Mercruiser 888 Unexpected Prop behavior?

[ratdude747]

Results:

On the 21 pitch prop, I was able to hit a WOT of 3950-4000RPM, right near the middle of the range. Top speed was 45-47mph in the most favorable wind/current. Fuel economy was good too. Same results as the first time other than the RPM... maybe back then I did hit 3900 or so back then and remembered it wrong (since I also had the wrong WOT range in my head???).

So, for running two people no tubes, it seems 21 is acceptable. The 19 is probably good for tubes and other high loads... so having both options is the way to go?

 

[ratdude747]

(Delete this, I have fat fingers)

 

[ratdude747]

Here's a video of one of the full throttle tests. In this one I topped out at 46mph. An earlier run (not videoed) hit 47 briefly, but that's splitting hairs. Turning about 4000 RPM.

View attachment AQMCTfz4RC66yrHOl35UAvEbyw6ycx7Msn4BZkf9ktaHroFtCy0Ttnp1OQwkzHB7gAnv9Ghvwwf6EzTE2gfqsOijFlADXt...mp4

 

[Texasmark]

My experience with 4 blades is they tend to lift the stern on my hull. Usually resulting in trim making little to no difference as well.

Try the 19 and see if you get in the ballpark for RPMs. If you were closer I'd loan you my stainless 19 to test just because. That prop has run like magic on a lot of hulls.

4 blades are advertised to be stern lifters.....primarily at the lower speeds where 3 blades don't perform as well. I had 3 and 4 blade props and they proved the point and also the effect of the additional blade reducing top end.

 

[Pmt133]

4 blades are advertised to be stern lifters.....primarily at the lower speeds where 3 blades don't perform as well. I had 3 and 4 blade props and they proved the point and also the effect of the additional blade reducing top end.

Exactly. I tried more or less the whole merc catalog on my hull. Coincidentally merc has it right. 80s vee hulls like the mirage.

I'm trying to get my hands on another (larger pitch) enertia and enertia eco just to see how it runs. It's fun but also time consuming playing around with all these pieces. I can say merc probably puts more R&D into their lineup than anyone else and it shows from my testing.