Propeller forum gone?

[Matthew A.]

Anyhow...
Hi Frank,
Upon looking up information on a new prop, [using Iboats Force prop finder] I read that if running an uncupped prop and switching to a cupped prop one should go down in pitch by 2. However, I also read that those with power trim do not need to make a reduction in pitch. And my question is.......why, with power trim is such a reduction not necessary?
I ask because I switched to a cupped prop of the same diameter and pitch as my original OEM semi-clever prop and found the cupped prop to be abit too much prop regardless of how I trim the motor.

 

[bowhuntrrl]

Re: Propeller forum gone?

Prop forum is still there, at least when i just looked !!!

 

[WillyBWright]

Re: Propeller forum gone?

Prop forum is down below the repair section in the General section. You're changing styles of propeller. Pitches will often not translate equally. When they speak of cupped and uncupped, they're speaking of conventional props with and without cupping.

 

[Texasmark]

Re: Propeller forum gone?

The number most use is drop 1" not 2.

Agree you have to stay with apples and apples. Props are all unique and you can't go jumping around brands and types and expect to have any sense about it. There isn't any. The only way to really know is to run it. Sorry, but dats da way itis.

Mark

 

[kenmyfam]

Re: Propeller forum gone?

I run a 14" X 17" regular OMC prop on the outfit in my signature. It gives 45mph at 6,200 rpm (gps verified)
I also use a 14" X 19" cupped OMC prop that gives 45mph at 5,300 rpm (gps verified)

17" comes out of the hole like a rocket. 19" comes out fine but a little slower. My handbook says WOT between 5,000 and 6,000 rpm.
I guess my next investment will be a 14" X 17" cupped and hopefully I will get right between the 2 results so far.
My outfit seems to do the same speed no matter what the load / prop combination I have in there.
Do not mean to hijack this thread, just sharing my experiences.

 

[Texasmark]

Re: Propeller forum gone?

Well Ken, you dropped 900 rpm's and if you figure your 2" at 250 each and another inch for cup you are at a theoretical 750 which is pretty close to your stated rpms.

I think what I see here is that your rig requires X hp to run at 45 mph and your engine torque curve falls off at the higher rpm's; so hp is still torque x rpm's.

Some boats, like mine, increase speed with an increase in pitch.....obviously to a limit. So, the faster I go, the less hull I have in the water, so the less hp it takes to run it, so it goes faster.

Does that make sense??????

Mark