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modified21
02-21-2012, 02:03 AM
I was just wondering if the total pitch (pitch x diameter) of the prop affected the temps and speed if they are relatively similar, kind of like gear ratios. Ex. A 642 prop has a 2.640 total pitch and a 448 has a 2.660 total pitch. Or is all this more in line with a tire like height and width (acceleration and traction). Sorry if this confuses but it the best I could break my thoughts down

Boaterguy
02-21-2012, 07:50 AM
I think I understand what you mean
the issue is that if you took an x642 vs an x447, the x642 will have more pitch, but the x447 may be faster on a particular hull.
this is because the x642 has less blade area (ie. it is smaller), and will slip more if it is pushing a big hull.

modified21
02-21-2012, 01:13 PM
hmmmm, i believe i understand. So the prop diameter is really the determining factor in choosing a prop, and pitch is like a fine tuning point??? I only ask because i would like to begin collecting an arsenal of props and was trying to figure out a general starting point without having to purchasing 50 different props.

Chilli
02-21-2012, 01:42 PM
It's really a total package. Prop pitch, diameter and blade shape. An ABC prop with the same numbers as an Octura can give you dramatically different results.

The best thing you can do is post your set up here and people will give you some recommendations. Be sure to post whether you want a prop for sport boating, racing or top speed. Be carefull what you read!! Some people may tell you a certain props works for them, but they just wanted to see how fast they can get their boats for short runs. Run the same prop for 5 minutes and :flame42:.

I've been into this hobby for four years and am just starting to understand props.

Boaterguy
02-21-2012, 04:15 PM
hmmmm, i believe i understand. So the prop diameter is really the determining factor in choosing a prop, and pitch is like a fine tuning point??? I only ask because i would like to begin collecting an arsenal of props and was trying to figure out a general starting point without having to purchasing 50 different props.
not exactly, you have to take both factors in, and well, I don't understand much of it if any.
what nauti said is correct, it is not all down to numbers.

modified21
02-22-2012, 03:32 AM
It's really a total package. Prop pitch, diameter and blade shape. An ABC prop with the same numbers as an Octura can give you dramatically different results.

The best thing you can do is post your set up here and people will give you some recommendations. Be sure to post whether you want a prop for sport boating, racing or top speed. Be carefull what you read!! Some people may tell you a certain props works for them, but they just wanted to see how fast they can get their boats for short runs. Run the same prop for 5 minutes and :flame42:.

I've been into this hobby for four years and am just starting to understand props.

Thanks, I was hoping there would be some magical number or theory that I could wrap my hand around but from what it seems nothing beats past experience and some good ole trial and error.

modified21
02-22-2012, 03:42 AM
not exactly, you have to take both factors in, and well, I don't understand much of it if any.
what nauti said is correct, it is not all down to numbers.

Well thanks for the replies, I almost thought I would get no responses as my question was kind of way out there, my three builds are almost complete and one is getting ready to start so I need to get some props ready. Between reading every tidbit of info in every post I just never found a reason as to why props were suggested almost seemed no reason to the madness, I see everyone just throwing out suggestions for props with no relative explanation as to why.

srislash
02-22-2012, 09:16 AM
Thanks, I was hoping there would be some magical number or theory that I could wrap my hand around but from what it seems nothing beats past experience and some good ole trial and error.You pretty much got it.We have water conditions,whether you run the hull loose or wet,how much amperage you can pull.Alot O' playin.That's the challenge/fun.

srislash
02-22-2012, 09:23 AM
Well thanks for the replies, I almost thought I would get no responses as my question was kind of way out there, my three builds are almost complete and one is getting ready to start so I need to get some props ready. Between reading every tidbit of info in every post I just never found a reason as to why props were suggested almost seemed no reason to the madness, I see everyone just throwing out suggestions for props with no relative explanation as to why.
For the most part you pick a diameter based on the hull size and motor power.Then you can play with pitch and such to get speed or run time.IE-a large diameter prop with a strong motor will spin the boat(roll it over or torque it over) so one may run a smaller prop with more pitch to get the same speed.
Sorry I didn't chime in earlier but I've been busy.Thought somebody else might have as it is a good question for a "new to FE" to search for in the future.

modified21
02-22-2012, 07:12 PM
For the most part you pick a diameter based on the hull size and motor power.Then you can play with pitch and such to get speed or run time.IE-a large diameter prop with a strong motor will spin the boat(roll it over or torque it over) so one may run a smaller prop with more pitch to get the same speed.
Sorry I didn't chime in earlier but I've been busy.Thought somebody else might have as it is a good question for a "new to FE" to search for in the future.

This is why I brought up the idea of total pitch in relation to speed and heat build up. This is what I was thinking. If I take at x448 prop and start to get heat issues I could move to a x642 prop which has the same total pitch (practically) but is smaller in diameter and get theoretically the same speed then I move up to the next size prop to achieve greater speed with less heat. Is this thinking along the correct line or am i hopelessly roaming the forest with no bread crumbs, and thanks for the response everything helps.
There isn't any clubs or even other boat in my whole part of the states so I have no one to ask and my dad who raced nitros 20 years ago doesn't have a clue about FE (he races scratch built sailboats now <---slow and boring) so sorry if I am beating this question to death

dana
02-22-2012, 09:58 PM
my understanding is that,higher kv motors have less torque then lower kv motors. so theres the starting point for prop selection. an octura x6 series has more pitch, and therfore requires a motor with more torque. an octura x4 series have less pitch and do better with higher kv. if you use a prop with a higher pitch on a motor with high kv, the motor is working to hard and probably not getting the rpms it should be loaded. so personally i start with motor kv, and select pitch first. then i consider the size of the boat. certainly an x447 on a 26' boat is just silly…. thats just how i choose. if i want to go faster, i never go ridiculous with the prop size, i just change the motor/batteries accordingly.

Make-a-Wake
02-22-2012, 10:09 PM
Also, small hulls tend to do better with small diameter to decrease torque roll. Some motors, like Neu's for instance, like diameter as opposed to pitch.

What size hulls will you be running and i'll try to give you what i think would be a good 10 prop "arsenal"

lohring
02-29-2012, 06:20 PM
Once you have an example of what power a propeller absorbs, there are ways to calculate what changes in the propeller will do. The power absorbed is proportional to the diameter to the fifth power, the rpm to the third power, and directly to the blade area and the pitch. That's why tiny changes in diameter, like rounding the tips, make big changes in the current draw. Adding pitch makes much less difference.

Lohring Miller