[PSUBS-MAILIST] Alec's test

Fri Apr 14 10:38:41 EDT 2017

Alec,The picture looks good, man that must be stable when fully surfaced!   You could be right about the water getting in the tubes, but you say water spits out with the air, that says to me the air is making it out.  I think what is happening is the raft tanks have solved the problem you had when they are full of air but when you release the air it is as if they don't exist and the sub returns to normal.  Also the platform is quite wide exacerbating the imbalance.   I think you will need to arrange it so you can add and release air in four quadrants.  Then she will be a dream!  Love that shallow draft!Extending the down spouts will  help for sure, but you may have to slow down the air feed to let it balance out.  My down spouts are about 14 inches long and solved my problem completely.  I would still like 4 quadrant control though. 
When I tested Gamma the other day I found myself 10 feet under water on a 30 degree nose down and 15 degrees  list hanging on so I didn't slide off the seat.  I am a test and adjust guy, but because I have long down spouts, I surfaced with ease and the sub self corrected.  The hydraulic tank assembly is very heavy hanging out the front corner.  Some well placed boulders off shore corrected that.
How do you find the control response with the motors pointing strait back and being so far back?  Hank

    On Friday, April 14, 2017 7:37 AM, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Hi Hank,
Good points. We might be calling two different things "vents." First, the issue with the tubing on the top of the tanks that releases the air for diving... If air were all that were in those when submerging, I agree there should not be a problem if they ran "downhill" a little due to listing. However, these are small tanks and the tubes in question are only 1/2" Swagelok. I think what's going on is that the water sloshing in the tanks will occasionally reach the entrance to those tubes and get sucked in along with the air, so you end up with a water block if that water goes downhill. At the top of ball valve that all these little tubes feed into, it's nearly all air coming out while flooding tanks but it does spit out water in small quantities. 
Second, the openings at the bottom of the tanks. I already have downspouts on them to prevent burping. They are only 5" long, but again because the tanks are small it would take a large angle of heel to burp past them and they did seem to prevent burping just fine. However, there was one thing I was unhappy with in this area. When blowing the tanks, I'm used to stopping the blow as soon as bubbles come out the bottom of the tanks. In this case, the bubbles are appearing prematurely because some tanks get to empty while others are still blowing down. I can reach the normal flotation line by keeping the blow going, but it feels wasteful to be dumping air out of the already-empty tank to let the others finish. Maybe next time out I'll just temporarily extend the downspouts by putting short lengths of hose on them. D'you think that would help? A more sophisticated approach might be to take some video from underneath and analyze the order in which the tanks are emptying, then put orifices on their air supplies to even things out. But that's surely a refinement for later.
I agree the ideal situation would be to have valving that separated the MBT into quarters, so I could control either fore-aft or port-starboard independently. Currently I'm set up fore-aft and have no way to add or remove buoyancy specifically to port or starboard. My logic in doing so was that the boat is symmetrical side to side, but that longitudinal trim was more likely to be thrown off by differences in the weight of the crew (up forward) or if diving solo by my moving between sitting up in the CT or crawling forward. When I re-plumb the tanks, however, I might actually change it to port and starboard. I have two ball valves to work with on the CT, and going to four would be a much bigger job than just re-routing tubing. It'll also be much more convenient space-wise to plumb all the tanks on one side to the ball valve on that same side. I'll just think of them as saddle tanks, which is pretty much what the raft arrangement is anyway - a "squashed" set of saddle tanks up high.
I'm afraid I didn't end up taking enough photos to update the project page, or any video. Here is a downsized photo attached on which you might be able to make out the tubing above the tanks and the downspouts beneath. I'm not sure what the size limitation on attachments is, so if it doesn't make it through please advise and I'll reduce it further.

Thanks,
Alec

On Fri, Apr 14, 2017 at 5:44 AM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Hi Alec,Congratulations !!  your issues are pretty minor in the grand scheme of things.  The problem with the venting is suspicious to me.  If the vent tubes do not have water in them, they should still vent air, even if they are below the water line because the weight of the sub is creating pressure inside the tank witch will force the air down hill so to speak.  I was not there to see it of coarse, so I could be out to lunch.  From what you describe, changing the lines may not do it, I think you will need individual valves, not per tank but per side.  I had a similar problem with Gamma, but in reverse.  When I surfaced the sub would list to one  side badly because I have a common vent for the front and back.  Ideally you want front and back and side to side.  I corrected this by putting extension tubes on the bottom of the ballast tank vents, this forces the water level to self balance because one tank will  not vent air out the bottom until the sub is level.It sounds to me like you have a similar situation. If you have the ability to control venting from side to side, you will also avoid the problem I had, and I suspect may still show up.  Your big tall CT could create this effect while transitioning.

