RCProp Tech Info

Gas Prop Tech Notes

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____________RC Props____________

Best viewed at 1600x1200 screen resolution

NEW ABC Proto G-34

Photo from "apache5056". This prop was developed by custom computer generated

imaging software. During a recent conversation with Jim from ABC; re: the 30 series props;

we agreed that, to increase surface drive performance larger Dia. with less Pitch was needed.

The new prototypes will be sold in stock form, the G-34 was made for Mid > High level prop

tweakers, to modify to best suit their own setups. 2.75" Dia is a good starting point. I'd suggest

spooning the blades to create a low lift pushing prop, while maintaining an (aspect ratio)

of about (1.5) depending on the finished Dia. "Powerpete" recently posted on Jims Boat Dock,

his "AM ProCat fitted with a standard 6Hp Mathe 35cc, ran (101 Kph)" = over (65mph).

Paul Govostes Sept. 22nd 2003

Modified Prop Shop 7024/3

Stock @ 70mm Dia x 6.6" Pitch. Modified to 68mm dia x 6.8" average pitch.

Backcut to remove "Lift" & increase "Rake" Spooned Blades and slightly Bent Tips

to "condense" thrust, for increase "push". 7"max pitch @ cup. This is a high pitch, super fast

prop for high powered, or twin engine Cats, Hydros, & Riggers.

_____Photo taken with Nikon D-100 Digital SLR Camera____

RC Props.Com

Octura 1475/2 modified for top speed

The Octura 1475/2 has recently become a hot prop among gas racers and fast runners. It lends it self well to modifications that produce high speed, with many different surface drive applications such as, monos, cats, hydros, and riggers. It comes stock at 2.95"dia x 4.13"pitch, aspect ratio of (1.4). Reducing the dia. to around 70mm and increasing the average pitch to 5.5" and max pitch to about 6.4"including cup, can allow this prop to really turn-on. With the higher aspect ratio of about (1.8). Depending on the setup, with "monos" & "cats", remove lift by back-cut the trailing edge about 1/8th" at the hub, tapering to zero at the tips. A tapered back-cut also increases blade rake. The entire leading edge should be radiused from tip to hub, while removing the tongue. The blade tips should be spooned or concave shape, to add cup, reduce lift, and condense the thrust cone. This redirection of thrust further aft, enables increased forward push with less slip. This increases peak RPM and top SPEED.

Rolling the edge, removes most of, if not all the lift. This causes the transom to be pulled down somewhat, which requires a deep strut setting to keep the nose down. This lower prop setting greatly reduces Slip, which is our single worst enemy. By reducing Slip we increase prop efficiency during it's 360degree revolution, resulting in faster top speed. For best results always thin, sharpen, balance, and polish to a smooth finish.

Paul Govostes 7-24-02

Close-Up (H50-O) 35QD Stryker Cat

H50-O) for 35QD Stryker Cat. This prop is large, at 2.58"Dia. @ 6" max pitch. Ran 74+ mph on a 35QD Stryker Cat and 71mph on the 35QD Hoover Hydro. With the larger Dia, the strut needs to be raised slightly to unload the engine. This lowers ride attitude for more stability in Oval Trim. Note: the well defined Spoon shape blades

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Prop Shop Props

7018/2 7016/2 7016/3

______70 Series PropShop Cleavers (General Use)______

Stock 7018/2 (70mm Dia. x 4.96" Pitch) 7016/2 (70mm Dia. x 4.41" Pitch) 7016/3 (70mm Dia. x 4.41" Pitch) The above three props are ideal with many surface drive gas applications, even in stock form. The 7016/2 is a good choice for pro mod G23 Zen's setup in cats, hydros, and riggers. A little "Back-cut" along the trailing edge, from the hub > tips to remove "lift"; allows this prop to also work well with G23/ monos. The 7016/3 is another good choice for the above setups, however both back-cutting and Dia. reduction to around 68mm is needed for unloading the engine. The 7018/2 with higher 4.96" pitch with the same mods, works great with the above hulls, however the new high powered G23's are needed to pull this prop to max potential. The 7018/3 (same mods) generally requires the stronger 25QuickDraw, 25J&G, and new G260PUM engines. The stock 7020/2 (2.76"Dia x 5.52"Pitch) is a fantastic prop with the (same mods) to reduce "lift" & "dia". The more powerful 25QD & 25J&G's are needed for max speed. The 7020/3 is another Killer Prop for the 35cc QD, J&G, and Mathe' engines, setup in monos, cats, hydros & riggers. Max performance and speed requires sharp edge "Back Cut"/ Spooned Blades/ increased pitched / Dia. slightly reduced to 68mm. The 7022/2, 7022/3, 7024/2, 7024/3...To be continued...

