[PSUBS-MAILIST] Shackleton testing

Tue Oct 1 22:10:46 EDT 2019

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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