[PSUBS-MAILIST] Shackleton testing

Wed Oct 2 06:18:58 EDT 2019

Alec,

Great report.  Sounds like really succesful dives.
Do you have any pics?   Interested to see the pressure regulator.

Regards
James

On Wed, 2 Oct 2019 at 03:11, Alan via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Alex, Cliff,
> thanks for the report Alex, I hadn't thought about the oscillation from
> flooding the ballasts too quickly.
> As for the compensating regulator, Cliff I am about to try it out on my
> thruster on an inflatable boat. I am having an air over oil system. Just
> bought
> a 18 cuft pony bottle for it.
> There is silicone oil in the thruster housing & in the line leading to the
> compensating
> regulator. So very little air is required to compensate, & if oil leaks
> out it is
> replaced by air & indicated by the oil height in the line.
> Alex, as for the pressure differential in the regulator; I am not sure
> what operating
> range you chose for that regulator. Did you go for the lowest range?
> I think they have a piston which could stick a bit in that low 4 psi
> range, hence your
> zero pressure. The relieving part of the regulator is set by the size of
> its spring.
> You could put a weaker spring in if you want the pressure relief on
> ascending
> to be closer to your set pressure, however you run the risk of it free
> flowing.
> In commercial spring pressurised compensators they get a variance in
> pressure
> larger than what you are experiencing, but this is over time due to the
> spring
> extending as the oil level goes down.
> Alan
>
>
>
> On 2/10/2019, at 6:31 AM, Cliff Redus via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Alex, great report on mods to Shackleton.  It sounds like the mods you
> made to both the trailer and MBT system worked. The discussion on the fast
> acting MBT mushroom vent valves was interesting, particularly the part
> about the vertical oscillation.  My guess is another way to null out the
> oscillation would be to open the MBT vents for a specific amount of time so
> that you were shooting for flooding 80% of the MBT volume, close the MBT
> for a short time then open them again to finish the flood.  I bet if you
> experimented with this you would find a set of time constants that would
> generate a fairly fast but smooth flood without oscillation.  As you say,
> it is not a big deal as you can null out with vertical thrusters.
>
> On the air pressure compensation issue.  On the R300, I have gone over to
> the dark side and switch to oil compensation on all my thrusters.  Yes air
> compensation with the pressure reducing regulator has worked fine for years
> but at the Flathead Lake Expedition, I had issues with the the aft
> thrusters partially flooding.  It could have been that the pressure
> reducing regulator needed servicing.  The primary reason I switched is that
> I just don't like using up my HP air with this task.  For shallow dives it
> is not big deal but for deep dives to 200-300 ft air consumption is
> significant.  I am using WD-40 for the pressure compensation and the small
> plastic accorfdian bottles you sent me for expansion.  I put a strobe light
> on the thrusters to measure rpm of the Minn-Kota 101s with both air and oil
> compensation.  There is about a 5% reduction in shaft speed under no load
> conditions out of the water.  I did not detect a significant change in
> current again under no load conditions.  Next step is to take the R300 to a
> local lake to test the "dark side" pressure compensation for the thrusters.
>
> Back to your test.  How was the underwater maneuverability and the view
> through that magnificent bow viewport?
>
> Cliff
>
> On Tuesday, October 1, 2019, 11:29:37 AM CDT, Alec Smyth via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>
> 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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