prop cup. do these pics look correct?

I have made a die to cup props.(I hope) I was looking for a tip or 2 on weather or not I am on the right track. the bend is 1/8" deep from the exit edge and has an even transition to the original blade form. the bend starts at 2/3 from the hub and the tip is about 6.5 degrees. If I am WAY off, be kind... you were a newbie once too.

SORRY!!!!!! PICS TOO BIG! didnt mean to waste so much space...... :unsure:

Steve,

What you have their is a little tip pitch. To get cup, you need to bend the

trailing edge up a little, at 70% up the trailing edge. I hope you have a

pitch gauge, because you will need to measure the cup that you put into

the blade, so you can be accurate. For cupping, I use a special pair of

cupping pliers and a propeller holder, so I can get the very edge of the

trailing edge.

Good Luck,

Mark Sholund

shoboat said:

Steve,
What you have their is a little tip pitch. To get cup, you need to bend the

trailing edge up a little, at 70% up the trailing edge. I hope you have a

pitch gauge, because you will need to measure the cup that you put into

the blade, so you can be accurate. For cupping, I use a special pair of

cupping pliers and a propeller holder, so I can get the very edge of the

trailing edge.

Good Luck,

Mark Sholund

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Hey Mark,

I could use a little help with the terminology.

TE or trailing edge =

LE or leading edge =

Cup vers. Pitch =

Any help from anyone is appreciated.

-Buck-

Steve,

What you have done is increased the rake angle at the tip. This will mainly reducuce lift and sometimes reduce cavitation. This "cup" that you have added to the tip will not change the average pitch of the prop much, if at all.

The best way to learn, is to go to the pond and make changes and see how they effect the boat.

After 30 years of experimenting, you will be an "Ex-spurt" like me!

Buck,

You have the terminology down pat, L.E. = Leading Edge(front of the blade)

T.E. = Trailing Edge(Back of the Blade) P.P.=Pitch Progression( %)

Pitch is measured many different ways,but the most common on our propellers

is the average pitch thoughout the blade. Cup is really just the last little angle

before the trailing edge. If you like to think of it another way, think of the face

of the propeller is like a ski jump. The end of the jump would be the cup angle.

It is usually measured at 70% out from the hub/bore of the propeller. You need

a pitch gauge to measure this area accurately,because a little too much cup in

the T.E. and you can really slow a boat down considerably. Remember cup does

a few things to the propeller,it redirects the water off of the T.E. and it does

slow down RPM of the motor and pipe combination. The next fun one to learn

about is P.P. = Pitch Progression it is the difference between the L.E. and the

T.E. and it is measured in a percentage (%) with 40% great for Hydros and

60% or less for Monos. The lower the % of P.P. you have, the faster you will

go. One other thing on the cupping, it also changes the Thrust Cone of the water

leaving the face of the propeller. This is why you can get an increase in speed

to a point, when you cup the T.E. just a little bit. If you want to go faster try

modifying the L.E. of the propeller, so you can lower the P.P. %. This is how to

get your set up right on,but it does take a few trips to the pond to learn how

your modifications affect the performance of your boat. I am heading their right

now to see how my latest batch is working. :lol:

Schools Over For The Day, :lol: :lol: :lol:

Keep Testing,

Mark Sholund

Thanks Mark

-Buck-

AndyBrown said:

Steve,
What you have done is increased the rake angle at the tip.  This will mainly reducuce lift and sometimes reduce cavitation.  This "cup" that you have added to the tip will not change the average pitch of the prop much, if at all.

The best way to learn, is to go to the pond and make changes and see how they effect the boat.

After 30 years of experimenting, you will be an "Ex-spurt"  like me! 

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Andy,

thanks for the advise,

so let me get this straight.... I need to bend the concave side in more. (adding more to the curvature of the blade) this should be done at approximatley 2/3 (66%) or 70% as mark mentioned, from the hub. So 1/3 of the blade should be bent inward (to increase the curvature) to a certain amount of degrees. (the degrees are measured with a pitch gage).

with this done, I should increase the amount of "cup" until the motor can not push it (faster) anymore.

With the bend I have shown in the pics, do any thing other than reduce lift? I assume "lift" is how high the nose of the boat sits while on plane.

I have read the thread on the radar guns, and will get a better one than the one I had. ( before it died, I got my TS2 up to 46 MPH). The testing JD did on my first props shown 32 MPH. I duplicated that reading with another prop, but with only altering the surface condition, I picked up 14 MPH. I have proven, and hope people take note,..........shiny is slow

Steve

Steve,

Correct me if I'm wrong,but I don't think shiny vs satin is worth 14 MPH.

