Prop Slip

[harmanoff]

So ive seen this recently browsing through posts, and have tried to use the prop slip calculators but it always gives me words and NaN or infinity in the box nothing else. I am trying to figure out how to use it so when i get my new 17p prop i can see what it's slip is

 

[QBhoy]

So ive seen this recently browsing through posts, and have tried to use the prop slip calculators but it always gives me words and NaN or infinity in the box nothing else. I am trying to figure out how to use it so when i get my new 17p prop i can see what it's slip is

Hi. I use the Mercury calculator
You’ll need;

Speed at full throttle in gps
Rpm at full throttle
Gear ratio
Current prop pitch

A real performance hull with power can achieve 2-4% slip, well propped. Average to aim for would be 7-10% generally. Picture of mine below

 

[harmanoff]

ok so my gear ratio is 2.33:1 how would i put that in?

 

[Texasmark]

The gofast.com calculator is simple. 2.33 is 2.33, RPM is in HZ...5500 is 5500, prop pitch is in inches...19P is 19. Push the title block over Max Speed and you get max speed in MPH....that's a screw turning in wood, not a propeller turning in a movable volume....water. Jump over to your GPS Actual Speed and insert it in MPH. Click on the Prop Slip title block and the block will fill with your slip in percent. Piece of cake.

Single digits and you are doing great. If you get up to 20% you have a tub......or maybe a TUG towing barges. (sorry just slipped out). Grin

 

[harmanoff]

ok cool, i wasnt sure how to go about since it kept throwing errors and was like well how the hell does it work lol. plus with my gear ratio being 2.33:1 i was like how does that even begin to be entered!!

 

[harmanoff]

With my current setup: 15p Prop, WOT 6000 RPM Down river at 31 MPH i have a 15% prop slip, i know the RPM is over the 5500 max but was testing the prop to see if i need a new higher pitched one which i do. According to the mercury dealer here when i put the new prop on i should gain 2-4 MPH while being at 5400 RPM at WOT or alil lower. That shows a 9% prop slip

 

[QBhoy]

Apologies for the repeated posts. Phone was playing up !

ok so my gear ratio is 2.33:1 how would i put that in?

2.33

 

[QBhoy]

was

With my current setup: 15p Prop, WOT 6000 RPM Down river at 31 MPH i have a 15% prop slip, i know the RPM is over the 5500 max but was testing the prop to see if i need a new higher pitched one which i do. According to the mercury dealer here when i put the new prop on i should gain 2-4 MPH while being at 5400 RPM at WOT or alil lower. That shows a 9% prop slip

you won’t get too much better than 9% with an ally prop and that kind of speeds. That will be a theoretical speed just using maths.

 

[harmanoff]

I will be getting it friday and slapping it and going for a test drive! will see how it goes!