Tank sizes when diving

[MSDT476614]

The more expensive the boat trips become the more prevelant larger tanks wil be. $200+ for 2 20 min dives is pretty costly. 400 if you are paying for your buddy. so why not make it 2 40 min dives. As long as you can buddy up with someone with like volumn and watch your ndl, there is no problem. WE all know that does not describe all divers. I have had boats tell me i can not take a lp120 on thier boat. My lp95's have always been accepted. I also see boats calling for back on board with 1000 psi and starting accent at 1500 for a 90 ft dive and actually checking psi when getting back.

Thanks KWS! So economics drive part of the bahaviour. Why can't you take 120s on board if those are your own tanks? Back on board with 1/3 may be conservative but may I ask where you dive? Sometimes sea and surface conditions ask for some conservatism. Some may say 1500 to turnaround defeats the 1/3 rule for safety where the turnaround should be at 2000?

Checking psi - I do that post dive for all divers as a matter of record and allow SAC computation rather then to see if they've adhered to the 'briefing.' Some 'older school' operators do that - helps us note who to place closer to us or keep an extra eye out for as buddy teams in the water when we lead dives so that we can share air if necessary? Or just simply who to buddy with whom so the next dives are the most productive?

 

[bpotkin]

I purchased a hp100 steel tank based on recomendations. I was told by dive pros that it was the best overall tank
for obvious reasons.

 

[fnfalman]

Why do people even care about what tank sizes others use?

Should I laugh at those double-tank divers?

 

[MSDT476614]

;D

I don't care what other's use. I'm concerned about what I provide and how it generates risk for the dive professionals leading these divers.

The safety of my pros is my concern as is the safety and comfort of divers who come with us.

Limitations on tank / equipment renters provides some degree of risk aversion. I'm trying to balance risk and 'comfort.' Our normal dives on 80s are in excess of 60 minutes of which all our pros can easily hit deco limits on most comps at 30m/100ft. It is debatable if we want our divers to do that.

 

[NAM001]

the fear is that 120's would allow you to exceed ndl and still get onboard with the designated psi. some boats want to use one model for gas consumption. the standard 80. sea and surface makes little difference when the model is that an s80 at 80 ft will produce a 20 min dive for everyone except the 2 guys that have 120's. messes up SI's for the group also as they model s80 dive 2 hour si and another s80 dive. It would appear that you are using the psi for something usefull. if you dont exceed ndl and deco dives are not allowed because it is a recreational based, milti dive, group based, dive plan then the 120's are a problem to the boat operators. Finally , to newer divers, larger tanks are the answer to bottom time, they indicate you can go deeper and longer before hitting accent psi. It goes along with boats not allowing other than single tank rigs. I dont have problems with them cause i call first and ask what the tank limits are, so all is well. ITS THIER BOAT. A slight overfill on an lp95 is a lot of air. compared to an s80.. many times i have surfaced with 15-1800 on a lp95 and the insta-buddy with s80 is at 500 so its no biggy. Still plenty of air to share if needed. The greatest latitude in tanks was when one group (club) did a trip. we had doubles you name it. Normally a mixed group is more stringent to the s80's. Besides you dont fnd to many boats that can hold 8" tanks. Sand dollar out of coz would only allow thier s80's, Another place would allow the 120 but charged double for a fill whether it had 1800 in it or 300 so they advised to not bring them for that reason and they could not stage that large of tank with the group size.

Thanks KWS! So economics drive part of the bahaviour. Why can't you take 120s on board if those are your own tanks? Back on board with 1/3 may be conservative but may I ask where you dive? Sometimes sea and surface conditions ask for some conservatism. Some may say 1500 to turnaround defeats the 1/3 rule for safety where the turnaround should be at 2000?

Checking psi - I do that post dive for all divers as a matter of record and allow SAC computation rather then to see if they've adhered to the 'briefing.' Some 'older school' operators do that - helps us note who to place closer to us or keep an extra eye out for as buddy teams in the water when we lead dives so that we can share air if necessary? Or just simply who to buddy with whom so the next dives are the most productive?

---------- Post added December 14th, 2012 at 11:59 PM ----------

You just reinforced my above post. The only difference is that you opinion is usually the opinion onf the boat. Many of the boats I have been out on do not provide a DM in the water, Our group I guess you would say goes without a waterborn DM and the boat is just for transportation and body counting and dive plan management.

;D

I don't care what other's use. I'm concerned about what I provide and how it generates risk for the dive professionals leading these divers.

The safety of my pros is my concern as is the safety and comfort of divers who come with us.

Limitations on tank / equipment renters provides some degree of risk aversion. I'm trying to balance risk and 'comfort.' Our normal dives on 80s are in excess of 60 minutes of which all our pros can easily hit deco limits on most comps at 30m/100ft. It is debatable if we want our divers to do that.

