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Prop Choice - 4/28/2012 4:56 PM   
Jackal1983


 

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Hi Guys,

Im really comfused in choosing a prop!!!

When you want a prop in a real boat you get a Prop pitch of say 15/19... And a prop pitch of 11/18


I have two model boat props a 6717 3 blader and a 7015 3 blader...
I want to drop a few pitches can somebody tell me what these numbers mean... are they just part numbers or do they mean something? Is there a graph somewhere that shows the pitch to the number.

I have a Makara Deep V hull with a Bonzi bz4 Zenoah in it... and i cant get it to come on song at all!!! It just doesnt want to rev... Ive changed the pipe, all carb settings are stock on the 257 carb..... So my thoery is to drop the prop pitch down a few beg and let the poor motor rev its arse off!!!

Jack



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RE: Prop Choice - 4/28/2012 5:10 PM   
Jackal1983


 

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Status: offline 		Ahh ive done a search and found some information

With Octura props, the X series (an X before the number) indicates a low lift prop. Props without the X are high lift props.

Ex.: X470 Octura prop
X= low lift prop.
4= pitch ratio
70= 70 mm diameter 

1667

Octura prop
lift prop
1.6 AR
67mm diameter
So: pitch divided by diameter= (AR) or pitch/67=1.6 or pitch=1.6 x 67= 107.2 mm diameter or 4,2" 

Taken from here!!!
http://www.rcprops.com/TechNotes/rcprop_tech_info.htm

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RE: Prop Choice - 4/28/2012 11:46 PM   
HendricX



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Status: offline 		You are totally wrong ! !

In a 6717 prop (metric-size) the 67 is diameter .. and the 17 is 1.7 pitch-ratio or ;

67 x 1.7 = 113,9mm total throw (moving forward) of the prop.

On the 7015 this is 70 x 1.5 = 105mm total throw.

So your engine will rev higher with the 7015.

Buy a Octura X470/3 (70 x 1.4 = 98mm total throw) and it will even reving higher.

Arithmetic on Imperial sized props is the same .. ,

a ABC 2714 is 2,7 Inch in diameter with 1.4 pitch-ratio .. or 68,58mm x 1,4 = 96,01mm total throw.

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RE: Prop Choice - 4/28/2012 11:51 PM   
Dan S



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Status: offline 		Jackal,

your 6717/3 has 67mm diameter, 1.7 pitch ratio

67 x 1.7 = 113.9mm of pitch or 4.48 inch of pitch.

your 7015/3 has 70mm Dia, 1.5 pitch ratio

105mm of pitch or 4.13inch of pitch.


Darn it, Hendrix beat me to it, I'm slow at typing. lol

Dan.

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RE: Prop Choice - 4/28/2012 11:53 PM   
Jackal1983


 

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Status: offline 		Yes the motor revs very slighly higher with the 7015 on... Only fractionally!!!

So after reading a few articles ive ordered a X470 3 bladed prop.... I have found a X470 2 blade prop so i might try that tomorrow if the wether is nice!!



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RE: Prop Choice - 4/28/2012 11:57 PM   
Jackal1983


 

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Status: offline 		That makes sence dan... Thats why its only reving fractionally higher with the 7015/3 on it!

I think the X470 will be an inprovement

I thought a BZ4 Zen would of turned a 7015/3 easily... I guess not!

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RE: Prop Choice - 4/29/2012 12:21 AM   
HendricX



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quote:

ORIGINAL: Jackal1983
so i might try that tomorrow if the weather is nice!!


If the weather on your side of the pond is as ugly as over here .. not a chance ... :-(

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RE: Prop Choice - 4/29/2012 2:15 AM   
Ron Olson



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Status: online 		If you really want to be confused, there are many versions of the 6717 props so where you get it can make a big difference! Not all props of the same size are made identically. There can be pitch changes anywhere along the path of the blade, more or less cupping or the blade shape itself.

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RE: Prop Choice - 4/29/2012 2:48 AM   
glennb2006


 

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quote:

ORIGINAL: Jackal1983

That makes sence dan... Thats why its only reving fractionally higher with the 7015/3 on it!

