Prop Finish?

[jaxracer]

Recently been getting into doing some of my own prop work when I thought of an aspect that I hadn't really considered before, prop finish. With something turning at 30,000rpms, I feel like that's an important discussion.

When I think of a prop surface, I relate it to sanding on the bottoms of our boats, a slightly rougher surface=less hydro drag while a slicker or polished surface=more drag. In that same note, I would associate a rougher surface with less prop efficiency and vice versa. Is that correct?

Also, what would happen if you made the front "work" side of the blade one finish, while making the backside another? Or using something like Rain X on the non cupped side of the prop since it doesn't need to be efficient for less drag.

Just trying to get some feedback on what works "best" and what's already been tried?

 

[Marty Davis]

Mitch:

Impressive that you are thinking about things like that. MOST people don't consider this type analysis.

My exerience is that a polished prop surface is not nearly as efficient as one that is slightly rougher. I know that Andy Brown uses a finish that is not polished and I do also. Back many years ago when our engines didn't have a smuch torque for launch, I found that a polished prop often times cavitated without hooking up while the exact same prop with a scotchbrite type finish hooked up fine.

Based on my past experiences, I would suggest that you use the ScotchBrite type finish.

Now, I usually spray my props with Dykem Steel Blueing (Red Color) and it essentially has a rougher finish. I do that to see the areas that wear away after running for a while.

Keep thinking like this, it is something that seems to be lacking with most people.

 

[charles siler]

Also how do factor in hard and soft water . Here in Alaska we have soft water and on my 90 rigger I run a 1667 with a 6 cup.

I attended the fall nationals in south Carolina last year and I ended up running a cut down 1667 thrash prop that I borrowed to run the race . Thanks Charlie

 

[DaveThynne]

Air density could have been a big factor in the props you ran charles

 

[Patrick Mulvany]

Mitch,

You got your head screwed on right!! Polished is pretty but rough and ugly works!! At best I just wire wheel my props after adjusting and balance/sharpen.. After that they just get homely with the water in Fl. and Ga...

Later!!

Pat

 

[wayne middlemiss]

Why not just bead blast them after all the critical work is done to bring back the as cast finish.

 

[charles siler]

Air density could have been a big factor in the props you ran charles

Dave the air density here is 80 to 90 the air at Charleston was 100 to 125 .

 

[Andy Greene]

air density plays a factor Im sure , but that said- I have tested a boat otw to a neighboring pond for a race on the same day 50 miles apart and had to prop down to get on pipe- water plays a large factor in my worthless opinion, the air in Florida didnt change THAT much in a few hours time.

I will also note the same setup with the larger prop worked perfectly at three other area ponds in hugely varying air and temps .

 

[John Knight]

Andy told me some years ago he uses a satin finish to reduce the cavitation, especially during launch. I have used that since.

Charlie - your numbers for the Charleston air density are slightly off. The correct numbers almost always go from 95 to 104. I would hate to see a high density number of 125 - few people would ever get a needle rich enough to go with the real dense air.

 

[Ray Sametz]

Andy told me some years ago he uses a satin finish to reduce the cavitation, especially during launch. I have used that since.

Charlie - your numbers for the Charleston air density are slightly off. The correct numbers almost always go from 95 to 104. I would hate to see a high density number of 125 - few people would ever get a needle rich enough to go with the real dense air.

Yup that AB swirl is where is at, for us novices scotchbrite works. As far as air density it can be deceiving, it's the O2 in the air that's a bigger factor. Used to run at a lake at sea level near a major highway AD was 94. Raced in a state park 900 ft. above sea level, AD was 85. Logic would say go leaner, but needed a super rich setting to make power due to all the O2 from surrounding trees and no pollution. Bet the air in Alaska has more O2 then Charleston. OMHO.

 

[Marty Davis]

Why not just bead blast them after all the critical work is done to bring back the as cast finish.

The guy that I sold Crapshooter to, Gregg huey, did props and he used glass bead to finish his props. They worked very well that way.

 

[Terry Keeley]

I like the 80 grit 3m bristle disks for the face and 400 grit wet/dry for the back:

http://www.fdjtool.com/ProductInfo/10.2E_9113.aspx

Moore sanding disks are great for roughing out the face:

http://www.fdjtool.com/ProductInfo/10.2E_01081B.aspx

 

[shoboat]

Guys,

For the face Dremel makes a quick change radial brush wheel 1" in diameter with a 36 grit.

For the rest of the propeller, hub included, a 3M EXL 2 S Fine wheel approximately 220 grit.

The only problem with beading is you throw off the final balance ever so slightly. Sand blasting the propeller with

Walnut shells works great for a nice finish. Some propeller shops use that finish for water ski propellers.

Some of the latest surface finishes are with a CNC machined swirl pattern machined into the face.

On ABC's latest Game Changer Propellers series Jim is molding a specific finish on the face of the blade.

Plenty Of Options Out There,

Mark Sholund

 

[John Beardslee]

My visits to Mercury and OMC a hundred years ago told me that a surface that was arrived at using 400 grit medium was proven to be the most efficient.

Thanks, John

 

[El Zorro]

I have been sanding my props and the bottoms of my monos for years with 220 grit emery cloth. Even sanded the bottom of my big hydro when I was racing them. Many of the big boat guys didn't get this. They liked the gloss finish. I was just the guy that use to play with toy boats..........

Dick Tyndall

 

[John Beardslee]

Hi Dick,

When I was running big boats some of the guys used a product called "foam glass" to cut linear lines on the running surfaces of their boats, the stuff smell like rotten eggs, but it cut fast.

Thanks, John

 

[moparbarn]

I have been sanding my props and the bottoms of my monos for years with 220 grit emery cloth. Even sanded the bottom of my big hydro when I was racing them. Many of the big boat guys didn't get this. They liked the gloss finish. I was just the guy that use to play with toy boats..........

Dick Tyndall

Me too, Dick. Since the days of red stripe mercurys (-;

 

[El Zorro]

I actually had a 2 foot by 2 foot piece of the foam glass that Gary Pond gave me but I really didn't like that. Maybe the rotten egg smell had something to do with that........!

Dick Tyndall

 

[Ray Sametz]

I actually had a 2 foot by 2 foot piece of the foam glass that Gary Pond gave me but I really didn't like that. Maybe the rotten egg smell had something to do with that........!

Dick Tyndall

Sure it just wasn't an Aire Galleta.

 

[El Zorro]

If you ever smelled this stuff it would make you want to puke. A lot worse than isle 5 at the Piggly Wiggly.............

Dick Tyndall