 

[MSDT476614]

the fear is that 120's would allow you to exceed ndl and still get onboard with the designated psi. some boats want to use one model for gas consumption. the standard 80. sea and surface makes little difference when the model is that an s80 at 80 ft will produce a 20 min dive for everyone except the 2 guys that have 120's. messes up SI's for the group also as they model s80 dive 2 hour si and another s80 dive. It would appear that you are using the psi for something usefull. if you dont exceed ndl and deco dives are not allowed because it is a recreational based, milti dive, group based, dive plan then the 120's are a problem to the boat operators. Finally , to newer divers, larger tanks are the answer to bottom time, they indicate you can go deeper and longer before hitting accent psi. It goes along with boats not allowing other than single tank rigs. I dont have problems with them cause i call first and ask what the tank limits are, so all is well. ITS THIER BOAT. A slight overfill on an lp95 is a lot of air. compared to an s80.. many times i have surfaced with 15-1800 on a lp95 and the insta-buddy with s80 is at 500 so its no biggy. Still plenty of air to share if needed. The greatest latitude in tanks was when one group (club) did a trip. we had doubles you name it. Normally a mixed group is more stringent to the s80's. Besides you dont fnd to many boats that can hold 8" tanks. Sand dollar out of coz would only allow thier s80's, Another place would allow the 120 but charged double for a fill whether it had 1800 in it or 300 so they advised to not bring them for that reason and they could not stage that large of tank with the group size.



---------- Post added December 14th, 2012 at 11:59 PM ----------

You just reinforced my above post. Many of the boats I have been out on do not provide a DM in the water, Our group I guess you would say goes without a woterborn DM and the boat is just for transportation and body counting and dive plan management.

Thanks much again KWS! Appreciate your insights.

Trying to figure out how to handle divers who know what they want and think they know what they want as well as just want because its less work on skills such as bouyancy/breathing/finning but at the same time balance our dive operations as you mentioned about plans and SIs.

 

[NAM001]

I dont hink you can easily. That is why most boats go out for a purpose ie rec dive no deeper than 100'. Now i have been on many flower gardens trips and that is the way it is done. 5 dives a day including a night dive. With that degree of repeated dives you have to set limits and enforce them. We have in the past chartered a gardens trip that would be a nitrox trip. The Group DM and the boat developed a dive plan and established new SI's ect to accomodate the O2 levels being used. But still the group as a whole had one set of rules to comly with. While the divers are in water they note time of first in and time of last out ans call that period the botom time for everyone. when we get out they note time psi and max depth. the deepest depth was given to all for Determining the SI. So when everyone useds the same tank which equates to similar bottom time and the deepest diver is used for group depth, a level of conservatism is injected in to the system.

On a 5 dive day (9 dive trip)its in water at 7 out at 8 si till 10 in water at 10 out at 11 si and change location till 1. in water at 1 out at 2 si till 4 in at 4 out at 5 si till dark say 9pm and in water for night dive at 9 out at 10. Then night transit and sleep to new location and do 4 more dives the next day and back to port. Granted this is a much more complex evolution in planning that a 2 tank dive. But it still rellies on haveing some basic constants like tank size.

Thanks much again KWS! Appreciate your insights.

Trying to figure out how to handle divers who know what they want and think they know what they want as well as just want because its less work on skills such as bouyancy/breathing/finning but at the same time balance our dive operations as you mentioned about plans and SIs.

 

[Tigerman]

;D

I don't care what other's use. I'm concerned about what I provide and how it generates risk for the dive professionals leading these divers.
...

Id say theres ALWAYS less risk having more gas. Yeah, you may push your NDLs with more gas, but if youre paying THAT little attention to your computer/gauges/timer I would say that you shouldnt be in the water given you probably dont mind your depth or air either...

 

[CT-Rich]

My 2 cent. New divers tend to buy gear on the type of diving they intend to do.... when they start. A lot of Newbies plan on wreck and tech without know really having all that much understanding of what is REALLY involved, The time, the training, the cost of boat charters and maintaining gear. I say buy what you want. The only stipulation on tank size is that don't go bigger than you can handle on land or boat.

The nice thing about Newbies with expensive tastes is that they flood the used market with good gear. I just picked up a SP Nighthawk w/air2 and a SP MK25/G250hp reg for only $300 from someone that wanted to be Lloyd Bridges, then didn't have the time or interest.

By the way, my go to tank is a steel 100, just like the way is dives, much nicer than AL 80

 

[LaMissJude]

yes sir! I'll inform my female DMs who average 5' tall and 100lbs to bulk up right now.

As a pro diver and a woman that is 1m62 tall and 55kg (5'3 and 121 pounds, I checked on internet as I'm really not used to this system ^_^) working in a tropical country, I LOVE 10L al that you can fill to 230bar. It is great!!!
It is not behind my knees as classic 11L al, and it still leaving me enough air at the end of the dive in case of problem for a guest (I usually come up with between 90 bar to 120 bar left in my tank, depends if it was filled to 200 bar or more.)
If you don't have some of these and if you can have it where you are, I'm pretty sure your small lady DM will be very happy with these thanks