Prop pitch verses diameter

[FE Wannabe]

Good question - Lift has to do with the thrust cone. I wide thrust cone produces more lift because the water is being directed more to the side so if you narrow the thrust cone more to the back this will reduce the lift. The shape of the blade versus pitch plays a major role as far as lift is concerned.

Note: This is true for sub-surface props only as submerged props are a whole new ballgame.

Thanks for the great explanation Chuck.

That leads me to another question.....
When you are "cupping a prop", what effect are you trying to achieve? Are you trying to increase the diameter of the thrust cone, thus creating more lift or are there other benefits?
Hydrodynamics is a whole new world to me.
Brad

[tiqueman]

That is a loaded question. It all depends on the setup ... and at this point there are to many variables to answer your question.

egneg, you beat me to it...

PS, Nice avatar

[egneg]

Normally cupping a prop reduces the thrust cone but loads the motor a bit more. Thus it becomes a game of back/bar cut versus cupping to get a desired effect but to not put added stress on the motor.

[egneg]

egneg Nice avatar

Thanks ... I like it!

[FE Wannabe]

Chuck,
So when you cup a prop, what part of the blade is being modified? Leading edge, trailing edge, or some other area? Sorry for all the questions, I am just trying to get a better understanding of how water interacts with the blade surface to produce different effects. Also I want to know so when I ask you to modify one of my props I know what I am asking for.

Thanks,
Brad

[m4a1usr]

Isnt a two blade prop more efficient? If so then whats the advantage of three blades?

The advantage of a 3 blade over a 2 blade is the acceleration out of the hole. The disadvantage is top end. You can loose rpm's. A single bladed prop (yeah picture that) is by definition the most efficient. Cupping can do several things depending on where it is applied. Cupping on the area immediate to the tip can change the rake. Cupping on the trailing edge changes the pitch. Dont confuse the two. Remember the rake lines run outward towards the prop tip. Pitch lines run parallel to the hub.

Here is a teaser. http://www.marineprop.com/propinfo.htm

John

[bwells]

On a recent thread, it was mentioned that a 2 blade is faster in the straights but a 3 blade is faster in the turns. The hole shot in full sized boats is gained with a 3 blade, (ie pulling a skier)

[ozzie-crawl]

doesnt the tongue reduce lift as well, if i detongue a x series prop making it a m doesnt that in theory make it a medium lift prop compared to its original low lift as the tongue pierces the water easier ?
one other question how does the grim props numbers work eg, 42 x 55
i understand its 42mm dia but whats its pitch it cant be 55mm unless that overall pitch,but that would then mean its pitch is 1.3"
no wonder props are called a black art, its like voodoo

[bwells]

Ozzie, good question on the grim props. I think I have a handle on the Octuras but the numbering on the others I have not figured out. Edit Ozzie, did you get that stage 5 motor that you ordered from G-Freak yet?

[ozzie-crawl]

Ozzie, did you get that stage 5 motor that you ordered from G-Freak yet?

no i think its coming stage 8 postage via kazakhstan
plus i still only have .187 flex drives thinking i may need 1/4" solid kryptonite drive shafts to handle the power

[tiqueman]

Hold off Oz, the stage10R-GT supercharged comes out next month Apparently, its so fast, with the right pitch and diameter prop, You only get to see it once. You hit the throttle and it rockets its way into another time w/ Doc and Marty McFly... Stupid fast man.. stupid fast

[bwells]

Does anyone know if the IMPBA has tried to get the vendors to standardize their products as far as numbering. Both motors and props would be great so as to make it more easy to decide between the available options.

[tiqueman]

That would make too much sense! Would be nice though.

[bwells]

Tiqueman, Ozzie order three, that is 3 times stage 5, stage 15, which is unheard of, for his rigger in order to send Andy home with his tail between his legs and straight to the pouch of his Kangaroo!

[Xcesive8]

Firstly i know NOTHING about props..
Im hopeless when it comes to these sharp shiny things.

But,
Im really confused after reading the above comments about 2 Bladers being better for top end speed than 3 blades.

Why is that alot of the German guys running Hpr cats are using 3 bladers for there SAW runs?
Go to this link and see speedlist.
http://www.pbs-passau.de/

Another example:
Why did Grimracer offer there "Rio 51 mono" stock with a 2 blader, and have a written on the side of the box comment saying "upgrade to the Grimracer 3 blader for more topspeed" ?

All this info throws me on all the above talk up there ^