Author Topic: Propeller choice  (Read 2005 times)

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Calimero

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Propeller choice
« on: March 28, 2014, 06:22:45 »

I'm currently designing a barge for my springer tug. Looks like displacement will be around 25kg/55lb once ballasted with water.

I'm starting to think that my 4-blade 40mm brass prop might be a little on the short side. Though it would probably be more realistic ...

Anyways I was hence flipping through Raboesch's catalog.

I'm currently using a Raboesch Type 147 4-Blade 40mm prop. This one:



Diameter is 40m, pitch is 41mm (ratio 1.025).
Suggested use is: After 1940, used in ships with more power and similar speeds such as: Tugboats and pushing boats Fisher ships Work ships Cargo ships motor yachts.

Works great with my 800kv/6V setup but it might be a little too fast. Especially when pushing a barge I would probably need more thrust at lower speed.

A few pages further in catalog, I saw the type 174 4-blade props.




Suggested use is: These 4 blade propellers with large blade surface have great propulsion capacity at low revs. The props have been used in: Police boats Pilot boats and Torpedo boats Tender boats Frigates Patrol boats.

Pitch of a #174 40mm prop is 36.5mm (ratio 0.91).

This prop obviously has much more blade surface which I assume would result in more thrust.

Would such a prop (at constant diameter) give me more thrust at the expense of theoretical speed - as pitch is down ?

I'm somehow doubting as suggested applications (pilot boats, torpedo boats) are faster boats.

Last but not least there's also a 5-blade prop similar to the #147 4-blade one I'm currently using.




Pitch is 41mm for a 40mm dia prop, just like the 4-blade version. Same pitch, same diameter but more surface because one more blade ?

 :o

I can easily fit a 45mm prop instead of the 40mm one. Might even be able to push it to 50mm but I'd like to know which way to go.

Footski

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Re: Propeller choice
« Reply #1 on: March 28, 2014, 07:01:48 »
Personally, I would put the 40mm prop on and see how it goes. You can always replace it if you feel it needs it.
Barry

Calimero

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Re: Propeller choice
« Reply #2 on: March 28, 2014, 07:40:32 »
Yep. 40mm 4-blade prop works great and is enough for regular push jobs (as in recovering FEs).

And I'll push the barge -whenever it will be completed- with that prop before I try and get another one. Although they aren't very expensive, I don't want "useless" props laying around. Especially if this means switching to a slower motor.

But I willing to learn some of the theory beforehand.  :)

CGAux26

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Re: Propeller choice
« Reply #3 on: March 28, 2014, 13:10:35 »
My standard-built Springer has a speed 600 motor running on 6 volts, turning a 40 MM Dumas 3 blade prop.  It handily tows my 48 x 12" 55 lb barge.  I prefer pushing the barge from astern, or on the hip. 
Dave