[PSUBS-MAILIST] Alec's test

Fri Apr 14 09:20:34 EDT 2017

Alec, thanks for posting the trip report on Shackleton.  I was interested
in the testing you did on your printed Kort nozzle.  From the testing
we did on the MK-101 variable pitch prop project, we found a pretty large
variation in performance of different props with and without the nozzle for
these MD-101 motors.  Just because you have a nozzle it does not guarantee
better thrust.  As example, if you look at test results below, the 4" pitch
open water prop that ships with the MK-101, the MKP-33 with out the nozzle
generated 82 lbs of bollard thrust but when installed in the nozzle, the
thrust drops off to 71 lbs.  This is not always the case.  Using the 5"
after market Kipawa 80/01 prop when tested without the nozzle, the thrust
was 80 lbs but with the nozzle it jumped to 90 lbs.  To me one of the big
issues seems to be the tip shape. To get good performance you have to
minimize leakage of pressure from the high pressure side of the blade to
the low pressure side around the tip.  This is why all props on thrusters
with nozzles have tips that are square off rather than rounded with a small
gap between the blade and the nozzle.  I don't know the prop you were using
but my guess is that it was an open water prop with rounded tip. Can you
send a picture from the stern showing the prop in your printed nozzle?

[image: Inline image 1]
[image: Inline image 2]

On Fri, Apr 14, 2017 at 7:41 AM, Alec Smyth via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Oh I'm not celebrating yet - the sub hasn't made any dives! I was just
> puttering around on the surface and only submerged in shallow water where
> there were still six inches of the CT showing when I reached the bottom. It
> might have been possible to dive, but I'd rather try it once the
> water-blocking issue in the plumbing is addressed.
>
> On Thu, Apr 13, 2017 at 11:24 PM, Alan James via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
>> Congratulations Alec,
>> How deep did you dive? Are you busy selecting a sound track for the video?
>> I am wondering if you were turning toward the tunnel thruster because
>> thrust can
>> push out to the side without the restraint of a kort nozzle!
>>    I have done a preliminary drawing for a solenoid operated ballast valve
>> based on the top hat design that Vance gave out in Islamorada. With it
>> being
>> electrically operated you could control it with a gyro sensor using a
>> board
>> that controls quad copters. That way at the flick of a switch you would
>> descend horizontally. (in theory).
>> Did you use the new lights?
>> Cheers Alan
>>
>>
>> ------------------------------
>> *From:* james cottrell via Personal_Submersibles <
>> personal_submersibles at psubs.org>
>> *To:* Personal Submersibles General Discussion <
>> personal_submersibles at psubs.org>
>> *Sent:* Friday, April 14, 2017 2:58 PM
>>
>> *Subject:* Re: [PSUBS-MAILIST] Alec's test
>>
>> That sounds great Alec! Congrats on a great build. I'm sure you'll iron
>> out the minor venting issue.
>>
>> Greg
>>
>> ------------------------------
>> *From:* Alec Smyth via Personal_Submersibles <
>> personal_submersibles at psubs.org>
>> *To:* Personal Submersibles General Discussion <
>> personal_submersibles at psubs.org>
>> *Sent:* Thursday, April 13, 2017 10:47 PM
>> *Subject:* Re: [PSUBS-MAILIST] Alec's test
>>
>> 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
>> <personal_submersibles at psubs.org>>
>> *To:* Personal Submersibles General Discussion <personal_submersibles at psubs.
>> org <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 thruster
>> in to a plumbing merchant or hydraulic repair shop & ask for something
>> compatible with a barbed hose fitting. Sometimes a metric option will
>> fit 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 <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 <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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