Unique Propeller Application

[Ottfather]

I'm in a unique situation in that I'm looking for a propeller not for a boat, but for a passive device that will rest on a river floor. It can essentially be thought of as an underwater wind turbine, and is commonly known as hydrokinetic power. In sum, high speed river currents will turn this propeller which will power a small generator. There will be no gearbox as the generator is designed to be spun at low RPM's.

There are a few problems with choosing the right propeller for the job. Mainly, the RPM's I'll be running at are much less than a typical boat, somewhere around 200 - 300 RPM hopefully. At these RPM the generator will be at around 500 Watts or about 0.66 HP, so very low power. The main goal of the propeller is to turn as efficiently and rapidly as possible from river currents traveling at around 2.5 meters per second, or about 6 MPH. The diameter needs to be close to 15". Thus, I think light weight will be key, and perhaps a carbon-fiber blade would work well.

Due to the extreme costs of getting a propeller custom-designed (from what I have found) I'm really hoping to find an off-the-shelf propeller that will work well. The problem is I'm having a really hard time finding anything with specs even close to this. Is there a certain "type" of propeller that would be best suited for this? Any cheap custom designers? Should I be looking at low or high pitch? Any recommendations would be extremely helpful.

Let me recap the data:

Anchored propeller powered by river currents at 6 MPH
15" diameter
200 - 300+ RPM (want to maximize)
Attached to small generator rated at 0.5 - 1 HP

 

[Silvertip]

Re: Unique Propeller Application

Whether you need a high pitch or low pitch propeller requires the same set of considerations as selecting one for a boat. Too much pitch you lose and too little you also lose. Somewhere in the middle is an optimum pitch. It would appear to me that a four or five blade prop would be needed and even then the effectiveness of a standard marine propeller in this application may not be optimal. I would think a turbine-like device would be far more effective and that you could make yourself if you are so inclined. A three or four stage turbine operating inside a cone-shaped housing with a six MPH current could be quite effective. Marine propellers would seem to have the wrong architecture for this application. Look at the old windmills that used to pump water on farms. Those single stage mills worked pretty well with only slight winds. A six MPH current channeled by a tapered housing could develop a fair amount of power.

 

[rbh]

Re: Unique Propeller Application

Yes I would certainly look at going with a turbine style blade as well, 16-20 blades, stainless steel construction,
the turbines construction plans can probably be found in google somewhere.
good luck

 

[propper_advice]

Re: Unique Propeller Application

I work with a company that has provided props for many special applications from use in spas to power generating waterways. Since my products are not available on iboats, I cannot provide specific info. However, if you want to send me a message I can direct you to some possible solutions.

 

[DBreskin]

Re: Unique Propeller Application

Anchored propeller powered by river currents at 6 MPH
15" diameter
200 - 300+ RPM (want to maximize)
Attached to small generator rated at 0.5 - 1 HP

Your current and RPM requirements work out to a propeller pitch of 13.6 inches:

250RPM=15000 revolutions per Hour
15000RPH/2.5MPH=6000 revolutions per mile
6000 revolutions per mile / 5280 feet per mile = 0.88 revolutions per foot
0.88 revolutions per foot = 1.14 feet per revolution = 13.6 inch pitch.

I'm not aware of standard 15" diameter propellers with pitches below 15 inches. In your case, a longer pitch means the propeller will turn slower, since the propeller is being driven by the water rather than vice-versa. These calculations do not consider drag/load from the generator.

Boat propellers are engineered to be efficient when driving, rather than being driven, so you may end up with a very inefficient system. I agree with the previous posters that you should consider a turbine-type design, even though it may mean you have to have it custom built.

 

[FAC]

Re: Unique Propeller Application

you might want to look into using model airplane propellers they are fairly inexpensive and are available in many different diameters and pitches it would probably be fairly easy to make a multi bladed unit out of a few propellers just another idea to consider

 

[Silvertip]

Re: Unique Propeller Application

Again, model airplane propellers are not designed for this application for the same reason marine props are not efficient in this application. You need lots of blade area for slow speed power.

