ultra-low rpm prop.

[SolomonGrundy]

Hi all,
I've posted this Q to the folks at Michigan Wheel... I thought I'd give everyone a chance to put in their 2 cents worth.
The application is a 20' LWL aluminum disp. hull, multi chined, double ended vessel. Powered by a person who we hope shall be able to deliver between 1/6 & 1/3 hp. I estimate that through gearing we will be able to deliver between 100 and 200 rpm to the shaft (5/8") quite consistantly.
The hull was designed with the notion that we would be using a 2 bladed prop with a 32" radius.
Ideally, once I have the shape of the prop, I'll lay them up from carbon fiber and vaccume bag them...So maybe I won't hear back from MW...
Any and all help would be greatly appreciated. Should someone actually take the time to (please forgive my naievete) "do the numbers" and come up with a workable design, not only would we be extreemly grateful, but that person would go on my "A" list...cards on Christmas, birthdays and Bastille day.

[SolomonGrundy]

http://boatdesign.net/forums/attachm...5&d=1128467175
to see he hull...

[SolomonGrundy]

Wow, not all at once...

[FAST FRED]

At these low speeds and with such limited HP you should contemplate a prop similar to an aircraft prop.

The surface area can be very smal as the prop loading will be minimal.

To carve a wooden prop visit the EAA site and get the info there.

I would contemplate a SINGLE bladed prop , yes with tiny counterweight , as that would have best thrust with lowest induced drag,will work IF you can handle the REQ diameter.

FAST FRED

[SolomonGrundy]

Fred,
Thanks for for your input. The designer brought up a few interesting ideas that I haven't totally discounted yet. Although highly unconventional (not much about this boat isn't), he proposed having a prop that comes out of the water for half its revolution. I saw some examples of this, but I'm not sold yet...also he proposed a similar device using counter rotating props on either a shaft in a shaft, or something like an egg beater gear...
I'm not sure if I want to experiment with these as I don't know how much, if any, efficiency/speed is gained by this, but so far nothing is off the table.

Thanks again, SG

[cyclops]

Something to do to find the speed and prop size you can handle. Get any working about -10 speeds bike - see if you can thread 2 pieces of shafting to fit each end of the axle. 2 simple pillow bearings, near the axle ends. Make 1 shaft long enough, 5' to 10' to go thru a simple little type of boat to support you while you pedal different gear ratios and normal props. Set 2 floating milk jugs 1/4 mile apart and stopwatch yourself. Cheap, accurate and good training.---------------I'll hold the watch!

[cyclops]

Something to do to find the speed and prop size you can handle. Get any working about -10 speeds bike - see if you can thread 2 pieces of shafting to fit each end of the axle. 2 simple pillow bearings, near the axle ends. Make 1 shaft long enough, 5' to 10' to go thru a simple little type of boat to support you while you pedal different gear ratios and normal props. Set 2 floating milk jugs 1/4 mile apart and stopwatch yourself. Cheap, accurate and good training.---------------I'll hold the watch.-------------Not awake , the axle does not turn . Need to think up something better.------------- I will check with a couple of bike shops, if we can simply remove all the spokes and make a solid coupling from the hub to the shaft and pull this idea off.

[SolomonGrundy]

Well they sure blew me off...

[yokebutt]

Have you spoken to the people at AeroVironment? They might have some ideas.

Yoke.

[JPC]

I've only got a short minute, so couldn't do better than the two links below, but you might find that they lead to some information.

I used to race (rowing) in the San Francisco area; one well known figure in the open-water circuit is Gordie Nash who developed a pedal-powered boat (catamaran using two Van Dusen racing-shell hulls). Gordie and the boat were very competitive against the traditional shells.

I realize that you have a different specific design in mind, but Gordie may have tinkered through some of the same mechanical/propeller issues that you are looking to solve.

It appears that Dick Lyons -who also rowed with us in the Bay- is commercializing Gordie's design up in BC Canada -perhaps under the "Gazelle" name, but I couldn't find a direct reference in my quick search.

One observation is that part of Gordie's success in the rough waters of the Bay arose from his ability to keep his propulsion unit in the water rather than fighting the varying surface height of rough water with oars. This might suggest that the surface prop proposal is not good for a boat that does not create it's own flat water behind the transom (unless you expect to be on glassy water) - not sure: I don't know much about the requirements of that prop design.



http://www.ihpva.org/pipermail/hpv-b...q2/005591.html

http://snorlax.lampi.org/mike/cruise2005.html

[Alixander Beck]

i'm interested in hearing what gear ratios you will be running this prop on.