Prop experiments

[iwombat]

I currently have an over-propped boat and need to go down in pitch. My spare prop is what I believe is the right pitch. I'm considering putting it on and trying it out. If it performs correctly, I'll buy a new or rebuilt prop and keep the one I have as a spare.

However, there's a small chip in one of the blades about halfway back. It's roughly 1/8" deep by 1/4-1/2" long. Is this enough of a chip to invalidate the test with this prop?

 

[WillyBWright]

Re: Prop experiments

Nah.

 

[iwombat]

Re: Prop experiments

Thanks, that was my thought. But, I needed to be sure before swapping a prop and taking the boat out.

 

[sabastianunf]

Re: Prop experiments

I had a 3 blade that was a little rough arougd the edges - no real bad chips. Anyway I bought a new prop based on the worn 3 blades performance and after running my new prop I am convinced that my worn 3 blade was slipping badly and caused me to buy the wrong prop. I would reccomend calculating the slippage of your current prop before assuming the damage does not affect performance.

 

[iwombat]

Re: Prop experiments

My current prop is fair to good. It is, however, too much prop. My spare is what I think is the right size, but that one has the chip.

I'll try out the spare and assume the chip makes a small impact on the results.

 

[sabastianunf]

Re: Prop experiments

Lots of websites have slippage calculators - all you need to know is what gear ratio you have, how many RPM's and speed you run at WOT. I think that normal slippage is @ 7-10% if you run higher than that then the damage to the prop is having a significant impact on your performance.

 

[Bry21317]

Re: Prop experiments

Quick question on this also, will aluminum have a higher slip than SS?

Not trying to Hijack the thread, just figured I would throw the quick question in here, as you were just stating about the Slip.

Thanks,
Bryan

 

[walleyehed]

Re: Prop experiments

iwombat, normal slippage would be around 15%...7-10% would be for a finely tweaked set-up. Aluminum is less efficient than SS in most cases, and, there is a world of differences in SS designs.
Most will choose very blindly and not know the difference, so when you run your numbers, remember to include prop model and size, pay very close attention to RPM as well...5000-5200 as a top RPM example is not good...we need to see a good figure such as 5150 steady, or 4500 steady, etc....