Hank

    On Thursday, April 13, 2017 8:45 PM, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs. org> wrote:

 Hi Greg,
Well here's how it went - much better but there's one more issue to resolve. 
The change to a raft configuration for the MBTs has solved the surfaced stability issue. It was great, I could walk around to any edge of the deck without excessive list. The longitudinal trim was slightly down by the stern when empty, and trimmed out to perfectly level when a person was lying in the front half of the boat (stability was calculated for the boat with crew). She floats in water only just over waist deep, 38 inches, and the freeboard is 24 inches. The thrusters and their controls worked beautifully, and the "tank drive" is really, really intuitive. 
After launching I drove around on the surface a bit. I didn't get a measurement of speed but would say while slower than a K350 she's decidedly faster than Snoopy. I tested a prototype kort nozzle by mounting it on one of the stern thrusters only and then giving both thrusters equal throttle, to see which way the boat tracked. Surprise, the un-shrouded original prop was more efficient because the boat would turn toward the side with the kort. So I'm just going to put on standard prop guards, at least for now.
Part of the surface running I did lying down and looking through the bow dome. The view is ridiculously good! From the CT it wasn't bad either, and I was surprised how the flat domes made objects appear closer, something I didn't recall from the flat bow dome in Snoopy. In this one, the leading edge of the deck as seen through the CT viewports seemed only a foot away. The dome is something else entirely, and optically seemed to have the opposite effect of making things appear further away, but maybe that was just in contrast to the CT viewports I'd been looking though moments before.
And so here is the new problem. The raft MBT consists of a collection of aluminum tanks, each of which has SS tubing coming out the top and gathering at a manifold, which is piped to the ball valves on the CT. As some of the tanks are off on the edges of the raft, some of the tubing runs side to side at an angle (up to 90 degrees) to the centerline. When you start flooding MBT, invariably one side will begin to fill slightly faster than the other. The side that is flooding faster will be lower in the water, and the effect of this list on the opposite side is that the tube connecting tanks to their manifold is now sloping downhill instead of up. This blocks the high side from letting out air, which exacerbates the initial list. It's really obvious when you see it, I should have thought of this effect. But luckily the solution is obvious too. There are two ways to fix it; remotely actuated valves right on the tanks, or new manifolds that are high enough to keep all tubing going uphill at reasonable angles of list. My initial impression is that the simpler of the two methods is to modify the plumbing. 

Best,
Alec

On Thu, Apr 13, 2017 at 10:10 PM, james cottrell via Personal_Submersibles <personal_submersibles at psubs. org> wrote:

Did anyone hear how Alec's test went today?

      From: Alan via Personal_Submersibles <personal_submersibles at psubs. org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs. org> 
 Sent: Thursday, April 13, 2017 9:34 PM
 Subject: Re: [PSUBS-MAILIST] Oil Compensator

Jon,an easy solution is to take the thruster, or that section of the thrusterin to a plumbing merchant or hydraulic repair shop & ask for something compatible with a barbed hose fitting. Sometimes a metric option willfit in an imperial thread, & so they may know of not so obvious solutions.Alan

Sent from my iPad
On 14/04/2017, at 12:53 PM, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs. org> wrote:

Hi Hank,
No, I don't have the shaft, I purchased just the lower head.  A 36 inch shaft is $28 but like you said, I really only need a few inches of it so don't really want to purchase it that way.
Jon 

    On Thursday, April 13, 2017 8:27 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs. org> wrote:

 Jon, Do you have the shaft that used to screw into the motor?  if so, you can cut it down to a couple inches long and put a waterline compression fitting on that.   Then reduce from the compression pipe thread.  Or you can thread the inside of that stub shaft with a pipe tap and reduce from that, providing it is the heave fibreglass shaft.Hank 

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