A Single Blade Propeller

[tom kane]

Food for efficiency and other skeptics . A boat propeller operation in shallow water and mud, stones, soon makes a prop look very sad. It is like a slasher bashing every thing in it`s path.
A single blade screw,auger (like a post hole borer) is the answer and has been used on ice tractors in quarries and many industrial applications and does not suffer so much damage.
The image shows a Bob Drive modified for some tough work and cheap to build or you can use a trimmable shaft or Pivotal drive. Yes it has been tried and is hard to control in deep mud because it wants to go streight ahead.

you could probably use a conventional post hole borer already built,and if it is a two stroke ignition changed to run in reverse.

[hoytedow]

It is yet another use for the Archimedes screw.
http://en.wikipedia.org/wiki/Archimedes'_screw

[FMS]

Interesting idea Tom. I see how this works in mud or sand like a screw drive tank or RTV concept on a smaller scale.

But in water, what diminished return does the blade area longer than a traditional blade offer with the column of water already accelerated?
Would the pitch be constant from end to end of the screw or progressive?

[gonzo]

It has been tried and found to be inefficient. The first powerboat used one like that, made of planks. When some planks came loose and fell off, the speed increased.

[Boat Design Net Moderator]

Off-topic and unfriendly remarks have now been removed from this thread. Please, let's keep discussions on-topic and respectful to fellow forum members. Thanks.

[PAR]

Gonzo is correct in that the screw type of drive was tried first, but it was quickly superseded by what is now a more conventional prop.

Having seen and worked on augers used in farming applications, I can say they don't fair any better then a conventional prop, but they do have so much more blade area, that they can adsorb more damage then a regular prop, before they no longer are effective. This doesn't mean they're better suited for the task, just heftier.

For these types of shallow, dirty water applications a slower turning prop, massively built with "raker" properties, would likely be the better option. Something designed to bash into things and still come up all standing. If spun slow enough you can "torque" your way through mud and other debris. Personally, I think you just have to live with a certain amount of damage potential in some situations. Having removable/replaceable blades or back up props, are just the "cost of doing business" in some areas and one I'm all too familiar with. I drive props into the sand and mud all the time. I'm forever banging them straight, welding on new material and changing blades or wheels. It's just life in the shoals. Maybe titanium coated, carbide tipped . . .

[nukisen]

Hi Tom!
The idea about the rudder thing seems oki for me.
About the skrew prop we do have a fysical problem as the resistant of the big surface on a propeller like this makes the water to spinn along the prop and decreases the effect. Actually I have tried this on a model. It works but the effect loss is to high for acceptance.
Another idea is to make two screws working as a screw compressor works. Then you kill the option for water to twist along the screw. But if this is effective in water I dont know?

[nukisen]

Tom!
Also the rudder helps to stop the water from twist around the propeller screw.
So if you make the screw shorter and exchange the rudder axel to a flatbar this will help stop the water from the twisting issue.

[tom kane]

I did not have a choice on the type of screw I used,it was cast alloy a reject from a Ilb butter packing machine and was progressive.The fun did not last long as more speed was wanted.
I would not expect such a drive to be fast but it did do a fine job of what I expected from it and would be great for those who have a constant use for it.

Water and mud worked best which is what we wanted.The image shows the much altered boat with a e93a Ford motor with closed water system which used to get too hot and gave us some fun.The rocker of the boat gave a nose up ride and a shallower draught slow speed.

[nukisen]

Woaha!
This is what I call a modelprototype.
Of course it works!

But I think the option from the picture below helps increase the power.
As the water no longer are able to twist when leaving the spiral prop the centrifugal power are no longer able to throw away the water from the propeller. I am not sure but my mind says it does work better.

[FAST FRED]

One advantage to a conventional prop with a single blade is it could be a CPP version and the larger diameter of the hub would be offset by the larger working diameter.

FF

[tom kane]

Another method to limit the damage to a propeller was a ring around the blades, a mini kort nozzle on a trimmable shaft drive but you would expect to go slower but not necessarily less thrust.
The ring helped to automatically lift the drive as you hit sand bars and mud.
The ring was easily detached for repairs and was not permently fixed.