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Propping suggestions please.

Old 07-09-2010, 02:08 PM
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01VIPER27
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Default Propping suggestions please.

Hello gentlemen,
I bought the 6717 4BLR for the cool factor and thinking that the gearbox would make it easier for the engine to turn them over. I have yet to pass the 30 MPH range. The total weight of the boat is 24 lbs wet.

I have the engine below coupled to MHZ m-1570T (1:33) gearbox in a 64” Bonzi Fountain.
V3 M6: Combined 10 HP @ consistent full load @ full throttle @ high 17,000 RPM (AS TESTED to the gearbox)
*WT644 Big Bore Carburetor
*Lowered Intake Timing
*Raised Exhaust Timing
*High Hat Exhaust Porting
*High Compression
*Lightened Piston 21g
*Relieved Piston
*Copper Coated Base Gasket
Read more: http://www.rcuniverse.com/forum/m_92...#ixzz0tCuwhwpQ

My question;
I may be over-proped at 6717 4BLR on the V3 so I will be trimming it down to 65mm to test and then further cut it down to a minimum of 63mm so the engine can unload more. Failing this I will probably go to a 6517 or 6518 3 CR blade set or should I even consider a 6520 2 CR blade set?

I have been advised to use a wb gearbox 1 (1:1) with a 7017 3 CR blade set but I really do not want to buy another gearbox to operate in a lower RPM range. My thought on this is that it would load up the engine just as much where I am currently at. What are your opinions?
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Old 07-09-2010, 02:59 PM
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Scott Schneider
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Default RE: Propping suggestions please.

IMO ... bigger diameter props with less pitch will be Far more efficient in moving a hull of that size and weight.
Old 07-09-2010, 03:11 PM
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Default RE: Propping suggestions please.

Would that not load up the engine more and in turn make the boat go slower? I can have that boat push off from standing still no problem and have it pinned, to plane but I know it will not go any faster than 30 MPH. Hence, I really believe I need to go to a smaller diameter props to releive the engine. Please enlighten me.
Old 07-09-2010, 03:48 PM
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martno1fan
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Default RE: Propping suggestions please.

Why not go with a pair of 6717/3 props? same diam less blade so much easier to spin.Or go with 2 blade props and try a set of 275 ,good all round props.
Mart
Old 07-09-2010, 04:01 PM
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Default RE: Propping suggestions please.

just put a pair of 280's or 275's on it and see what it does? cheap to see some results. or you could try some very inexpensive 70MM plastic props too.
Old 07-09-2010, 04:17 PM
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Default RE: Propping suggestions please.

"Why not go with a pair of 6717/3 props? same diam less blade so much easier to spin.Or go with 2 blade props and try a set of 275 ,good all round props.
Mart"

just put a pair of 280's or 275's on it and see what it does? cheap to see some results. or you could try some very inexpensive 70MM plastic props too"

These I understand the reasoning.
Old 07-09-2010, 05:25 PM
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Default RE: Propping suggestions please.

Bigger the diameter more AREA is getting moved by the prop, Greater pitch is speed of water leaving the blade.
If props you have are spinning good rpm but not holding onto the water ... diameter too small or pitch too steep or BOTH.
Going to more diameter but less pitch loads up engine less than smaller and more pitch .... Think paddle wheel
Old 07-09-2010, 10:51 PM
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Justaddwata
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Default RE: Propping suggestions please.

I would just reduce the size and blade of the props you have. Do it a little at a time and be sure you get all blades the same size (and balanced). I have removed leading edge on several large props with a few boats in order to get the rpm up to a point that is more usable.

Keep in mind that an overdriven gearbox (like the 1.33:1 MHZ) will never spin a prop easier - it instead load up the motor more)
Old 07-10-2010, 07:25 AM
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brodjack
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Default RE: Propping suggestions please.

The FE guys run smaller props on big boats at higher revs and it works for them.
Old 07-10-2010, 07:43 AM
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Default RE: Propping suggestions please.

I would see if you can get a set of 7015/2 CR, no experience with twins or gearboxes but they are easy props to turn, bigger blades than the 67's, cost less and low lift. [8D]
Old 07-10-2010, 09:28 AM
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Default RE: Propping suggestions please.


ORIGINAL: Justaddwata

I would just reduce the size and blade of the props you have. Do it a little at a time and be sure you get all blades the same size (and balanced). I have removed leading edge on several large props with a few boats in order to get the rpm up to a point that is more usable.

Keep in mind that an overdriven gearbox (like the 1.33:1 MHZ) will never spin a prop easier - it instead load up the motor more)
Hi Matt,
Is this the same reason why I do not see a lot of twin drives going faster than 30 to 35 MPH with the same set up because the power plant should really be pushing out more HP and RPM unless they are proped down to a 2 or 3 blade set up with smaller pitch - unless of course the power plant is a turbine engine that can put out the RPM then most definitely it would not be a problem. Am I right in this assumption? Would I also be right in assuming that if I had bought a wd gearbox 1 would had been given me a better result?

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