re: Freon

Are you looking to use Freon for the torpedoes or for the ballast system?

In the case of torpedoes, you pretty much have to use a liquified gas as your replacement for Freon. It\'s the only way that you will get any kind of reasonable run time out of the torpedoes. Joe B. has given a good response as to using airbrush propellant, e.g. Propel.

If you are asking about the ballast system, compressed air could be used but you might need to make a few modifications. In the typical gas ballast system, the holding tank contains enough liquified gas (Freon, Propel, CO2) to give you at least a handful of full ballast blows before needing to refill the tank. If the tank were to be filled with compressed air, you will likely only get 1 or 2 complete ballast blows before needing to refill the tank. This assumes no modifications are being made to the ballast system. While it\'s certainly possible to use some very high pressure compressed air, the tradeoff in cost to refit the system with high pressure fittings is hardly worth it. At that point, you would be better of going to something like CO2 and using off-the-shelf components like tubing and regulators that are known to be approved for liquid CO2 service.

There are several ways to use compressed air in both open and closed systems. The Engel piston and one form of the pump boats are good examples of closed systems in that the air in the ballast tank/piston is not vented to the outside....it\'s retained onboard and compressed.

In an open pump system, a pump is used to move air and water into and out of the bllast tank...but the big caveat here is that to move air into the ballast tank you need to have something that sticks above the water\'s surface.....just like a schnorkel. If you cannot drive the boat up to near the surface of the water.....you don\'t have a way to empty the ballast tank.

-hope thsi helps!

Jeff