[PSUBS-MAILIST] Shackleton test report

Wed Dec 5 17:07:35 EST 2018

Hi Alan,

The valves have a spring so they default to closed if un-powered, but I'm
driving both the open and close directions pneumatically. The slight leaks
in two of them should be a matter of fidgeting with the cap and its O-ring.
It's a conical seat, and I'll experiment with different O ring thicknesses,
but if not I'll just make new caps. Prior to this, I had tested the valves
by inverting the tank (off the sub) and filling with water. However, I
hadn't filled them to the top due to mounting holes, so they had more
pressure now.

As a next step I'm investigating ways to further increase buoyancy. The
present range allows one or two person operation in salt water, but I need
some extra buoyancy for two people in fresh water. The great thing is the
test gave me a confirmed reference point rather than a spreadsheet of
estimates.  At some point I may go back to playing with things like the PLC
or a joystick, but frankly the controls are the best part of the boat the
way they are now, as they'd still work if I dunked them in the ocean. I
really want to get the basics to battle tank grade like that before I turn
my attention to the nice-to-haves.

Love your research with the thrusters!!!

Best,
Alec

On Tue, Dec 4, 2018 at 3:20 PM Alan via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Alec,
> WOW, a lot of work has gone in to that. The seat retraction mechanism etc
> & Some innovations I haven't seen before, like the power connections for
> the
> dropping of the thrusters & the "twist & release" mechanism for the buoy
> release.
> I was intending to have my ballast valves opening down rather than up & are
> wondering if wave motion is compressing the air in your ballast tank &
> opening
> the valve against it's spring pressure. You said it was leaking a bit of
> air.
> Great attention to detail; it is looking good.
> I guess the next step is a manipulator? And what about a flight controller
> like
> David has ordered!
> Cheers Alan
>
>
> On 5/12/2018, at 8:15 AM, Alec Smyth via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Hi friends,
>
> I've updated the project page with new photos.
>
> http://www.psubs.org/projects/1234567810/shackleton/
>
> Best,
> Alec
>
> On Mon, Dec 3, 2018 at 11:02 PM Alan via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
>> Thanks for that great report Alec.
>> Glad it went well.
>> Alan
>>
>> > On 4/12/2018, at 1:29 PM, 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, an!
>>  d 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
>> > <47258859_10217781304468113_8654460041761390592_o.jpg>
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