Centrifugal pump for boat propulsion 2

[StreamDancer]

Designing an electric powered personal fishing catamaran.
We started with two trolling motors for propulsion and differential thrust steering but the trolling motors must draft at least 15". The craft drafts only 5" and we would prefer to have propulsion wherever the boat will go.

We have recently embedded the trolling motors vertically in the hulls and attached flat-backed impellers to the shafts. We then covered the impellers flush with the hulls, exposing 90 degrees of the 360 degree rotation to the water below and also cut a 2" hole in the cover to let water into the center.

The boat actually moves forward and reverse, but very slowly. We need someone with sump pump savvy to help us improve efficiency. We know that our straight vanes are not as efficient as spiral shaped vanes, but that would prohibit reverse.

Any guidance would be appreciated,

John Zimmerlee
Marietta GA
770-565-4420

 

[MikeHalloran]

You might as well turn the motor axes horizontal, remove all shrouding and mount the impellers like sidewheels at the waterline. You'll need fenders to keep the splashing down. This will also work with smooth discs. I think Tesla figured that one out.

I have seen small outboards equipped with centrifugal pumps instead of gearboxes and propellers. They're not a marvel of efficiency, but your rig is probably much worse; the volute is an important part of a centrifugal pump.



Mike Halloran
Pembroke Pines, FL, USA

 

[StreamDancer]

Mike and anyone interested,

I'm not smart enough to argue any points, but I've seen something similar at

http://www.vortapowersystems.com

and believe that the theory, though not as efficient as propellers, should work for this craft. I just need some help with the volute design and some estimate of how much less efficient straight vanes are compared to spiraled.

StreamDancer

 

[MikeHalloran]

Karassik's "Pump Handbook" (McGraw-Hill) may be helpful. You may also find information in most any "Mechanical Engineers Handbook" you can borrow.



Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

Here is the disc type pump mentioned in MikeHallorand's post. You might contact them and see if the idea of using a disc is feasible.
You also might put a suction through the hull and discharge to the the rear using a disc for a the pump.

http://www.discflo.com/literature.htm

 

[Warpspeed]

One difficulty with the "Tesla" disc type pump in this application, might be fouling with weed and debris.

It would likely need a very efficient suction screen, which may also block fairly readily.

 

[berkshire]

Have you looked at electric bilge pumps?
There is a trade off between output and current consumpion, however you may find a compromise in the medium sized pumps. with say a 2" discharge.
B.E.

 

[StreamDancer]

In lieu of trolling motors, I looked at bilge pumps.
Since reverse is not possible and speed control is non-existant, I would have to use 12 pumps - one of each of 3 speeds in forward and reverse on both sides. the expense at $40 each along with the mounting nightmares and additional weight became overwhelming. Even so, the proplusion was not enough.

StreamDancer

 

[waross]

The comercial water jet propulsion installations do not try to reverse the pump for reverse travel. They use a diverter on the water discharge. The principle is similar to the reverse thrust diverters on a jet engine.
yours

 

[StreamDancer]

StreamDancer

This project was commended in the 2005 Intl Concept Boat Competition for its introduction of foot control to a personal fishing craft. Each foot has control for forward/reverse and speeds for each trolling motor . . . creating differential steering. Adding the mechanical reverse thrust would complicate the foot switch control.

The craft needs to be controlled in reverse speed and direction as aptly as in forward.

StreamDancer

 

[waross]

Try a smaller diameter propellor in a tunnel. Tunnel drives work well in shallow draft river boats. I was told by a builder-operator that even if the tunnel is partly above the water line, the prop will flush the air out.
yours

 

[berkshire]

StreamDancer (Marine/Ocean)
How about going in a different direction. Leave the motors vertically mounted and place a Voith Schneider propellor on the end of each. You would not need the steering function for your use. you could use your differential steering via motor speed. The site I have linked here is for a model not a full sized one.

http://members.surfeu.at/fprossegger/english/vsp-function.html

B.E.

 

[StreamDancer]

I tried the tunnel approach.
Formed a tri-hull with kayak-like hull down the center, tunnels on each side, and sponsons just outside the tunnels. Utilized trolling motors with 10" props in raised tunnels at mid-point in craft. The props cavitated profusely, so I lowered the tunnels. Stil cavitated until I got them so low that the tunnels were no longer needed. The original objection was to get the propulsion up high enough that the boat would be under power wherever the boat could float.

The Voith Schneider props looked interesting, but I can't find any one producing them. Every site talks about design and prototype.

I just can't believe that moore attention hasn't been spent on a shallow water propulsion system. The only one that seems to work is Vorta Power Systems. That appears to be nothing more than a sump pump with lateral discharge.
If it works for them, it should work for us!

StreamDancer

 

[zeusfaber]

Don't know if you can buy them as small as you'd want for your application (and they add a bit to your draft), but Voiths have been mainstream technology for decades.

Manufacturer at

http://www.voithturbo.de

A.

 

[MikeHalloran]

The trick to using Tesla's pump in a boat and keeping it resistant to fouling is to have just _one_ disk, projecting from each side, not in any kind of housing at all, just like a sidewheeler with no blades. It needs a close- fitting (but noncontacting) 'stripper' blade to get the water to leave the disk, and a fender to keep the water out of the boat.

Try spinning a tin-can lid with a hand powered drill and lowering it into a tray of water. You'll be amazed at the thrust, and the mess, it produces.



Mike Halloran
Pembroke Pines, FL, USA

 

[StreamDancer]

Mike,

The Tesla disc pump may be the answer. I emailed them for help this morning. I'm not sure what you mean by a stripper blade and wonder about the fender. If this disc churns up the water and/or splashes alot, the fish will swim for their life and the purpose will be defeated.

I am hoping for a cost effective quiet efficient system.
If that were possible, someone else would have come up with it years ago!

Stream Dancer

 

[Warpspeed]

I cannot help feeling that the old steam driven riverboats with single or twin paddle wheels, solved most of these problems a very long time ago.

 

[StreamDancer]

Success! . . . well moderate success.

Using a trolling motor (on each hull) turned vertically with 5" dia impeller (8 blades, each 1.5" wide), I was able to get the boat to move forward and reverse. Performance speed was only about half of what regular trolling motor props would do.

The good news is the boat only drafts about 5" and the propulsion system works wherever the boat will go.

I first had the impellers and the discharge area covered with a plate. A 2" round hole was cut just above the center of the impeller. Exit ramps (forward & aft) were exposed just beyond the discharge area. Performance was marginal.

I soon cut the cover off of the discharge area so that the entire forward/reverse ramp was exposed along with about 3/4" of the blades. That made an improvement, but the inlet hole was still getting clogged with weeds and such.

Then I open the area between the hole and the ramp on the cover. To my surprise, improvement again.

I'm now spreading the width of my exit ramps to get a little more cross-sectional area to push against.

I really need a pump guy to look at the design. An experienced pump person could probably tell me where I can improve without doing any calculations.

Stream Dancer

 

[btrueblood]

So, post a picture. Hard to "see" what you're talking about without it.