Thanks Thanks:  0
Likes Likes:  0
Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread: prop finish

  1. #1
    Team Member Roflhat's Avatar
    Join Date
    Jul 2011
    Location
    Scotland
    Posts
    166
    Post Thanks / Like

    Default prop finish

    I've been trying to read up about this online but there are clearly mixed views.
    What kind of finish gives the best results on a prop? some people say polished but others say its best when you used 120-grit sandpaper

  2. #2
    Team Member zul8tr's Avatar
    Join Date
    Oct 2008
    Location
    Orlando, Fla
    Posts
    509
    Post Thanks / Like

    Default

    Here is an interesting link on the subject, site owner Ron Hill is in it

    http://www.screamandfly.com/showthre...sh-prop-or-not

  3. #3
    Team Member Roflhat's Avatar
    Join Date
    Jul 2011
    Location
    Scotland
    Posts
    166
    Post Thanks / Like

    Default

    interesting read, not a very definitive answer though

  4. #4
    Administrator Ron Hill's Avatar
    Join Date
    Nov 2004
    Location
    Tustin, California
    Posts
    3,407
    Post Thanks / Like

    Default Ron Hill's Thoughts

    I'll add my thoughts here. Over the years, in kneeldown boats I've never seen a satin finished prop in the inspection area of the finals at an APBA Nationals. Usually, the props are thin as hell and sharp as a razor.

    BUT, I used to make OPC props like that and they usually broke after not much use and that was in the 150 HP days.

    I my onw testing, I believe a satin finished bottom is in fact faster than a polished bottom. Jay Smith said 400, but I like almost 80 grit...sanded long ways, which brings us to the question of satin finished propellers. I would not want the satin to go across the blade. I try to make the satin lines follow the rotation of the blade, not exactly but in that motion. I am convinced that Speed coat is slower.

    The trailing edge is very important in how a props really runs. We, family relgion, always took a very sharp knife and ran it across the trailing edge of a blade to where there was a slight burr, just before a Kilo run or a Nationals final heat.

    The slightest "EDGE" is what you are looking for in racing. Polishing, under a microscope, tends to roll off the back edge. But this can be sharpened back..

    Bottomline, if the prop works, keep it...Polishing a satin finished prop could ruin it. Same as satin finishing of a polished props could ruin it. I take a machine polished Mercury Bravo One, thin it, balance it, sharpen the edges, and satin finish it and it picks up three mph and gets on plane faster. Nothing I did SHOULD make it plane faster, I wouldn't think anyway, except the satin finish.

    Sand blasting or glass beading the trailing edges, to me, was done to cause the cup to "Slip". See, I believe cups slow props down......Anyone want to go there??

    DeWald seems to own Formula One, his props are polished. Most Formual One dudes don't use Merc Props, but I've heard it is a customer service (He loans you several to buy one). I've heard Mercury sells you one or several. When I've reworked DeWalds, the winningest one I did was satin finished.

    Jim Boo has built some damn fast props over the years. His polishing is close to perfect.

    All the above are my opinions. I guess that is what makes "HORSE RACE".

    Bottom line: I don't know that there is an answer...maybe, I should run for politics!!!

  5. #5
    - Skoontz's Avatar
    Join Date
    Apr 2006
    Location
    Encinitas, California
    Posts
    581
    Post Thanks / Like

    Default

    Ron let me axe sumpin. Is it not easier to see stress cracks and would be trouble areas with a polished prop?
    Don Hendrich would polish my props and then sharpen the edges so you would get a mirror finished prop and then about 1/4" of the edges ground sharp. I even smeared a little shaving cream on my left arm and sliced the hair off one night when I had a few too many Heilemans Old Style beers to show my buddies.... You could see the machine marks running the same direction as the edges parallel along the curves if that's the correct term.
    Bill Schwab
    Dirty Deck Brewing
    Company

  6. #6
    Team Member zul8tr's Avatar
    Join Date
    Oct 2008
    Location
    Orlando, Fla
    Posts
    509
    Post Thanks / Like

    Default

    All my props from Pinner were satin, I never polished them out and they ran well in 25ssh. If they were polished I doubt that any cost effective measuring device could detect the difference under controlled real world test conditions because of the many variables that would be hard to keep constant. No doubt controlled lab conditions could detect a difference in drag (interesting test for a ventilated surface piercing prop) but not the same as real world running.

    As for bottom finish tried gloss varnish and sanded flat black with 400 in long direction and sanded was better feel with my SOTP Buttmaster (patent pending). BTW Bob Wartinger, Bob 110 records as of 11/04 and read he uses sanded bottoms.

  7. #7
    Administrator Ron Hill's Avatar
    Join Date
    Nov 2004
    Location
    Tustin, California
    Posts
    3,407
    Post Thanks / Like

    Default My Dad Played With A Lot of Water Skis

    My dad had a small cabin at Lake Elsinore. He made his own water skis, he had heard of them, but never seen any, He made them out of 1 X 8's and actually made 20 or so sets. One thing he did while fooling with his skis, was to try different things on the bottoms to reduce drag. He always said sanded varnish with square trailing edges had the least drag. When fiber glass bottoms came into being, he always sanded the fiberglass and made sure the small grooves ran long ways.

    As far as Race Props go, I have yet to see a SATIN FINISHED propeller win a Nationals. I'm not saying it hasn't happened, I just have never seen it. The last time I was in the H1 pits at San Diego, I was actually quite surprised to see how highly polished all the props were on these turbine powered boats.

    Thin and sharp have always been fast.......but they don't always last!

  8. #8
    Team Member Roflhat's Avatar
    Join Date
    Jul 2011
    Location
    Scotland
    Posts
    166
    Post Thanks / Like

    Default

    great replies, I was thinking in terms of the air on the prop, which when sanded is obviously more. In boat racing all the top offshore boats have stepped hull to reduce contact area with the water, does the same principle apply to propellers?

  9. #9
    Administrator Ron Hill's Avatar
    Join Date
    Nov 2004
    Location
    Tustin, California
    Posts
    3,407
    Post Thanks / Like

    Default I Don't Think So!

    You want a prop blade to push water, not slip through it. I'll try to post some pictures tomorrow of some prop surfaces!

  10. #10
    Team Member zul8tr's Avatar
    Join Date
    Oct 2008
    Location
    Orlando, Fla
    Posts
    509
    Post Thanks / Like

    Default

    No, stepped surface does not apply to props. On a hull the steps reduce bottom surface area and introduce air downstream of the step thus less drag with the air entrained mix. The ocean racers I have seen have rough surface where the water contacts the bottom. It is a laminar vs turbulent boundary layer issue with the drag component on the bottom. As Ron Hill correctly notes on props you want the water to stay in contact with the push face (aft facing for thrust. It of course is complicated by the surface piercing fully ventilated props that are used on the race hulls which operate with turbulent boundary layer air mix on the push face.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Finish on 20H Conversion LU
    By RogerH in forum Technical Discussion
    Replies: 75
    Last Post: 06-07-2014, 03:15 AM
  2. over prop exhaust v thru prop exhaust on 60hp evinrude
    By phillnjack in forum Technical Discussion
    Replies: 38
    Last Post: 05-09-2013, 02:17 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •