quick prop question

[bwells]

I'm still trying to figure the prop stuff out. An Octura X642 has a final pitch of 2.64 and a Graupner 2317.48 has the same final pitch. Is the multiplier of 1.4 verses 1.6 not a consideration as much as the diameter? Diameter seems to be the king as long as the motor can spin it! Thanks

[sailr]

If you think it's OK because the motor will spin it, you will probably burn up your motor and/or speed controller.

The formula is like this:

an Octura 642 = 1.6 x 42mm = pitch, or 67.2mm Diameter 42mm, Pitch 67.2mm, 1.6535" x 2.646"

Generally speaking, in propellers, Diameter = thrust, Pitch = speed. It's a matter of finding the right combination. Then there are factors such as 'lifting props', etc.

It is very mysterious and then you add in the WTF factor like ABC and Prather and their cryptic numbers. Then comes Graupner, etc. Who the hell knows what some of their numbers mean? You need cross reference charts, etc.

What is the answer? Ask everybody you know that's running the same boat what prop they are using!

[bwells]

The octura x642 and the Graupner 48 have the same final pitch of 2.64 where as the Octura is 42mm and the Graupner is 48mm, quite a big difference. I like your general rule of pitch equals speed and diameter equals thrust. Thanks for the tip. I'm trying to fill in some holes in my prop bucket and noticed the Graupner, I have the 642 but will get the Graupner and compare them.

[Flying Scotsman]

The other equations are motor, power and hull design. All in all, very confusing. The best way IMO is to experiment and use a data logger, gps and your eyes.

Douggie

[bwells]

Yep, I have a GPS and an infrared heat gun, no data logger, but do have eyes that sort of work. I have a lot of props to use on 3 different boats so I hope my battery stash will prove to be sufficient! I have a chart made up to log prop, ESC temp, motor temp, speed,Etc. Are the caps on the ESC the best place to take temp reading?

[ericspeed]

Im new at this, so please, any info will help. If my motor has a rpm of 35,200 what props will i need to go over a 100mph? Im runnig twin scorpions (hk-4035-800kv) on 12 cells, the boat is a 41 falcon

[bwells]

100 MPH!! You are way above my league. I am sure that you could get the answers on this forum but you would get more "hits" if you posted another thread, something like 'twins in a 41 Falcon". That would be an eye catcher and would love to hear the answers. Good luck and welcome to this forum, lots of good info here.

[m4a1usr]

Im new at this, so please, any info will help. If my motor has a rpm of 35,200 what props will i need to go over a 100mph? Im runnig twin scorpions (hk-4035-800kv) on 12 cells, the boat is a 41 falcon

There are some hulls that no matter what you power it with will never achieve an extreme speed. They just wont get there. Take the SV27. Great boat. Handles well but time after time those who have pushed the boundry cannot break past its limits. Its all in the design and ride charcteristics. I dont know the Falcon you have but unless you want to dedicate some serious problem solving your going to have a difficult time pushing that hull to those speeds you want. At certain speeds aerodynamics begin to come into play and Cats like to trap air under the hull. Making it tough to keep them on the water. There are tricks and special modifications that can done to push certain designs beyond what might be considered the wall but at some point you will find there is a limit. And power alone will not break that limit. I cant say how fast you will go but if you want to challenge yourself and find that wall I bet you get a great education out of it. For most of us its all about the learning experience.

John

[bwells]

Well said.

[ericspeed]

100 MPH!! You are way above my league. I am sure that you could get the answers on this forum but you would get more "hits" if you posted another thread, something like 'twins in a 41 Falcon". That would be an eye catcher and would love to hear the answers. Good luck and welcome to this forum, lots of good info here.

thank you for the info, I'll try that..

[ericspeed]

There are some hulls that no matter what you power it with will never achieve an extreme speed. They just wont get there. Take the SV27. Great boat. Handles well but time after time those who have pushed the boundry cannot break past its limits. Its all in the design and ride charcteristics. I dont know the Falcon you have but unless you want to dedicate some serious problem solving your going to have a difficult time pushing that hull to those speeds you want. At certain speeds aerodynamics begin to come into play and Cats like to trap air under the hull. Making it tough to keep them on the water. There are tricks and special modifications that can done to push certain designs beyond what might be considered the wall but at some point you will find there is a limit. And power alone will not break that limit. I cant say how fast you will go but if you want to challenge yourself and find that wall I bet you get a great education out of it. For most of us its all about the learning experience.

John

thank you, im sure im going to hit some walls, but i"ll let you know the end results.