[PSUBS-MAILIST] Shackleton testing

[Alec Smyth via Personal_Submersibles]

Hi everyone,

Just a quick update on Shackleton test dives we made last week. Many
thanks to Brian Hughes, Dan Lance, Steve McQueen, and Mark Ragan, who all
drove big distances and set aside three days in the middle of the week.

An earlier trailering issue has thankfully been resolved. Make sure you
have sufficient tongue weight!!! The longitudinal location of the sub in my
case produces about 300 lbs of tongue weight per inch that you move the sub
forward, so it's absolutely key to locate the sub accurately. The earlier
problem was that the trailer went into harmonic oscillation and decided it
liked to travel next to the tow vehicle rather than behind it. Solution:
Increased tongue weight to 580 lbs, reinforced the tongue to deal with
that, and added a damper between trailer and tow vehicle. Here is the
damper:
https://www.campingworld.com/curt-manufacturing-curt-17200-sway-control-kit-91408.html?gclid=EAIaIQobChMIzZySh9vx5AIVD2yGCh1lOQXZEAQYAiABEgIZ3fD_BwE

I added buoyancy foam bolt-on flotation for operating in fresh water with a
crew of two, which is the maximum payload/minimum buoyancy scenario. It
worked perfectly, and is cheaper than syntactic foam. The sub happens to be
the right shape for a material that comes in sheets. In the pics, these are
the flat white slabs on the side of the MBTs. The material is R-3315,
described in this article:
https://sea-technology.com/feature-article-low-density-polyurethane-foam-for-subsea-buoyancy-systems

Diving with the mushroom valves is sure different, and decidedly easier. In
a K boat, you flood MBTs somewhat tentatively, intermittently opening and
closing one or the other valve to keep the boat level. I've abandoned that
practice in Shackleton, and just leave both MBT valves open until under.
That only takes seconds, so there's no concern about getting out of trim
because there isn't time to - she stays flat.

The sub dives so fast that flooding MBT puts her in vertical oscillation.
Lets say you dive in perfect trim, just a few pounds positive. The sub will
descend until the CT is 7 feet underwater, come up and break the surface,
then go down again but not as far, bob up again and break the surface, and
finally stay there. Initially we were looking to dial in the ballast and
this was a little confusing, because the first impression upon venting is
that the boat is heavy. However, once ballasted there is no need to bounce
up and down when you dive. If you add down thrust while flooding MBT, she
goes straight down.

The system of using trawl floats to adjust for different crew weights
worked beautifully. When changing crews, you just lift a trapdoor in the
deck and add or remove floats. They are located under the front half of the
deck, since that is above the passenger and thus aligned with the weight
variability you are adjusting for. I'll never use VBT again, this is
simpler and works really well.

Stability was also really good. Several people can walk around the deck,
and you can go to any edge of the deck without inducing much heel at all.
After diving for a while, if the crew wanted to switch positions we
surfaced, both got out on deck, and got back in again in reverse order.

The only thing that was fidgety, although it still did its job, was the
pressure compensation regulator. I have a differential pressure gauge in
the sub, which allows me to see how the compensation pressure compares to
ambient. I set it at +4psi but this sometimes (other times not) went to
zero at depth. On surfacing it seemed to have trouble venting and climbed
to +9. Cliff uses the same exact regulator with no problem, so I might just
have a dud. It is an industrial regulator, but I think I might trade it out
for a SCUBA 2nd stage because that would have a far larger vent valve.

A surfacing blow consumes about 300psi. That does not completely fill the
MBTs, I could blow far more, but it is sufficient to get out and walk
around. So a set of tanks is good for about 10 dives and I will plan on 8.

Shackleton has two battery pods with 6 batteries each. We dived all day on
one bank and it's charge indicator only went from 10 to 8 bars. So I'm not
sure how accurate or proportional that instrument is, but it said we had
only used about 10 percent of battery capacity in a full day.

At last, I've a compass that works and we were able to follow headings
submerged with no problem. It's on the deck, about a foot above the main
cylinder and two feet in front of the CT. You just look out the window to
read it. I tried running the thrusters hard but did not observe any effect
of their current on the compass. In Snoopy my compass would spin.

We tested the emergency release float. It worked fine, and the nice thing
is that the release can be stopped when the float reaches the surface, to
avoid trailing a super long line. But someone said there is a mechanism
that allows you to wind it back in from the sub, and that would be even
better!

Freeboard came out to design, 24 inches. Even trim.

We only went to 25 feet, and next up will be a depth test - most likely in
the spring.

Best,
Alec
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