4 ft submarine

[Paul Davenport]

Greetings,

I have just bought a submarine (second hand and quite old - obviously
scratch built) which purports to be of the static diving type.

There is a small motor operated compressor from which two tubes lead. One
goes to a solid plastic bottle in the bow and the other to a rubber balloon
just behind this. Both of them are outside the pressure hull. The compressor
appears to be functioning but, at least with pressure hull unsealed, nothing
appears to happen when the unit is run.

Can anyone explain how this system might work?

Paul

[Jerry Shaw]

"Paul Davenport" <Davers00@btinternet.com> wrote:

>Greetings,
>
>I have just bought a submarine (second hand and quite old - obviously
>scratch built) which purports to be of the static diving type.
>
>There is a small motor operated compressor from which two tubes lead. One
>goes to a solid plastic bottle in the bow and the other to a rubber balloon
>just behind this. Both of them are outside the pressure hull. The compressor
>appears to be functioning but, at least with pressure hull unsealed, nothing
>appears to happen when the unit is run.
>
>Can anyone explain how this system might work?

I've never seen that kind of submarine, but I'll take a guess at how it works.

Basically, you want to displace the water out of the submarine to make it
lighter. To do this, you need to pump air into the balloon, to inflate it,
driving the air out. If you had another balloon filled with air, one would
deflate and the other would inflate, ending up with no net gain in buoyancy.
But with a solid bottle, the air from inside the bottle can be pumped into the
balloon to inflate it, without the bottle collapsing from the partial vacuum.

For safety, you probably want to start out with the balloon inflated enough to
cause the sub to float to the surface, and maybe a little more than that.
Then, when you turn on the compressor, you pump the air into the bottle,
pressurizing the bottle but deflating the balloon. With less volume of air in
the sub, it will sink. When you reverse the compressor (or maybe just turn it
off), the pressurized air in the bottle will fill the balloon, driving out the
water and letting the sub rise to the surface again.

You need to trim the sub with weights so it just barely floats on an even keel
when the balloon is inflated. Then when it is deflated, the bow will angle
down, causing it to dive. You may have to keep the motor running and use
diving planes (if the sub has them), to get the stern under, and keep it
running on an even keel underwater, as with the flotation in the bow, the
stern will try to rise during diving.

Does anyone else have a better idea on how this would work?

>Paul

Jerry