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what size prop should i use

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Old 09-02-2012, 06:03 AM
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thebossman
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Default what size prop should i use

hello all..i am building a 30in long 15in wide with a 40 motor...airboat..what sise prop should i use...one more question..if i put the fuel tank under the motor will it have enough vac to run the fuel to the motor..thanks for the help rick
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Old 09-03-2012, 12:25 AM
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Altered1
 
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Default RE: what size prop should i use

The same rules for fuel tank placement as in planes....  You can probably get away with the tank a few inches below the carb, but it just makes one less thing to worry about if the tank is inline with the carb. (I've seen guys with a 6 inch drop to the tank, and they have no probs... but others do....)

For the prop - again, as a starting point,  go with a prop recommended for the engine in a plane, and start from there.  You are probably going to need to try a few different ones, going up or down an inch or two, and in and out in pitch will make a marked difference, and each boat is different.  Get a few different ones and see what works for your particular boat. 
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Old 09-03-2012, 06:28 AM
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1QwkSport2.5r
 
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Default RE: what size prop should i use

Put the fuel tank behind the engine using the tank rule. Center of tank lining up with the spraybar in the carburetor. Otherwise you will need a regulator to have reliable operation. Prop sizes, 9x6, 9x7, 9x8, 10x4, 10x5, 10x6 are good sizes. I run a 9x7 on a .46 myself.
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