I think the X470 will be an inprovement

I thought a BZ4 Zen would of turned a 7015/3 easily... I guess not!



I run a few Makara's and with 26cc motors run a 7015/3 on all of them, I have yet to find a motor that won't turn one, obviously, the more power the motor has the faster it'll turn the prop, but overall I ifnd the 7015/3 hard to beat as a mono prop, very little prop im[act ont he handling of the hull, from my experience so far.

One thing that most likely is worth checking when running the 7015/3 is the strut or stinger position, I have had to raise the centreline of the drive to allow the engine to pull the 7015 properly, and on most of my Makara's I run with the centreline of the drive shaft 13mm up from the tip of the vee on the bottom, you can go a little higher if you like.

Start with this set up and the pipe length around 340mm and shroten from there, so long as there is nothing wrong with the motor then it should be able to spin that with ease.

Let us know how you get on though.

Glenn

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RE: Prop Choice - 4/29/2012 2:05 PM   
Jackal1983


 

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Status: offline 		Hi Glen,

Some good info there bud.... I'll try that next weekend!!

I'll have a look at the stinger position and let you know next weekend.

I surpose if less prop is in the water the more it will be able to turn it!!!


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RE: Prop Choice - 4/29/2012 4:36 PM   
glennb2006


 

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Status: offline 		Indeed. And it helps with the handling. Guess you too are washed out today?

Glenn

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RE: Prop Choice - 4/29/2012 10:11 PM   
Jackal1983


 

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Status: offline 		Yes just abit !!!!... Complete washout!!!

Im going to have to rework the back end of the Makara to get 13mm from the keel to the shaft centre!!..

I'll try this new prop next week then see if i can lift the stinger up... At the min the stinger sits level with the bottom.. so the shaft is around 7mm to the centre!

Where do take your boats bud??? Do you race??

Jack


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RE: Prop Choice - 4/30/2012 9:24 AM   
qdemon


 

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Status: offline 		Hi Jack
just out of interest what pipe are you running with the BZ4 ?, it sounds like the engines not coming on the pipe, a BZ4 should handle both the 6717 / 7016.

Bob.

no go the lake this weekend rain rain rain, monday still rain


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RE: Prop Choice - 4/30/2012 10:03 AM   
Jackal1983


 

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Status: offline 		HI Bob.
Ive been my pipe was my first choice. I changed from the bindi quite pipe that's the split able alloy lump to a prestwich pipe.
Doesnt seem to of made and difference except its a tad louder... Lol..
Maybe I need to reduce my pipe length from 13.5" but I'll play with prop heights.

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RE: Prop Choice - 5/1/2012 2:22 AM   
glennb2006


 

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quote:

ORIGINAL: Jackal1983

HI Bob.
Ive been my pipe was my first choice. I changed from the bindi quite pipe that's the split able alloy lump to a prestwich pipe.
Doesnt seem to of made and difference except its a tad louder... Lol..
Maybe I need to reduce my pipe length from 13.5'' but I'll play with prop heights.



I run at our local lake in Sunderland, the website linked here shows a map of where we are. http://www.herringtonmodelboatclub.tk/

We have a race series for some sport and fun around the buoys on the lake, nothing too serious though.

As to your symptoms, a pipe too short would cerainly not help, try and set it for an initial settign at 340mm from the flang face of the exhaust port to the fattest part of the pipe, generally a good starting point, and don't forget to chop off any extra header hiding inside the pipe.

Modding the hull to get the prop centreline higher should take two minutes once the strut / stinger is out the way, use a rough round file and file a slot up the transom, then slot the screw holes too.

Bolt it back up, set the height, shaft in, rev up and go.

Glenn

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RE: Prop Choice - 5/6/2012 8:31 PM   
Jackal1983


 

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Status: offline 		Hi Guys
Well tryed with an X460/2 prop today with stinger centre line set at 13mm and it seemed to be going alot better... engine was reving more..
Very pleased so far!! Cheers Guys!!


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