Internet Prop Calculators

[Little35]

Has anyone else ever tried one of these propeller calculating programs that are used on some of the prop websites? I tried this one with my current info and it comes up with the some of the same performance values that I have come up with.

http://www.propgods.com/content/prop_calculators.aspx

These are some others that I have found.

I wanted to add this one
http://continuouswave.com/cgi-bin/propcalc.pl

http://www.hillpropellers.com/propcalc.html


http://www.castlemarine.co.uk/pitch.htm

I understand from the other answers to my other thread that the best way is to put it on your boat and test. I just wondered if these are usefull to get you as close as possible before you buy a new prop.
Thanks.

[Dutchman]

I use them all the time, they work well.

[tn_pete]

Here is what it shows mine at?
This does not sound right? Any help on this ?
pete

Engine
RPM 4900

Gear
Ratio 2.1

Propeller
Pitch 17

Propeller
Slip 0.01

Speed
MPH 37

Same on thecontinuouswave.com is 1.50

[San Chan]

Here is what it shows mine at?
This does not sound right? Any help on this ?
pete

Engine
RPM 4900

Gear
Ratio 2.1

Propeller
Pitch 17

Propeller
Slip 0.01

Speed
MPH 37

Same on thecontinuouswave.com is 1.50



Mine is 8.91 Slip off all 3 www.site . I don't think the Slip can be that low like yours, can it?

[Dutchman]

I think the real world prop slip is always around 10%. Worst for aluminum props and better for Tweaked stainless props.

[staylor]

...and as Dutchman notes, the prop calculators don't work as well for these. For example, on a typical Trophy or Tempest prop the stated pitch can be 21, but if you actually measure the pitch, it will be around 19 inches at the leading edge of the blade, and about 23 inches at the trailing edge. This type of blade contour helps performance, but different boats will essentially run on different sections of the blade. As a real world example, at one time I ran a Baja 184SS vee hull with a 175 Evinrude and a blueprinted Turbo II 3 blade with 24 inch pitch. This was aimilar to a Merc Laser and had measured slip of 8 percent on the 63 mph Baja. I then bought a much larger/heavier Checkmate Pulse 210 and swapped on the same 175 Evinrude with the same prop. Speed was down as expected, and measured slip increased to 13%- but the rig still ran very well. Was the change in slip from the heavier rig- or was it just that the rig was running on the reduced pitch section of the blade. You really can't tell what is causing the difference- is it more slip or is it the progressive pitch. As another example, I have a reworked 23 Trophy Plus that slipped at 6 percent on my current rig. I decided to have the prop radically altered by cutting off about 20% of the blade area by removing the entire leading edge of the prop. The prop shop that did the work said I might have trouble, since with the low pitched leading edge section of the blade removed what was left was up around 24 inches average pitch and the motor should rev lower. Yet, when I ran the prop the slip calculated at 8% running the new average pitch of 24 inches. The moral of the story is to try every prop you can get your hands on if you want the optimum performance from your rig.
Doug

[tn_pete]

Mine is 8.91 Slip off all 3 www.site . I don't think the Slip can be that low like yours, can it?

That is what I was thinking. But all that I am doing is putting in the numbers I know and coming up with that.
Pete