already short because of having a 77 cuft tank. you can often get a lp tank filled to 3k so there is your 100 cuft in an lp85. my lp95's at 3k is 108. I noarmally hit the water with them at 3200. If the boats wont fill them beyond the 2400/2640 then it is no biggy because you don't have the ndl room to use the extra gas. I agree with PFCAJ that some time in the water should improve you gas consumption. If you were to get a pair of lp85's, you can double them up later if you want. Then finally the rule of thumb of use a dry suit with doubles incase of a blown wing.
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