Shocked by prop results

[SkiDad]

A few years ago I picked up a 15 pitch stainless prop on Craigslist - just some light scratches and nicks - nothing really serious (i thought)

anyhow it was slower top end to my aluminum prop but cruised slightly better. Didn't run it often. Last year, just for kicks, I threw it on with my different lower unit (2:1) and it turned out to be a good slalom ski prop with my new found torque. So this winter I decided to wet sand it and polish it just to make it look nice. Spent about 8-10 hours over the winter. I've been out 3 times this year now and i'm getting 2 MPH increase across all rpm ranges and my RPM dropped 300.

I did not expect that at all - i wonder why ?

RPM	Before Polish	After Polish
3500	21	23
4000	26	28
4500	29	31
5400 (wot)	35
5200 (wot)		37

 

[Sea Rider]

Probably the smooth non pourous finish has something to do with prop gripping better, or whatever it does to account for more speed throughout the whole throttle range as opposed to when was previous painted.

Happy Boating

 

[WIMUSKY]

I would think the opposite. A mirror finished prop would have less grip..... But, results are results........ Nice work polishing btw..........

Were the water conditions identical when the polished prop was tested? Did you have exactly the same weight in each test? Same amount of fuel? Was the weight distributed exactly the same way? But since the rpms dropped and the speed went up, one would think you had more forward bite alright.

 

[JaCrispy]

Probably the smooth non pourous finish has something to do with prop gripping better, or whatever it does to account for more speed throughout the whole throttle range as opposed to when was previous painted.

Happy Boating

The boundary layer effect.

Liquid sticks to polished surfaces more than rough surfaces. So it could be the prop grabbing more.

 

[gm280]

I seriously don't have any answers for the differences, but I do have to say, you did an amazing job with the polishing. Very nice looking... :thumb: :thumb:

 

[SkiDad]

thanks for the compliments the pictures are a little misleading b/c of lighting. Up close you can still see scratches,etc. but it did come out really nice.

I'm starting to think that the hole shot might have slowed down a tad, or my slalom form was a little bad the first time out. But if slower hole shot I guess I can just hit it with some 400 grit.

the only thing i can think of is that rounding the edges a little and cleaning up the minor nicks freed it from some disturbances.

 

[JaCrispy]

What did you use on it? I just picked up a LaserII, wouldn't mind giving it a little bling.

 

[SkiDad]

as far as wet sanding, i did it by hand using some sanding blocks in 200, then 400 grit, then 800 grit pad to get out the scratches I made. Then I got one of those round polishing wheels at Harbor Freight for under 10 bucks and hooked it an electric drill and used some polishing rouge. I had some of the grey color stuff available but I think harbor freight has some of that too.

 

[SkiDad]

Were the water conditions identical when the polished prop was tested? Did you have exactly the same weight in each test? Same amount of fuel? Was the weight distributed exactly the same way? But since the rpms dropped and the speed went up, one would think you had more forward bite alright.

yes, same weight and water conditions as past tests.

The fastest I got it run last year was on a 55 degree day and 60 degree water and it turned 5500 and just cracked 36 and that was just me and 1 kid and no junk in the boat.

 

[steelespike]

Sometime ago someone polished an aluminum prop and got an improvement.As I recall not like your ss prop and it didn't hold up.
Noting your prop seems to be cupped I wonder if it improved because the paint was shading the cup effectiveness.

 

[SkiDad]

my pictures aren't the greatest - it just what I had from when i first got it - it wasn't painted, but rather just a dull stainless look.

i wonder what result I will get it i just sand the rear sides of the blades - something to play around with.

 

[JaCrispy]

I just did my new (used) prop with Autosol and some 0000 steel wool.

 

[SkiDad]

I just did my new (used) prop with Autosol and some 0000 steel wool.

Nice!

 

[JaCrispy]

Thanks, you inspired me.