Posted by MHK on December 18, 2000 at 09:59:17:
In Reply to: Dual Tanks vs. Pony Bottle posted by Randy Medaris on December 15, 2000 at 12:40:53:
Randy,
If you are as you say planning to go to wreck alley, and by that I assume a buil up to penetration dives, than you really want to get comfortable with doubles and iso's.. This will be discussed in great length during any wreck training class, which I strongly recommend if you are considering wreck penetration..
You have received so good answers from previous posters and I would add the following:
1) I wouldn't consider penetrating a wreck without doubles. Even if you are thinking about a single tank and a *pony*, relying on your pony as redundancy I think that is ill-advised. Particlualry if you mount it using metal to metal connections which seems fashionable these days. There is a wealth of potential problem using this method. The tried and true method for pentrating overhead environments is the use of doubles and isolation manifolds. Before you advance to this stage of diving you will want to spend a great deal of time diving shallow depths using doubles and getting comfortable with the added tank. Moreover, as Kevin briefly touched on, you will want to make a decision before you buy the tanks what type of exposure suit you will be using. To the extent you dive *wet*, you would be well advised to stick with AL tanks. Should you dive *dry* you have the option of using steel tanks. What you don't want to do is dive with steel tanks while using a wetsuit. The reason for this is that to the extent you have a BC failure at depth, double steel tanks coupled with a BP will generally yield you without sufficient infaltion to ascend. The AL tanks, of course, swing to positively bouyant when they get low. The steels will remain negative but you will have the added redundancy of a drysuit to use as an inflation source.
Balancing your rig becomes extremely important when you advance to doubles. Moreover, you will want to spend time at shallow depths getting familiar and comfortable shuuting down valves and turning on and off your isolator valve. To the extent that you can't do this relatively quickly you could be asking for trouble once you start going deeper and/or penetrating wrecks.
You may very well want to rent a few different sets of doubles before you commit and buy.. Some can handle the added weight of steels, some can't.
You'll need to understand your gas requirements and decide how much volume you need..
Hope that helps..
Later