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Thread: propellers with leading edge roll/cup ?

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    Default propellers with leading edge roll/cup ?

    a few questions for the prop guru's .

    Over the last few months I have read a lot of posts on the internet where people have talked about having the LEADING EDGE of their props rolled/ cupped.
    Many have said about it giving less slip numbers and better Holeshot, but losing a touch on the top end.
    Some have said it did not lose on top end due to the slip figures dropping and the water not slipping off the prop so much.

    So I am wonder if we take a propeller of say 13 x 20 with just trailing edge cupped and add a leading edge roll would this lower the pitch slightly ?
    Also exactly what part of the leading edge is rolled to give the prop a better bite.

    I have added cup to the tips of the blades to give a touch more bowlift and hopefully a touch less slip, for my particular prop I need to drop the slip dramatically.

    Some people have for example had a OMC srx prop cupped on the blade tips and reduced slip by around 5% and gained more bow lift from the prop with no loss in
    top end but dropped rpm by a couple of hundred.
    I take it by cupping the tips adds a touch of overall pitch to the prop.


    so here are a few questions I would like to know more about.
    1/ Would adding a bit of leading edge roll drop the pitch slightly to bring back the rpm and give more bite on the holeshot ?
    2/ would adding leading edge roll interfere with the prop running at a surface application , I.E not work at surface or be detrimental to oval speed.
    3/ will a leading edge roll make the prop lift the stern or lift the bow.
    4/ what are the downsides to having this roll on a prop be .

    There is obviously a lot more to this adding cup/rolling the leading edge, but not much information as to what the effects are and where on the blades exactly is the roll put.
    also is the roll on a stainless put there by cold hammering or would it need to be heated to do this type of thing.

    I know this is a bit of a mix of questions, basically I need to understand a bit more about what this rolling of the leading edge will actually do.

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    Administrator Ron Hill's Avatar
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    Default If I Had About Three Days To Spare......

    Quote Originally Posted by filthy phill View Post
    a few questions for the prop guru's .

    Over the last few months I have read a lot of posts on the internet where people have talked about having the LEADING EDGE of their props rolled/ cupped.
    Many have said about it giving less slip numbers and better Holeshot, but losing a touch on the top end.
    Some have said it did not lose on top end due to the slip figures dropping and the water not slipping off the prop so much.

    So I am wonder if we take a propeller of say 13 x 20 with just trailing edge cupped and add a leading edge roll would this lower the pitch slightly ?
    Also exactly what part of the leading edge is rolled to give the prop a better bite.

    I have added cup to the tips of the blades to give a touch more bowlift and hopefully a touch less slip, for my particular prop I need to drop the slip dramatically.

    Some people have for example had a OMC srx prop cupped on the blade tips and reduced slip by around 5% and gained more bow lift from the prop with no loss in
    top end but dropped rpm by a couple of hundred.
    I take it by cupping the tips adds a touch of overall pitch to the prop.


    so here are a few questions I would like to know more about.
    1/ Would adding a bit of leading edge roll drop the pitch slightly to bring back the rpm and give more bite on the holeshot ?
    2/ would adding leading edge roll interfere with the prop running at a surface application , I.E not work at surface or be detrimental to oval speed.
    3/ will a leading edge roll make the prop lift the stern or lift the bow.
    4/ what are the downsides to having this roll on a prop be .

    There is obviously a lot more to this adding cup/rolling the leading edge, but not much information as to what the effects are and where on the blades exactly is the roll put.
    also is the roll on a stainless put there by cold hammering or would it need to be heated to do this type of thing.

    I know this is a bit of a mix of questions, basically I need to understand a bit more about what this rolling of the leading edge will actually do.

    .
    When my two sons raced 45 SS, we had 26 propellers. When we decided we were getting out of 45, I went to Blythe with Steven Dawe and he test all 26 props in two days. There were 9 he wanted to try again. And or, try in a race.

    Just saying: Adding a roll to the leading edge can help the bite, but it also de pitches the prop. There is so many variables, an on board computer, is the only way to rack what you are doing to your prop. A computer tracks everything. We found in 45, a 64 MPH propeller was better than a 78 MPH prop. Hard to convince yourself of this until you see the computer model........or until the 64 MPH drives around on the race course.

    Cupping the trailing edge frequently slows the boat down.

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    Is rolling the leading edge like forcing it towards to the gearcase? Does anyone have picture before and after?

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    rolling or cupping the leading edge is the same way as the trailing edge.
    imagine grabbing the leading edge and bending up towards the nut of the prop.

    The srx that fits on the 56 cu in for example would bite better and give less slip figures, but would not be as fast top end, in theory, But if the slip figure goes down then it could be much faster.

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    There's a thread here called Face Cup. Is this what you are talking about? Smokin Joe had written a book , The Physics of Speed on Water, but I don't know if it has found a publisher.

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    dont know about face cup, I think that is more of progression on the entire blade ? maybe not.
    any idea where it is on the forum ?

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    I think way back when R. Allen "Papa" Smith was working with Michigan Propellers he "cupped" the trailing edge to strengthen it to be able to have a thinner blade. He also learned that it usually made the prop faster and increases acceleration. Cupping the trailing edge increases the pitch also and it keeps the water on th blade longer.

    He explained this to me a long time ago on one of our many phone calls.
    Dean Hobart

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    Okay,
    Ive bent leading edge away from the nut, "derolled" and it gives me better takeoff and overall performance for now. Oh and I think I have made trailing edge cup smaller with tighter radius than stock SRX.

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    Here is a brief description of prop factors from Smoken Joe (prof Joe Mccauley)

    http://www.mccauleyandson.com/html/props.html#improve

    Joe discusses leading edge blade angle

    Here is his paper on Scaling for Speed (some math)

    http://www.mccauleyandson.com/docume...d_on_water.pdf

    On Joe's book:

    http://www.mccauleyandson.com/html/physics.html

    email discussions I had with him the book is still being worked on and hopes to publish soon?

    On cupping the leading edge I think a rather abrupt bending over a short distance (cup) would be detrimental to prop performance and would disturb a clean blade entry into the water. As Joe explains in his paper the leading edge needs to be set at a pitch for a clean entry into the water and that is related to the angle of the leading edge area of the blade relative to the prop shaft centerline. Joe says doing a proper entry blade angle will improve acceleration and top end.
    " Three may keep a secret if two of them are dead" Ben Franklin
    " ------- well Doctor what have we got a Republic or Monarchy? A Republic he replies if you can keep it"
    Benjamin Franklin, 1787 Constitutional Convention, as recorded by signer James McHenry's in his diary at the Library of Congress

    Location: SW Orlando, Fl

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    Google " Face Cup Boat Racing Facts" .
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