Dive Planning and sequence...

jasonmh · December 29th, 2005, 12:11 AM

Sorry if this is in the wrong forum, I tried to pick the one that seemed to match closest.
Most open water training agencies teach that if you are planning a multiple dives a day, that you should do your deepest dive first then the shallow dives. I have heard from DIR divers that say that obviously this is wrong and that you need to do the shallow dives first then the deepest, but with no explanation as to why.
Is this true, and if so why? Does the sequence of the diver matter relative to depth. Or am I wrong and these are rumors I am spreading?
Thanks All,
Jason

JimC · December 29th, 2005, 12:51 AM

http://www.wkpp.org/articles/Decompr...tive_dives.htm Not totaly clear, but what I get from that is that if you do your first, shalow dive correctly it has no impact on your schedual for your second, deeper dive.

LCF · December 29th, 2005, 01:31 AM

Note that he is talking about deep dives on trimix with multiple gas deco finishing on 100% O2. I don't think you can use the same reasoning to recreational OW dives, even done on nitrox.

JS1scuba · December 29th, 2005, 07:55 AM

Quote: (Originally Posted by jasonmh)

Sorry if this is in the wrong forum, I tried to pick the one that seemed to match closest.
Most open water training agencies teach that if you are planning a multiple dives a day, that you should do your deepest dive first then the shallow dives. I have heard from DIR divers that say that obviously this is wrong and that you need to do the shallow dives first then the deepest, but with no explanation as to why.
Is this true, and if so why? Does the sequence of the diver matter relative to depth. Or am I wrong and these are rumors I am spreading?
Thanks All,
Jason

The classic approach to no-stop diving is to do the deeper dive first and then the shallower dive. The reason is that you will not have sufficient no-stop time for a deep 2nd dive if you did the first shallower dive to the no-stop limit.

However if you are conducting a dive that will have decompression it makes no difference the sequence so long as the decompression is complete. And, if you are using the proper decompression gases.

For a true techincal dive that uses helium and deco gas and oxygen, here is also makes no difference on the sequence so long as you used oxygen for the 10 and 20 fsw stops and your surface interval is 3 -5 hours. Though it is wise to plan the 2nd dive to be five minutes shorter than the first one. This has just been our practice over the years.

Cheers

Joe Hesketh · December 29th, 2005, 12:45 PM

Reverse profiles are a bit of a myth in the recreational arena as well. Have a read of this for a review of the Smithsonian Institute's conference on the subject. The general recommendations are likely to stay the same but there's no real reasoning for it.

There's some real misinformation about this rule of thumb though. A couple of years ago in the Red Sea, our dive guide said, "OK, the dive we have planned for this afternoon is 25m, so this morning we'll have to go to at least 26m to get the depth...". I remember thinking WTF! I guess it was for liability/employer reasons that the guide wasn't allowed to log reverse profiles for her boat. But this kind of sh*t is being pumped out to people who might believe that it in someway places them at a deco risk if they don't go deeper on the first dive

December 29th, 2005, 12:11 AM	#1 (permalink)
jasonmh(Offline) New Member Join Date: Nov 2005 Location: New Mexico Posts: 125	Dive Planning and sequence... Sorry if this is in the wrong forum, I tried to pick the one that seemed to match closest. Most open water training agencies teach that if you are planning a multiple dives a day, that you should do your deepest dive first then the shallow dives. I have heard from DIR divers that say that obviously this is wrong and that you need to do the shallow dives first then the deepest, but with no explanation as to why. Is this true, and if so why? Does the sequence of the diver matter relative to depth. Or am I wrong and these are rumors I am spreading? Thanks All, Jason

December 29th, 2005, 07:55 AM	#4 (permalink)
JS1scuba(Offline) New Member Join Date: Nov 2005 Location: Arizona, USA Posts: 82	Quote: (Originally Posted by jasonmh) Sorry if this is in the wrong forum, I tried to pick the one that seemed to match closest. Most open water training agencies teach that if you are planning a multiple dives a day, that you should do your deepest dive first then the shallow dives. I have heard from DIR divers that say that obviously this is wrong and that you need to do the shallow dives first then the deepest, but with no explanation as to why. Is this true, and if so why? Does the sequence of the diver matter relative to depth. Or am I wrong and these are rumors I am spreading? Thanks All, Jason The classic approach to no-stop diving is to do the deeper dive first and then the shallower dive. The reason is that you will not have sufficient no-stop time for a deep 2nd dive if you did the first shallower dive to the no-stop limit. However if you are conducting a dive that will have decompression it makes no difference the sequence so long as the decompression is complete. And, if you are using the proper decompression gases. For a true techincal dive that uses helium and deco gas and oxygen, here is also makes no difference on the sequence so long as you used oxygen for the 10 and 20 fsw stops and your surface interval is 3 -5 hours. Though it is wise to plan the 2nd dive to be five minutes shorter than the first one. This has just been our practice over the years. Cheers __________________ Joel Silverstein, VP, COO www.techdivinglimited.com a division of Scuba Training and Technology Inc. NAUTILUS DIVE PLANNER CYLINDER SPEC CHART

December 29th, 2005, 12:51 AM	#2 (permalink)
JimC(Offline) New Member Join Date: Nov 2005 Location: Ottawa Posts: 18	http://www.wkpp.org/articles/Decompr...tive_dives.htm Not totaly clear, but what I get from that is that if you do your first, shalow dive correctly it has no impact on your schedual for your second, deeper dive.

December 29th, 2005, 01:31 AM	#3 (permalink)
LCF(Offline) New Member Join Date: Dec 2005 Location: Seattle Posts: 623	Note that he is talking about deep dives on trimix with multiple gas deco finishing on 100% O2. I don't think you can use the same reasoning to recreational OW dives, even done on nitrox.

December 29th, 2005, 12:45 PM	#5 (permalink)
Joe Hesketh(Offline) New Member Join Date: Nov 2005 Location: London, UK Posts: 657	Reverse profiles are a bit of a myth in the recreational arena as well. Have a read of this for a review of the Smithsonian Institute's conference on the subject. The general recommendations are likely to stay the same but there's no real reasoning for it. There's some real misinformation about this rule of thumb though. A couple of years ago in the Red Sea, our dive guide said, "OK, the dive we have planned for this afternoon is 25m, so this morning we'll have to go to at least 26m to get the depth...". I remember thinking WTF! I guess it was for liability/employer reasons that the guide wasn't allowed to log reverse profiles for her boat. But this kind of sh*t is being pumped out to people who might believe that it in someway places them at a deco risk if they don't go deeper on the first dive