To all those people who have contributed - many many thanks.
These comments are great and have given me loads to think about. Thanks so much for your efforts.
"Contrary to popular opinion, a pump type ballast system does not mean that you’re limited to periscope depth operation only. I’d like a nickel for every time I’ve heard “how do you surface if the air intake is below the surface?” The answer is very simple - drive the boat back up until the intake is out of water. With a fully flooded ballast tank, I can drive Albacore and Marlin to decks awash easily. And that’s using just the bow planes."
However, please note that the very first sub I built used this prinicple, and it bottomed out in an Olympic Swimming pool due to a tiny leak in the WTC. When the boat was retrieved the leak let in just 30ml of water. The boat was ballasted so a fully ballast tank meant the boat was at decks awash yet this extra 30 ml of water held the boat on the bottom. The batteries were fully charged and with plenty of power and full servo control, the boat was pinned on the bottom. I.e I simply could not drive up to snorkel depth. So unless you rig up a hybrid system a pump ballasted boat with a vented ballast tank is (I believe) -not a safe way to go.
Skip, you stated also
"While a positive displacement pump will create some vacuum in the tank against a closed intake (snorkel), just how much remains to be seen. I’d think that the pump would need a substantial amount of power to be able to remove enough water to reach the “30%” mark. But the real problem here is that any significant vacuum in the ballast tank would hold the snorkel valve (ping pong ball?) closed with enough force that gravity alone won’t be able to allow the float to drop. Some form of mechanical actuation would be required (servo and another channel) and this destroys the K.I.S.S Principle."
Thanks for this Skip, -this is where my thinking is right now. I am doing some testing next weeked or so and would be happy to share the results.
By the way Skip, the shippment you sent me on 21 October has still not arrived. Did you send this by air?
Subcommittee Member 1235