Pitch vs prop size

[Mulisha]

Hi I'm looking for some info on prop sizes and the pitch. I understand about torque roll with large props and the amp associated with different sized props. But would like to know about going up in pitch or in size and the effect positive and negative.
Example 43x1.4 or 42x1.6 the later has more total pitch but the first has a larger diameter prop and how will they effect the boat. Mainly looking at cat and a tunnel hull so I know both will run better on certain props.

[Jason4636]

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[NativePaul]

The 42x1.6 will give more speed and more prop walk, the 43x1.4 will give more acceleration and more torque roll.

[Mulisha]

So with a twin cat counter rotating I should feel that as bad as V or tunnel hulls

[NativePaul]

What? I fail to comprehend any meaning form what you just said.

Torque roll isn't such a problem for a decent oval cat or a tunnel as it can be for a mono due to the inherent lateral stability of the twin hulls.

Prop walk can be an even bigger problem for a cat than a mono as all the aero lift from the tunnel means there is less hull in the water to counteract it, a higher deadrise angle wheter on a mono or a cat will reduce the effect of prop walk, as will lowering the prop.

[Mulisha]

Sorry I meant shouldn't see those effects. Won't the props counter rotating cancel the prop walk and torque roll?

[ReddyWatts]

PROP Pitch/inches

X437/3-- 2.072
X438---- 2.100
X440---- 2.198
X440/3-- 2.198
Y536---- 2.200
Y537/3-- 2.279
X442---- 2.310
X637---- 2.368
X445---- 2.478
X640---- 2.512
X447---- 2.590
X447/3-- 2.590
X642---- 2.640
M545---- 2.655
X448---- 2.660
X450---- 2.758
X450/3-- 2.758
X645---- 2.832
Y547---- 2.849
X548---- 2.850
X452---- 2.870
X452/3-- 2.870
X646---- 2.896
X646/3-- 2.896
X455---- 3.038
X455/3-- 3.038
X648---- 3.040
X457---- 3.136
X457/3-- 3.136
M650---- 3.190
X460---- 3.304
Y557---- 3.449
X560---- 3.540

X427---- 1.498 0.125
X430---- 1.652
X431---- 1.708
X432---- 1.764
Y531---- 1.877
X435---- 1.932
X632---- 2.016
Y534---- 2.059
Y535---- 2.125

[Mulisha]

I'm more interested in the effects of small prop high pitch against big prop small pitch, and how they affect the boat

[electric]

From what I know it seems you can get a bit more speed with a higher pitched prop (abc 1.6) pitch than a simliar prop octura 1.4 pitch with a larger diameter for the same amount of amps. This is because to get the same total pitch with the "x" octura you need more diameter than you do on the ABC. There is also the issue of which prop is more "efficient". I am discovering that over 60mph you are really looking for higher pitch (cupping the prop, bigger pitch) because the diameter becomes to large and that causes some amp draw issues as well as other handling issues.

Most of the "custom" prop makers seem to be cutting down the diameter of the x props and pitching them up. Same effect as I just described above. There is a a whole "lot" of knowledge about props out there, but this is my simple observation.



Then there are one thousand other issues to balance. Prop lift, thrust cone, 2 blade vs 3 blade, cupping, polished or not, cutting down the leading edge.....it just goes on and on.

By the way 2 blade is generally better, x props should have the leading edge cut down like an "M" prop does.... there are always exceptions to the rule though...

[h2o 1]

http://forums.offshoreelectrics.com/album.php?albumid=991
Click and read. Theres alot of great info on props in Sweetaccords album. I look at this weekly!lol,Mark

[Mulisha]

thanks heaps h2o 1 that link was great so much info on there still looking through all of it

[BHChieftain]

Sometimes a lower pitch prop can actually yield more speed-- sometimes the higher pitch prop does not let the motor reach full RPMs. I had a 6 series prop on my 29" mono with a 2200kv neu motor and it was running a bit too warm, I dropped down to a 4 series prop with less total pitch, and the boat ran cooler AND faster... what a surprise!

Chief

[martin]

Quite often going down in pitch but up in diam (overall pitch will be lower even though diam is larger)will yeild higher speeds, larger diam is sometimes more efficiant.