Trolling Jet Motor?

[howbroker]

First Time Post - Looking for advice on the viability of a 12 volt "Prop-less trolling" motor.

My favorite bass pond gets pretty weedy in the summer, and I spend a lot of time stopping and pulling weeds (Lilly pad stems) off my 55 lb thrust Trolling Motor.

The Question - Is it viable to build a "prop-less trolling motor?" I have read many of the forums on Jet Drives, and understand the loss of power, poor handling issues at low speeds inherent with the jet drive.

Most of the posts are discussing ways to generate more power, more efficiency, more speed. I'm looking for some realistic ways to generate enough vector-able thrust, that I could avoid the weedy prop issue and the low draft issue.

The 55 lb trolling motor easily moves my 10 foot, 2 man "Bass Buddy" boat around my 10 acre pond in my quest for bass. Can a 12 volt pump generate enough power to move this light plastic boat? (100 lbs empty) Does anybody know if there is one commercially available? (I haven't been able to find one) Your thoughts and ideas would be welcome.

[charmc]

Hi, howbroker,

Welcome aboard.

A jet drive is, essentially, a shrouded prop. I seem to recall that there are some shrouded prop designs out there, some for trolling motors. Here's a guaranteed weedless prop: http://www.iboats.com/Minn_Kota_Weedless_Wedge_Prop_MKP_7/dm/category_id.238346--view_id.239625

The patented Weedless Wedge is the only 100% weedless prop in the history of fishing. And it delivers full power so there’s no need to carry an extra prop and a wrench. The design behind the Weedless Wedge is both simple and brilliant. The leading edge on each propeller blade is shaped with a swept-back edge that always meets at an angle of less than 45 degrees. “Wedges” weeds away from the hub — even at slow fishing speeds...even through a jungle.

Another reson for using an electric trolling motor is that they are designed for quiet operation, less chance of spooking the fish. Silent operation is not an attribute of most jet drives, at least those I've seen. :)

[redtech]

it's nice to have howbroker,
charmc is right on about noise and jet units but to add a little more jets and weeds don't get along either. small piece of debree plug the intake then no water to the impellers

[srimes]

shallow draft and unaffected by weeds: Paddle wheel. Not real quiet though.

[Rick Willoughby]

I expect lilly pads will just gum up the inlet on a jet.

This boat is reportedly quite immune to weeds:
http://www.streamdancer.com/
It uses auger type props. These avoid blades that trap weeds. There are amphibious vehicles based on the same concept; been around for a long time:
http://web.ics.purdue.edu/~warnerd/index_files/Page1421.htm

One way to beat the weeds is to do what is done in the swamps. Avoid water propulsion and use air. Problem with this is you need a large prop to do anything useful. Something like 2ft diameter on a 10ft boat would get you moving but efficiency only 40%.

The electric RC stuff you can get for peanuts (or maybe a little more) these days are very powerful. This motor is bigger than you need for power but is the sort of size needed to swing a big prop unless you set up gearing - why bother though:
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5144&Product_Name=HXT_63-54-A_250Kv_Brushless_Outrunner_(Eq._52-20)

Hobbycity have some large CF blades but I have not looked at how they mount. Large RC copter blades would be close to ideal. A couple of kg of thrust is all you need:
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6603&Product_Name=TIG_325mm_Carbon_Fiber_Z-Weave_

There are Bolly props made for large models but these get expensive:
http://www.bolly.com.au/models/glasstwo.html
The 24X8 would do something useful at reasonable efficiency. Need to mesh to guard it.

The fundamentals of a water thruster work against your little pump idea being very efficient. If you could set it up to avoid the inlet fouling you have to have quite large power to generate usable thrust. As a first approximation the ideal power as a function of thrust can be determined as:
Power = (4/pi/9/rho)^0.5 x Thrust^(3/2)/D in Watts

You will require a thrust of 20N (say 4.5lbf) to do something useful. Rho is 1000kg/Cu.m. D has to be in metres so for a 1" nozzle say 0.025m. Under these conditions the ideal power is 42W. You could double this by the time you account for plumbing and pump losses. A 6" pump would need to spin at 800rpm to do the job. Something off-the-shelf like this would be adequate:
http://www.boatshop.com.au/prod19.htm
You would need to nozzle it somewhat to get the best result but it is the sort of size required. Anything smaller would be literally pissing into the wind. Efficiency would be similar to the air prop.

Rick W

[kistinie]

Does a manufacturer sells pump jet pods or pump jet propeller ?
,,,,,,pump propeller to use the good name,,,,

This for 5 to 10 Kw ?

Pump jet - pump propellers
http://zone.sousmarins.free.fr/zone%20sous-marins%20helices.htm
http://forummarine.forumactif.com/russie-union-sovietique-f4/pompe-helice-t325.htm
http://forummarine.forumactif.com/france-f1/question-sur-nos-sna-t4089-15.htm

these are supposed to be very efficient at high speed, but induce a drag at low speed
the stator is above propeller or after.

[apex1]

Does a manufacturer sells pump jet pods or pump jet propeller ?
This for 5 to 10 Kw ?

Pump jet
http://zone.sousmarins.free.fr/zone%20sous-marins%20helices.htm

As usual Francois, you do´nt know anything...............:p
There is no pod or prop, "Pump Jet" is a totally different world.
And only one manufacturer worldwide.

http://www.schottel.de/deu/r_produkte/produkte.htm

[kistinie]

Always a pleasure to ear your sarcasm !
At least you give a good informations, it is already a positive thing

French submariner call the dual or triple prop shielded system in submarine "pump jet" or "pompe helice'
I do not know why they use this name if it is not the good one.

So what is the name of this shield proppeller with many prop inside ?

[apex1]

Ducted Prop or Props
Rudderpropeller if it can be turned to at least 40° each side
helice gouvernal in your mothers tongue
was a pleasure

[kistinie]

Ok, good to know

So even with 3 propeller and a startrek design including water injection in the ducting, name is prop or ducted prop

No very romantic for such a secret technology :-(

this picture is a rudimentary pump used in industry for water
called "propeller pump"

the other link , a commercial boat pod using submarine technology, gain is supposed to be 10% (on a normal pod i guess)

http://www.meretmarine.com/article.cfm?id=103345

[mudman]

Go-devil.

Make your own out of a 5 hp engine. You should see what we get through with a homemade 6.5. Easy to make, fuel efficient. Very noisy.