Paul Govostes 9/23/02

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Larger Dia Lower Pitch = Increased Speed

Until recently, I've always gained speed by reducing prop dia. & increasing pitch, allowing higher rpm. However this holds true with gas engines up to a certain point. Gas engines with stock ignitions will only rev so high, then the power drops off dramatically. Most gas engines make peak HP between 12 > 14,000rpm. The smaller dia / higher pitch prop allows the engine to over-rev to 17 > 18000 under load, but at these high rpm's the engine drops to only 1 > 2 HP. Hardly enough to sustain it's speed and In many cases actually slow down. A larger dia - lower pitch prop allows the engine to run faster at a lower rpm, closer to it's normal peak power band ie:(HP) around 15 > 16,000rpm, with less slip. I've gained over 3mph reaching 75 with less pitch larger dia. An electronic ignition is needed to produce higher rpm with increased HP.

How To measure (average blade pitch)

To determine actual (average blade pitch), different measurements must be taken along the blade. With the pitch gauge, I take between 3 >4 measurements; 1st about 1/4'' from the hub,
2nd near the middle, and 3rd near the tips. The tip measurement also determines the pitch of the Cup. Example: 1st = 5" / 2nd = 5.5" / 3rd = 6". The total of the 3 = 16.5" divided by 3 = 5.5". Average Blade Pitch is 5.5", this is the actual distance the prop will travel forward during one 360 degree revolution. Of course Slip is not subtracted from the above measurements.
It is important to calculate average pitch with progressive pitch, or cupped props.

See link (average blade pitch)..... 7020-3 pitch gauge

Paul Govostes 10/21/2002

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Cavitation
____Full Size Subsurface Prop Definition ____

Cavitation (which is often confused with ventilation), is a phenomena

of water vaporizing or "boiling" due to the extreme reduction of pressure

on the back of the propeller blade. Many propellers partially cavitate

during normal operation, but excessive cavitation can result in metal

erosion or "cavitation burn" to the prop's blade surface. There are

numerous causes of cavitation such as incorrect matching of propeller

style to application, incorrect pitch, physical damage to the blade edges, etc.

________________________________________________________________

Note: The above describes typical Cavitation for full size subsurface props.

The Cavitation we experience with RC surface drive props is considerably different.

During launch we have a transition from subsurface to surface drive, as the

boat lifts itself on plane. During this transition, cavitation is considerable, however

diminishes when up on plane at speed. With surface drive the prop blades are partially

submerged and suffer more from "Slippage" then cavitation.

Paul Govostes 10/27/2002

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Increased Pitch / Reduced Lift / Reduced Slip = Faster Speed

" I believe this is very important to understand "

With Surface Drive, you can gain additional speed with most props including the H50, by running it deeper, reducing slip. This is the single best trick for higher speed. In general surface drive props suffer from anywhere between 20 > 35+% Slip. The Speed resulting from High RPM is greatly diminished by excess slippage. The (Spoon Shape) blade narrows the thrust cone as water exits the blades. It is re-directed further aft for increased forward thrust and also reduces lift, as water exiting the submerged blade is also re-directed back. Not straight off the blade in a downward direction. This tends to raise the transom, causing unwanted "Lift".
The trick is to modify the blade shape, to accomplish the above without loading the engine, and lowering RPM! With the (Spoon Shape) Mod you win 3 fold, (Increased Pitch), (Reduced Lift) (Reduced Slip) = Faster Speed.

