Re: [PSUBS-MAILIST] new to the list

["Cliff Redus" <dr_redus@devtex.net>]

> Cliff Redus wrote:
> >
> > Mike, for propulsion, I am using the drive train and impellor and nozzle
> > from a Sea Doo XP jet ski.  The screw is a three blade axial flow single
> > stage pump that is bolted in a frame in the aft of the boat.
>
> What I didn't see was the jet drive; all I saw was the four-bladed
> scimitar at the stern.  How much control will you get from those
> narrow blades?

It is hard to see but the blades are welded to a tube that is welded to the
end of the articulated nozzle, so that the entire fin assembly is
articulated.  Both the nozzle and the fins are introducing a radial turning
force. Incidently, the shape of the fins is based on one of the fasted fish
in sea, a blue fined tuna. (See MIT work on bionic tuna).

>
> > For yaw
> > control, this gives me +/- 26 degrees of rotation and +/- 8 degrees for
> > pitch control.
>
> Why, then, do you have the blades abaft the jet?

Could actually get by without fins at high speed, but at low speeds, the
fins will give added control.  Besides, it would look mighty strange with no
fins!

 with 20 HP dc
> > motor connected to 120 VDC controlled by a Curtise PMC model 1221C-7401
> > Transistor Motor Controller.  With a POT this enables me to vary the
speed
> > of the motor and jet pump from 0 to max rmp or even reverse the motor
though
> > in my case, I am not planning on doing this.  The speed range on this
motor
> > matches the rather high shaft rpms needed by the jet pump.
>
> What rpm does the pump expect?
0-5000 rpm nominal, 7200 rpm max.
>
> >  On the surface,
> > I am driving the jet ski impellor with a Rotax 787, two-stroke engine
that
> > puts up 110 hp.  I know that using a two-stroke engine is a bit
> > controversial for psubers but I could not find a marine diesel with the
> > power to weight ratio I was looking for.
>
> I'd not argue about it.  One uses what works!
>
> Have you asked the Coast Guard what they want you to change on
> the Rotax?  I recall getting some official flak when I asked
> about using a lawnmower motor to drive a generator.

Have not gone to Coast Guard yet.
>
> > I could not stand the weight  of a
> > marine diesel for this boat size. It would have caused me to increase
the
> > overall size of the boat which in turn would cause more drag.
>
> How much does the Rotax weigh?

With support structure and all parts of the engine, its comes in at 132 lbs.


>
> >  To address
> > the safety issue (gas fumes), I am connecting exhaust and intake
manifolds
> > directly to hull penetrations on either side of the sail and I am also
> > planning on using a carbon monoxide sensor that will shut in the engine
if
> > readings go abnormal.
>
> I'd given some thought to putting a gasoline engine in a separate
> pressure hull.  It's be expensive, and once I'd given it some *more*
> thought, I realized a big problem was that I'd not be able to
> get to the engine while in the water.

I came to much the same conclusion.
>
> > At normal speeds this combination of engine and motor
> > give a calculated 98 mile surface range and a 63 mile submerged range
using
> > 18 gals of fuel and a full charge on the batteries.  The batteries are
> > charged overnight with a BYCAN model BY-120/132/144-25A onboard battery
> > charger (for 120-144 volt battery packs).
>
> That's a good range.  Take photos of the first trip!
>
> By the way, your side view shows the sail with an angle
> forward.  What advantage do you gain?

Because I am using ASME PVHO-1-1997 rules for viewports, I have to go with
one of the standard shapes unless I want to spend a fortune getting a new
viewport designed certified. (something like an F-16 canopy shape would be
nice) Because the hemispherical viewport protrudes above the streamlined
shell, separation of flowlines occur at the aft portion of the pilot
viewport. Separated streamlines are bad news for drag. Down the road to
reduce the overall drag coefficient, I was considering an ambient pressure
streamlined acrylic cowling that would encapsulate the hemispherical
viewport and if you like fill in the dead space between the sail and the
viewport.  The forward facing sail lends itself better to this enhancement
down the road.
>
> I want to see this one operating.  It's beautiful.
>
>
>
> Mike

Thanks, I am looking forward to starting fabrication.

Cheers!