propellers with leading edge roll/cup ?

[filthy phill]

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.

.

[Ron Hill]

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.

[hupiveneilija]

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

[filthy phill]

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.

[rumleyfips]

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.

[filthy phill]

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 ?

[DeanFHobart]

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.

[hupiveneilija]

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.

[zul8tr]

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/documents/scaling_for_speed_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.

[rumleyfips]

Google " Face Cup Boat Racing Facts" .

[Fastjeff57]

For what its worth.... I had a 32 foot cruiser w/ twin inboards (Mopar 360s). Port prop was a 16 x 16 with minimal cup. Starboard prop (a replacement after an ooops!) was a 16 x 15. so I took it to a prop shop to get an inch of pitch added. "No can do," the man told me, but he hammered a heavy cup on the three blades.

Both engines ran identically, with rpm and hole shot similar--I did extensive testing. So 16 x 16 mild cup equals 16 x 15 heavy cup.

Jeff

[zul8tr]

For what its worth.... I had a 32 foot cruiser w/ twin inboards (Mopar 360s). Port prop was a 16 x 16 with minimal cup. Starboard prop (a replacement after an ooops!) was a 16 x 15. so I took it to a prop shop to get an inch of pitch added. "No can do," the man told me, but he hammered a heavy cup on the three blades.

Both engines ran identically, with rpm and hole shot similar--I did extensive testing. So 16 x 16 mild cup equals 16 x 15 heavy cup.

Jeff

He cupped the trailing edge I assume. The discussion is on lead edge cup.

[zul8tr]

Google " Face Cup Boat Racing Facts" .

Tried it as you show it - nada!

How about you find it and post it?

[Fastjeff57]

Correct. Should have noted that.

Jeff

[rumleyfips]

Just tried it and it works for me. You have to use Google, the BRF search is poor. I can email it to you if I get your address.

[zul8tr]

Just tried it and it works for me. You have to use Google, the BRF search is poor. I can email it to you if I get your address.

Found it with Google Chrome straight Google was a nada

http://www.boatracingfacts.com/forums/showthread.php?15002-Face-cup

He discusses exactly what I posted from his web page leading cup or face cup are not correct. He speaks to adjusting leading blade angle for correct entry angle of attack into the water for low drag and great acceleration and top end.

[rumleyfips]

Sorry. I was using Chrome . I didn't know it would make a difference.

[hydrospeed77]

I got a 11.25x18 thru-hub semi-cleaver from Ron that has cupping inwards on the leading edge, only for the last 1/3 of the leading edge before the tip. My initial thoughts were that it didn't look right and that a cavity would be created as it cut through the water. I did hear from a prop lab, when I described it to them, that it does maybe create more "grip". I don't have enough experience to know what that would feel like compared to the same prop without the leading edge cupped inward. Unfortunately haven't had much seat time to do real conclusive testing; only guessing and theorizing at this point...

[filthy phill]

iam thinking of going ahead and doing this to a prop.
I have to test the prop first as it has already had a good few mods that I want to see the results of.
one I do the test of mods I will then go ahead and put a leading edge cup/roll on the blades.

what I am thinking off is something like what I have in this pic, the red line would roughly be the cupped area.

the prop I will use for experiment is not this one, I will try that on a 13x17 sst.

[fs5]

So is this face cup the opposite of doing a Texas cut?
I have a slt boat a good Texas cut prop runs real good . Rons face cup props drag there arse a bit out of the hole and top end. Trimmed the face cup off one and picked up 3 kph and better hole shot ??
If you got the dollars just buy a genuine merc clever can't beat them .

[Ron Hill]

So is this face cup the opposite of doing a Texas cut?
I have a slt boat a good Texas cut prop runs real good . Rons face cup props drag there arse a bit out of the hole and top end. Trimmed the face cup off one and picked up 3 kph and better hole shot ??
If you got the dollars just buy a genuine merc clever can't beat them .

The "Texas Cut" came about from too much "FACE CUP", so we cut some off it and my dad said, "Oh, that's called a 'Texas Cut' but no one in Texas had heard about it."

The first "Texas Cut" I every made was on a Mercury Offshore prop for an SJ.

[hupiveneilija]

SRX on my own . Taken out leading edge cup and trailing edge cup.

[filthy phill]

Sorry but your wording on the parts of the prop is not correct.
On the prop you show above there is added trailing edge cup and added tip cup. a fair amount of tip cup and looks pretty good.
there is no leading edge difference to normal srx.

the work done on your prop would add maybe 1 inch in pitch, and 1/4 inch less diameter . so now about 13.5 x 24..
you might be able to spin that to about 6500 with your new mods to your motor.


The LEADING EDGE is from the bottom of the hub going up to the tip.

as shown in pic below on my srx. the is prop was not altered from new apart from polishing.

[hupiveneilija]

Okay,
Ive bent LEADING edge away from the nut, "derolled" made trailing edge cup SMALLER with TIGHTER cup radius than stock SRX.
Its good You know what Ive done. I dont have to tell that. Yes and also how it works. We have language barrier here, You speak english, I finnish :rolleyes:.
PS. photos do lie

[filthy phill]

yes sometimes the language barrier can be a problem, not only Finnish to English, but even English UK to English USA can also be very different.

but yes I can see you have put a nice cup in the tip, this will lift the bow much better. you have good skill with bending the prop nice.
I need to try this with my srx too.

if I can get the leading edge cupped and the tip cupped on srx it might just be the ideal prop for my boat.
I need more bite from start and a bow lift like a raker prop. but as you know in the uk and Europe no good price props are available, all too expensive.

and yes photo's do lie a lot on computer. I cannot get good picture os my 13x17, it looks realy bad in picture, but in real life it is very nice.