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Hi Hugh. Yes, that's my understanding of the ABS guidelines as well.
Soooo......on my sub, I have a 1 inch elbow sticking out of the top of the
ballast tank, connected via a short rubber hose to the thru-hull nipple which
has a 1 inch ball valve threaded onto it just inside the hull.
This line goes up to the top of the sub hull where there's a "T" for
injecting HP air into the line for back filling into the tank.
The other end of the "T" goes to another 1 inch ball valve that is threaded
onto the thru-hull nipple mounted vertically in the top of the sub. To dump the
air and flood the ballast tank, I need to open BOTH 1 inch valves so the air can
exit the ballast tank, go through the line and exit the sub through the top vent
nipple.
Now, if I want to "blow ballast" I first close off the upper vent valve,
open the HP air line feeding into the line leading to the open valve/nipple at
the ballast tank. Once the bubbles show that all the water in the tank is out,
shut off the HP air valve and close the lower vent valve. Now thw air is trapped
in the ballast tank.
If for some reason there's a problem with the line, I can close the nipple
valve at the tank, open the nipple valve at the top of the sub, and blow some
air through the line to clear it.
Now with all the valves inside the sub, I can disconnect the plumbing all
except for the two valves directly on the thru-hull nipples, and affect a repair
like a small leak of a threaded connection, and put it back together while still
submerged. Or, I could reconfigure the plumbing inside to get air from another
source or to make the air/water flow some where else if needed.
This scenario isn't likely to happen, but it COULD be done if needed.
The other ballast tank is a copy of this one. ( one in front, one in
back.)
I had originally planned on 4 ballast tanks, but soon
realized that is not needed, as long as I balance the sub left to
right.
I will have a sliding weight under the floor to change dive angle, operated
with a rocker switch and electric actuator. The same kind as I'm using for
external dive planes and rudder control, except it won't need to be oil
compensated. Again, if I keep all the parts the same, carrying spares will be
easier. Frank D.
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