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Which Propellor? - 8/31/2012 11:13 PM   
leaflite


 

Posts: 7
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Last Login: 9/5/2012
From: , UNITED KINGDOM
Status: offline 		Hi
I posted a while back about a Frog 349 marine diesel engine that I had been given. Ive since bought a hull on ebay and am now wondering what size prop will be needed.
The hull is 57cm long, and requires a prop of the submerged type. The existing propshaft is m4 threaded at the prop end so I will need something that just screws on, not a dog drive?

The engine specs according to the manual are: 3.47cc/0.21 cu. in., 0.32bhp at 13500rpm, 29 oz-in of torque at 9000rpm

What propellor would suit? I dont know much about RC boats, and any advice I can find on prop size for a given engine cc is usually refering to more powerful nitro engines, so Im not sure whether that advice will apply to my engine, so im clueless

Thanks

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RE: Which Propellor? - 9/2/2012 7:19 PM   
yellow-bird


 

Posts: 103
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Joined: 11/12/2010
Last Login: 3/3/2013
From: Farmington Hills, MI, USA
Status: offline 		Hi Leaflite

I posted before but don't see my reply now.

You motor spec is similar to the "700" size brushed electric motors that used to be popular before brushless took over.

Graupner do a range of 4mm carbon-plastic diameter screw-on props which you should be able to find inexpensively.

I suggest starting with something like their 36mm diameter x 50mm pitch prop or maybe the 37.5 x 52. This should get you in the right ball-park - these are typical for brushed motors or .15 nitro motors in the 24-26" monohull range. They also do a 3-blade 36 x 50 prop which you could experiment with since you have a relatively low-revving motor.

- yellow-bird


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RE: Which Propellor? - 9/2/2012 9:04 PM   
leaflite


 

Posts: 7
Score: 100
Joined: 8/6/2010
Last Login: 9/5/2012
From: , UNITED KINGDOM
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quote:

ORIGINAL: yellow-bird

Hi Leaflite

I posted before but don't see my reply now.

You motor spec is similar to the "700" size brushed electric motors that used to be popular before brushless took over.

Graupner do a range of 4mm carbon-plastic diameter screw-on props which you should be able to find inexpensively.

I suggest starting with something like their 36mm diameter x 50mm pitch prop or maybe the 37.5 x 52. This should get you in the right ball-park - these are typical for brushed motors or .15 nitro motors in the 24-26" monohull range. They also do a 3-blade 36 x 50 prop which you could experiment with since you have a relatively low-revving motor.

- yellow-bird




Great!

Thanks for the reply

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RE: Which Propellor? - 9/2/2012 10:40 PM   
leaflite


 

Posts: 7
Score: 100
Joined: 8/6/2010
Last Login: 9/5/2012
From: , UNITED KINGDOM
Status: offline 		Just had a look and it seems that I can get a graupner 2 blade S series, 2 blade K series, or another 2 blade (2327/2318/2305), or a 3 blade (2299) in the sizes you mentioned

Which would suit best?

Thanks

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RE: Which Propellor? - 9/3/2012 8:33 PM   
yellow-bird


 

Posts: 103
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Joined: 11/12/2010
Last Login: 3/3/2013
From: Farmington Hills, MI, USA
Status: offline 		Hi Leaflite

Looking at the specs, you would probably be better off with a higher pitch propellor as your engine is relatively slow-revving.

Therefore I would suggest the 2327.36 S-series 36mm prop, which has a pitch of 57mm and would suit a high torque motor.

The alternative in this size is the 2318.36 which is also 36mm diameter but has a pitch of 50mm. This equates to a "lower gear" than the 57mm pitch and better suits a higher revving engine.

The 2299.36 is the three blade version of the 36mm prop, also with a 50mm pitch. The extra blade area gives better acceleration from a standing start, but again may suit a higher rpm motor than the one you have.

I don't think the K-series will fit your prop shaft - I think they are for 3/16" (5mm) shafts.

-yellow-bird


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