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 Determining the prop specs for your need??? 
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Joined: Wed Sep 16, 2015 11:50 am
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Post Determining the prop specs for your need???
So I have been doing some research and and trying to figure out what each component of a prop's specs does to increase its performance. The parts are diameter, pitch, # of blades and if the prop is cupped.

Pitch has been the easiest. It represents the distance in inches the prop will travel in one full revolution. Obviously the larger pitch the greater distance you will travel and faster. (All else equal)

Cup was another that I understood fairly easily too. It throws more water in shallow situations helping to propel the boat. Kind of falls in line with pitch.

What I'm having difficulty understanding is how the larger diameter blade and number of blades helps. Does more prop in the water push more water and help carry a load better? More blades is supposedly faster?

Input appreciated


Fri Aug 11, 2017 4:21 pm
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Joined: Mon Dec 31, 2012 11:07 pm
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Location: West Monroe, LA
Post Re: Determining the prop specs for your need???
Blade surface area affects how much water a propeller can interact with. Ignore engine power for a moment. A propeller with a total blade surface area of 50 square inches at 100 rpms will create a specific amount of thrust. It will directly touch a certain amount of water. A different prop with 75 square inches at the same pitch, same amount of cup, and same rake at 100 rpms directly touches more water, which creates more thrust. Make sense?

Now, add back in engine power (the ability of the engine to turn a propeller a specific rpm). The balance of pitch and cup to get the performance of characteristics you want to take advantage of the engine power ideally for you is affected by blade size. For instance, you can't have 75 square inches of blade in contact with the water and still use the same cup and pitch as one with 50 square inches in contact. 3 blades, 2 blades, 4 blades all have different amounts of metal fighting the water at the same time, as do 2 blades with different blade profiles. Or 3 blades. Etc. Still tracking?

Running a different blade profile, but the same surface area in contact with the water can also affect pitch and cup. They shed water or mud differently, and one may benefit from more cup, or pitch, or both, etc.

Vague enough of an explanation?

Basically, more blades or larger blades can help in certain circumstances, and hurt in others. Decide which performance factors matter most, and go from there. You want it to do better in the weeds? Mud? Holeshot or top end? Etc. All those things, plus others, factor in to why we choose a 2 blade, 3 blade, more cup, more pitch, or wish for something else entirely.

#CFFITR
#TheGhostBoat
#whoneedsphysicsihaveamudmotor


Fri Aug 11, 2017 5:09 pm
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Joined: Tue Jan 13, 2009 6:42 pm
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Post Re: Determining the prop specs for your need???
Throw in tip curl to really muddle things up.


Fri Sep 01, 2017 6:46 pm
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Joined: Mon Dec 31, 2012 11:07 pm
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Location: West Monroe, LA
Post Re: Determining the prop specs for your need???
Lol, was ignoring that and double cup. Figured why go that far

#CFFITR
#TheGhostBoat
#whoneedsphysicsihaveamudmotor


Fri Sep 01, 2017 7:41 pm
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