[PSUBS-MAILIST] Alec's test

Thu Apr 13 22:44:59 EDT 2017

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 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> 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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