 

[FAC]

Re: Unique Propeller Application

i agree that an off the shelf airplane propeller would not have enough blade surface area but if you combined 3 or 4 or more 2 bladed propellers it could be efficient enough for this application it would not be 100% efficient but it would be fairly inexpensive and allow you to experiment with different diameters and pitches and blade numbers easily

 

[Silvertip]

Re: Unique Propeller Application

Here are three sources of info on water turbines. The vertical axis style is one that can be easily built at home. Too bad the propeller version shown does not have a better view of the propeller. However, I've seen some of those props and they have extremely large blade area and are uniformly shaped somewhat like an elephant ear pontoon prop.

http://www.exmork.com/submersible-turbine-generator.htm

http://www.absak.com/catalog/index.php/cPath/33_89_90

http://www.ehow.com/how_5256700_bui...ce=yahoo&utm_medium=ssp&utm_campaign=yssp_art

Let us know how this project unfolds.

 

[ArcadianStar]

Re: Unique Propeller Application

I have helped students from Long Beach Polly High with their solar race boats. We had really good luck with the Duffy Electric Boat PLASTIC prop. The price was cheap and after thinning it some, it worked very well for their race boats!

You can buy them from Duffy direct. I'd say they are around 13 X 13, but don't hold me to it!

 

[woosterken]

Re: Unique Propeller Application

how about the blade off an old house box fan? they are plastic and move a lot of air
pick one up at a yard sale or good will

woosterken

 

[45Auto]

Re: Unique Propeller Application

The most efficient low speed airfoil (or propellor) will use long, lightweight, high aspect ratio blades. There's a reason gliders have long skinny wings and the windmill farms you see on the hilltops have long, skinny blades.

I've worked with several companies that are trying to install the "underwater windmills" in the Mississippi river. Most of the designs look very similar to the pictures in this article:

http://www.popularmechanics.com/science/earth/4213223.html

Some of them are using ducts around the blades, like these:

http://www.fastcompany.com/blog/kit-eaton/technomix/hydroelectric-power-goes-greener-river-turbine

I don't think you'll be able to come even close to what you're looking for with a boat propellor. Your blades have to absorb less than 1 HP (doesn't matter whether they're driving or driven, the blades don't know the difference). The wimpiest boat propellor has a much higher power loading and is designed to be efficient at much higher speeds than 300 RPM.

 

[lowkee]

Re: Unique Propeller Application

Found you a nice one, only $18, too! Looks to be stainless steel

http://www.nelsonappliance.com/Metal Fan Blades for Lakewood model P25 Fan.html

There is always the old fashioned method:

 

[204Angler]

Re: Unique Propeller Application

I am interested in seeing your project unfold. After all the recommendations for what type of turbine set-up to use vs. a boat propeller....I will not add to that since there is ample advice there already. The only thing I will recommend is a different bearing. I was an aircraft mechanic for sometime and when we would play around and experiment with wind generation, we would use "Air bearings". Bearings that have no mechanical friction and do not require any type of lubrication. They are filled with compressed air, or nitrogen. The power loss through these bearings is almost exactly null.
I do a lot of experimentation with different pitches, materials, diameters, aspect ratios, bearings, gearings with different velocities of varying media.
Let me know ifyou have any questions about construction or if you have new ideas. I love hearing about people doing this like this.
My wife and I are going to be building a house on a piece of land that has room for a water way. I am going to set up (try to) something I have been trying to work on. I am going to dig a pond with a graded "stream" situated in a semi-circle around the pond. The water will be pumped from the pond via a permanent siphon and water will be deposited on the "up-side" of the graded stream. I will attempt to build a type of hydroelectric dam in the stream. Should be an interesting project.
Sorry for the tangent. Let me know!

 

[lckstckn2smknbrls]

Re: Unique Propeller Application

Found you a nice one, only $18, too! Looks to be stainless steel

http://www.nelsonappliance.com/Metal Fan Blades for Lakewood model P25 Fan.html

There is always the old fashioned method:

IIRC in war torn Bosnia They were making generators out of car parts. The front spindles, wheels with paddles welded on, V-belts and alternators.

 

[45Auto]

Re: Unique Propeller Application

I am going to dig a pond with a graded "stream" situated in a semi-circle around the pond. The water will be pumped from the pond via a permanent siphon and water will be deposited on the "up-side" of the graded stream. I will attempt to build a type of hydroelectric dam in the stream.

Either I don't understand what you're trying to say with this, or you don't understand how a siphon works .....

 

[elkhunter338]

Re: Unique Propeller Application

It you are set on trying a boat prop try a 4 blade propulse.
14.5" size with a pitch adj. between 15-21.
I run one of these props on my boat and it works just fine.

 

[turbodude51]

Re: Unique Propeller Application

If this is fresh water, why can't you use the wind turbines that go on house roofs to ventilate the attic? the good ones are rust proof with ball bearings and spin with no resistance. I think that would be easier to adapt.
Rick