Paul Govostes Oct. 2003

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Prop Wash Diagram

This diagram shows how the rooster tail is effected, when the strut or drive angle is raised or lowered. It also displays the condensed prop wash, that is a result of a modified (Spooned) prop. A narrow thrust cone causes increased forward push, that results in faster acceleration and top speed. A prop with higher blade rake : (trailing edge of blades are attached to hub at a higher angle, the blades extend further back) This also condenses the thrust cone, as the wash exits the angled back blades. Prop "Lift" is also effected by the above drive angle, rake, and spooned blades.

Paul Govostes Nov. 2002

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________ABC MW 3 & G-20________

New from ABC on left the MW 3 /on right the G-20. Both props are similar to the Octura 1475 and came from the same ABC 75 x 97 mold. The MW3 has a measured. Dia. of ( 2.75") with uneven blade Pitch. While the G-20's (70mm 2.68") measured Dia. is slightly smaller, with 6" average pitch. The G-20 doesn't have the tapered pitch of the MW3 and has less "Lift". It has slightly more pitch; with about the same cup as the MW3. The G-20 also has a slight Barr-Cut along the Leading Edge, starting at the hub and extending out about 1/4". The smaller G-20 is more suited for less powered mono's & cats, while the larger MW3 works best with higher powered 25cc engines. Both props are smooth threw the turns and fast. NOTE: both props & photo from "Fast Props" Chris Hicks.

Paul Govostes 11/18/2002

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________MW 3________

Other view of the new ABC MW 3. Note the slight spoon/concave shape blades and the fairly high blade rake and removed tongue area along the leading edge near the hub. These features increase performance by reducing lift, condensing thrust, and reducing drag. This makes this prop......... FAST.

Paul Govostes 11/21/02

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------------ General Discussion RE: Props ------------

Written By Carlos Eduardo & Paul Govostes

Introduction

When I started thinking about a page like this, I posted some question at Jim's Board; the answers just made me sure that I had a lot to learn. So, when I finished the page I asked Paul G if he could look at it and correct my mistakes. Well, he not only corrected the mistakes but added a lot of great information. It's just a matter of justice register that this is a Carlos / Paul page and I am most honored with such company. Paul, thank your very much for your kindness and for sharing your knowledge with us.

Carlos Eduardo 2/22/02

The page bellow is an attempt to stress the importance of the propeller in r/c boat propulsion. It results from my lectures on the Web and information posted on Jim's board, mainly by Jim Nissen, Paul Govostes and Mike T. When you finish reading this, hopefully you will be interested in learning more. Go to Paul Govostes page:

http://rcprops.com/ He is one of the best on this matter, the only problem is that he doesn’t modify props for sale; you can't buy one of his props, you can only look at them, and dream.

From RC Props: I don't modify or sell props as a business, only as a hobby. I do them for myself, and occasionally for boating friends and racers, free of charge. I will help anyone that (Just Wants To Do It ) by learning the techniques and tricks, needed for tweaking props, for maximum speed!!

---------------The Prop---------------

The prop is responsible for transforming the movement of the motor’s power. It accomplishes this task by displacing a mass of water when turning. One of the first laws of physic states that with each action there is an opposite and equal reaction of the same intensity, and of contrary direction. As a result, the water movement is displaced backwards, and the prop is pushed forward. There is a rigid link to the hull, that results in the boat moving forward in a speed proportional to the volume of water being displaced. The prop rests in the water and moves forward, by the amount of it's pitch – in theory. As water is not a solid mass, the prop slips and the forward movement is less then the theoretical forward motion.

So, the larger the pitch, the higher the speed, as a result of increased forward movement at the same time unit. This is true to a certain point. Sometimes, the pitch is so great, the engine can't reach it's maximum RPM. And less RPM, means less forward movement within the same time unit, = less speed. Compared to your car, a higher gear reaches higher speed – in normal circumstances. On a steep hill for instance, the load on the engine causes a reduction in RPM and a decrease in speed. Under these conditions, the 3^rd gear may be faster. Like the car gear box, smaller pitch has more acceleration and less top speed, while greater pitch has more top speed with less acceleration. (not always true)

Conversely, too little pitch makes the engine over-rev, with possible costly engine damage.

As your boat's engine doesn't have a gear box, the prop has to be carefully chosen to overcome these restrictions.

