[PSUBS-MAILIST] Alec's test

Fri Apr 14 11:56:16 EDT 2017

James running the MK-101 at higher than design voltage could work. I am not
a propeller expert but there here a complex interaction between pitch, rpm,
impellor diameter, efficiency and slippage that makes it hard to guess on
the effect of changing any one parameter.  In the testing my students did,
the rpm actually increased when they put the MKP-33 prop in the nozzle from
1486 to 1590 and the thrust dropped off.  As to running the MK 101 at a
higher voltage, the nominal voltage for this trolling motor is 36V .  You
would have to abandon the Minn-Kota motor controller to do this.  There are
many off the shelf motor controllers that would work but MK has a lot of
nice protection features built into theirs for incidents such as a fowled
props.  The best way to look at this would be with some controlled test
where you logged the thrust, motor speed and current and varied one
parameters at a time.

Lots of fun R&D to do and not enough time!

Cliff

On Fri, Apr 14, 2017 at 9:37 AM, james cottrell via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Hi Alec,
>
> Haven't tested this but here are my thoughts and I hope Cliff will respond-
>
> It might be that a prop that is fitted closely inside a tube loses some
> rpm because it has no "slip". Its being forced to work harder. If the rpm
> drops drops below the "sweet" speed where the prop is most effective then
> overall efficiency goes down.
>
> One solution may be to overdrive the voltage. For instance, a 12 volt
> trolling motor can be run at 18 volts without damage as long as the amp
> rating is not exceeded. If the amp rating is say 30, then you run the motor
> at 18 v but limit the rpm when your amps reach 30.
>
> The result is more rpm with less heat. If this were applied to a trolling
> motor inside of a kort nozzle then maybe the rpm loss would be brought back
> up were it should be and efficiency would return.
>
> Cliff- any thoughts on this?
>
> Greg
> ------------------------------
> *From:* Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.
> org>
> *To:* Personal Submersibles General Discussion <
> personal_submersibles at psubs.org>
> *Sent:* Friday, April 14, 2017 10:04 AM
> *Subject:* Re: [PSUBS-MAILIST] Alec's test
>
> Hi Cliff,
>
> It's the standard MK prop, turned on the lathe to fit the nozzle. Since
> the prop would be working a little harder to push water through a nozzle, I
> reduced the diameter a little in an effort to keep the current draw more or
> less standard. It also gives a better edge than the pointed tip would have.
> But even so, the results in practice were not good. Please let me know if
> the attached picture doesn't go through.
>
>
> Thanks,
>
> Alec
>
> On Fri, Apr 14, 2017 at 9:20 AM, Cliff Redus via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> 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 <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.o
> rg <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.o
> rg <personal_submersibles at psubs.org>>
> *To:* Personal Submersibles General Discussion <personal_submersibles at psubs.o
> rg <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.o
> rg <personal_submersibles at psubs.org>>
> *To:* Personal Submersibles General Discussion <personal_submersibles at psubs.o
> rg <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.o rg <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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