We have got the TS-2 up over 50 MPH with a O.S. motor and a X-440

propeller, that we reduced a little 38.61mm and reduced the cup to 3.46".

If you did another propeller for your TS-2 it must have had either a different

cup and/or diameter to gain 14 MPH. I work all summer long to try and gain

5 MPH on my 21 Hydros,14 MPH on a 21 Tunnel is a huge gain. They will not

come up too fast now,(MPH) as you are getting to the point where it is hard

to go much faster with a stock motor on a tunnel hull.

Keep Testing,

Mark Sholund

When I talk about gaining or reducing lift, I always speak in terms of what is happening at the prop. Reducing prop lift, will normally (but not always) raise the bow of the boat.

I normally cup the full T.E. Of course, the closer you get to the hub, the less you can add. I take measurements at 50% and 70% out from the hub.

Only bring the cup around the tip if you need to reduce some prop lift. Cupping the L.E. will reduce prop lift and reduce pitch. Adding pitch to the L.E. can only be done to certain props with good results. Doing this will add prop lift and it doesn't take much to ruin a good prop when working with the L.E.

Matt finish is faster and with some prop/boat combo's the difference can be significant.

If you can get a addition 14 mph on a prop. i will send you all of mine lol..

I know how tuff it is.. like mark and andy said. working and testing is the only way.

you can talk to ten people and get ten different anwsers but what works for one doesn't always work for another.

Have you tried anything other than what you normaly run??

just keep working with them. you will screw up a bunch before you finally get what you are looking for..

trust me my fingers still hurt lol!!!!!

chris

Speaking of trying something you don't normally run...... howzabout this??

I've been trying to find the "killer 20 mono prop" for awhile, and here's how I came about the inspiration for my latest experiment...

A few years back when I was still actively racing, I tried a 1457/3 on the back of my 80 mono. Didn't modify it much, just a little tip pitch and rolled over the outside like what you done here to decrease the lift. Proved to be the best performing prop for that boat... if I knew then what I know now... I wasn't even close to that prop's potential... So I knew that with a little effort, 1400 series props could work well on a mono... file that away for reference...

My 20 mono at the time was a K&B powered AC hull. I tried an ABC 40X62/3 on it.... Welll... it cavitated terribly on launch... but lo and behold the bleepin thing hooked up... and that boat ran faster than it ever did... much faster in fact... Figured I couldn't risk running it on race day due to the cavitation, but there was something there that needed to be found out......A while later I got a decent pitch gauge, and I pulled that prop back out... the light bulb's getting brighter......

This spring I cut down a few larger X-blades to 40mm and a 70% progression... and the 448 I did seemed to work the best there.. But I still wasn't seeing what I thought I should be....Was thinking to myself if Octura made a 1442/3.... Going through my prop box I stuck an old plastic 1200 series prop on my pitch gauge... and that LE surprised the @#% out of me.. Octura has a 1240/3 in beryllium, and I figured that might be something worth looking at... Got one from Gary Preusse, and the first thing I checked was the LE... 1.88...good!! Problem was the rest of the prop measured that too!!

What I wound up doing, I brought that ABC prop back out, picked a blade that measured where I wanted it (all 3 were different...) and made myself a series of prop duplicators... All said and done I now have a 1240/3 that I'm itching to try... If the formulas run true i may have a 53mph mono??!! its to be seen...

shoboat said:

Steve,
Correct me if I'm wrong,but I don't think shiny vs satin is worth 14 MPH.

We have got the TS-2 up over 50 MPH with a O.S. motor and a X-440

propeller, that we reduced a little 38.61mm and reduced the cup to 3.46".

If you did another propeller for your TS-2 it must have had either a different

cup and/or diameter to gain 14 MPH. I work all summer long to try and gain

5 MPH on my 21 Hydros,14 MPH on a 21 Tunnel is a huge gain. They will not

come up too fast now,(MPH) as you are getting to the point where it is hard

to go much faster with a stock motor on a tunnel hull.

Keep Testing,

Mark Sholund

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Mark,

You are correct. The tested props were x440's. The Prop I matted was a 215. <_< <_< Here I thought I did something spectacular

My appologies for blowing smoke up your pipe

When I listen you guys talk about all this technical prop stuff I feel like a kid watching the space shuttle launch....It looks cool, but there is much more to it than is visable at first.

28 more years to go....Then I'll make a super-duper prop.

sweet

jason <_<