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Hi Group,

I have come across a question for which I would really appreciate some help 
from those on the list who are experienced in planning cave dives using 
scooters.  And I believe that there are probably some of the most 
knowledgeable scooter divers in the world on this list.  The question deals 
with how many safety cylinders I need to stage in a cave and how close to 
each other they need to be.

For our particular situation I can give the following information, and if in 
the future this information should change, I can adapt the answers we 
determine here now.  I am purposely using conservative numbers because, as I 
have said in the past, I have this wide yellow streak running down the center 
of my back when I'm diving in an unfamiliar overhead situation.  And 
exploring our "New Little Cave" in Belize, when we're more than a half mile 
in, is such a situation.

The following figures might be typical to use.

Scooters:    (2) Oceanic Mako's running @ 2 mph with an 80 min. burn time.
Divers:        Both divers with RMV's of 0.6 cu.ft./min. swimming @ 0.5 mph 
and 0.4 cu.ft./min. riding
Back tanks: Double 85's filled to 3100 psi. yielding 200 cu.ft.
Drop Tanks: 80 cu.ft. aluminum's pumped to 3300 psi.
Cave:          Drops rapidly and runs fairly horizontal @ 70 - 85 ft., lets 
say no current for now.
Deco gas:    Oxygen tanks can easily be staged at the cave entrance.

The scooter cave dive planning rules with which I am familiar require 
assuming both scooters die at the point of deepest penetration, requiring a 
swimming exit.  And subsequently the dive becomes a typical cave dive, so I 
must have enough gas for both myself and my buddy to exit.  The planning for 
this, should it be felt that this is the correct approach, is straightforward.

But if we have staged tanks as we plan to, they might be, say, 1,500 ft. 
apart.  And I'm interested in opinions as to how many tanks need to be at 
each station.  I assume our planning would be such that we could get to the 
first set of tanks with 1/2 of our back gas remaining, but then do we need to 
have 2 or three tanks waiting?  And at each station along the way 
subsequently, do we need 2 or three tanks?  Or has it been found acceptable 
to consider our remaining back gas to be enough of a safety factor in case 
there is a problem with one of the drop tanks.  (Seems reasonable to me, but 
I'm just checking.)  I feel that I can't plan on our support divers, being 
cave students I certified about a year ago, penetrating much deeper than 1/4 
mile into the cave.  And since this is not a supported project, most of the 
money I can spare has gone into buying the two Mako's, so I can't afford any 
more right now.

My guess, from the GPS readings of the cenotes with which we are familiar, is 
that we probably will not need to penetrate more than 1.5 to 2 miles before 
we come out another entrance.  But as this is only what I assume (which can 
easily make an ASS of U and ME), I'd like to get my contingency planning in 
order.  I realize that the deeper penetrations, if necessary, may necessitate 
additional planning to accommodate the scooters' burn times.

So any thoughts on planning this type of dive would be gratefully 
appreciated.  I figure that there is probably more experience with scooter 
usage in cave diving on this list then just about any other place with which 
I am familiar.  Thanks a bunch for your time.

Take care and safe diving,     Scott

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