[PSUBS-MAILIST] Shackleton test report

[Steve McQueen via Personal_Submersibles]

Congrats! Thanks for the report. Sounds like you picked the right day as well : )

Thanks,
Steve

---- Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote: 
> Hi friends,
> 
> Today with Mark Ragan and Brian Hughes' help I'm delighted to say we were
> able to sneak a test in just before winter makes its appearance. It was tee
> shirt weather, with high tide at the warmest time of day.
> 
> You may not be familiar with Shackleton, so here's a summary. She uses the
> main cylinder of an earlier project called Solo, which was to be a
> hydrobatic sub and therefore had a very slender (i.e. only 31" diameter)
> main hull. Solo lost her wings and tail but gained battery pods, a CT, a
> deck, etc. Shackleton herself has already been through several iterations,
> specifically of the MBTs. In the first iteration I made a big mistake - I
> concentrated my calculations on submerged stability, just assuming the MBTs
> would provide stability when surfaced. Nope! The second iteration used a
> raft MBT, which is far more stable than the streamlined hull-hugging
> initial version. That solved the surfaced stability issue. However, it had
> a new problem. The raft was composed of a bunch of small aluminum tanks,
> plumbed to valves on the CT just like a Kittredge sub. The problem was that
> the plumbing had do cover quite a distance and suffered from water
> blocking. This is the third iteration, and uses a raft of four MBTs but
> with mushroom valves rather than the K boat arrangement. Water blocking
> can't happen because mushroom valves go straight on the tanks and have no
> plumbing at all. I can already say that although it took me a while to
> arrive at, I'm a fan of the raft configuration implemented with mushroom
> valves. BTW the valves are controlled in pairs, so the pilot can open or
> shut the two forward valves or the two aft ones independently.
> 
> What worked well:
> - As mentioned, the raft MBT provided good stability.
> - The boat floated at the calculated waterline and in trim.
> - The vertical thrusters blow water through the deck grating. I was curious
> how much efficiency this would cost, but it appears a very acceptable
> compromise.
> - The four thrusters are jettisonable. They are held against the hull by a
> bolt, and they seat against electrical connectors that are insulated from
> the water by an O ring. I have a short-detection circuit to make sure those
> O rings aren't leaking. I used it, and found no leaks. Thruster controls
> worked great.
> - The boat uses a combination of trawl floats and steel ballast to adjust
> buoyancy, with no VBT. Today's test was with just one person aboard, and in
> salt water. In other words, the scenario that calls for max ballast. We
> turned out to be balanced with a tad less than the full complement of
> weights - the theoretical numbers turned out near perfect.
> - I love the fast submergence!
> 
> Needs work:
> - The thrusters are fine going forward but quite miserable in reverse. I
> think this is due to a combination of two factors. First, in reverse the
> prop wash hits the MBTs - I can't really do anything about that. Second,
> I'm using after market props that are supposedly faster than the stock
> Minnkotas. But I think they accomplish that by being biased for forward
> motion. I'll be switching back to the stock props.
> - Two of the mushroom valves don't seal 100%. I'll be putting in slightly
> thicker O rings to see if that stops it.
> - The hatch leaked, even though it didn't on past tests and didn't when I
> tested water-tightness with a vacuum two days ago. The hatch is bolted to
> its hinge, and washers on those bolts adjust the fit. This is just
> something to tinker with, but I know it can seal successfully.
> Unfortunately I have to remove the hatch each time the sub goes in and out,
> to fit under the garage door opening.
> 
> And now... let winter move in! The next step will be a nice spring day
> dialing in ballast configurations for one or two occupants.
> 
> Thanks,
> Alec