[PSUBS-MAILIST] Shackleton test report

[Alec Smyth via Personal_Submersibles]

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
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