Diameter is also of prime importance when choosing the right prop: larger diameter = more thrust, and greater capacity for moving a heavy hull. Increasing the pitch generally demands a reduction in diameter, lessening drag and increasing speed. Again, this has a limitation: a minimal diameter is often required to guarantee the necessary thrust.

Moreover, the diameter helps control slippage, larger diameter is less prone to prop slippage, until the larger diameter causes too much drag and reduces engine speed. In a way, diameter directly effects speed, but it's major influence is on water displacement.

The number of blades are also important. The ideal prop should only have one blade, eliminating drag of the other blades that are not producing useful work. Two bladed props are standard with most hulls, on other type hulls, 3 or even 4 blades may be required for additional acceleration and lift. Outriggers and Hydros are the best examples of boats that demand lift at the transom, to ride properly on a 3 point stance.

Blade Thickness (thinner is best). A thin and sharp blade cuts the water and reduces prop-walk tendency (walking to the right as the transom goes to the left, because of the props turning effect).

Preliminary Definitions:

Blade: is the prop part that cuts the water and thrusts it back. In R/C speed boats we use 2 or 3 bladed props, with very few 4 blade props.

Hub: central portion of the prop, where the blades and prop shaft are attached, The Hub provides most of the strength of the propeller.

Diameter: prop size, measured between the tips of the blades. Or 2 times the measurement between the tip of the blade and the center of the hub. Larger diameter props are normally used on large and heavy hulls. With R/C gas boats, 65 to 80 mm is the standard.

Pitch: theoretical distance the prop travels on each rotation. This is theoretical because water is not a solid medium and the prop slips. 10 to 30% is normal, the lower numbers are found only on surface drive hi-performance props, specially prepared.

Constant Pitch: the pitch is the same across the entire propeller’s working surface, or blade face.

.Progressive pitch: the pitch is lower at the leading edge and increases progressively along the trailing edge.

Consider a prop that runs in a liquid media with a constant pitch, the tip of the prop rotates faster than the hub. Conversely, if the angle at the tip is lower, the water speed on all prop surfaces will be the same. In this case, the performance is far better. Progressive pitch props, offer better planning performance.

High lift: a prop which tends to lift the transom when the boat is running.
Low lift: a prop which does not have this tendency.

Aspect ratio (AR): relationship between pitch and diameter, = (pitch divided by diameter). Normally a higher AR means a faster prop. Generally, a faster prop has a higher (AR), more Pitch, with less Dia. However this holds true to a certain extent, as adequate Dia. is necessary to sustained push!

With Octura props, the X series (an X before the number) indicates a low lift prop. Props without the X are high lift props.

Ex.: X470 Octura prop
X= low lift prop.
4= pitch ratio
70= 70 mm diameter

1667 Octura prop
lift prop
1.6 AR
67mm diameter
So: pitch divided by diameter= (AR) or pitch/67=1.6 or pitch=1.6 x 67= 107.2 mm diameter or 4,2"

Cavitation: is water vaporizing due to the extreme reduction of pressure on the back of the propeller blade. Many props partially cavitate during normal operation, but excessive cavitation can result in damage to the prop's blade surface. Note: Cavitation is often confused with Ventilation.

Ventilation: often confused with cavitation, it's normally induced by an external source, not by the prop itself. It occurs when air is directed on the prop surface. Eventually, it may help by reducing cavitation. On real boats, this is sometimes accomplished by directing the exhaust over the prop. On R/C boats this is not a common practice; nevertheless, it looks like some guys from Swiss have tried this. See photo bellow:

Cupping: Is a curvature added at the props trailing edge, normally very slight, towards the blade center, shaped like a spoon. It reduces cavitation and maximize thrust, increasing the effective prop pitch. Additionally, it lifts the bow and narrows the thrust cone. It looks like a magic medicine, the solution for all our problems but, like any medicine, it has to be taken carefully. Besides, cupping has to be equal in all blades, or you will have an imbalanced prop, that may damage your engine.

Camber: Arching curve from leading edge to trailing edge, like a spread out cup. It makes a progressive pitch at the prop.

Rake: Is the angle of the blade attachment to the hub, and the degree that the blades slant forward or backwards. It's normally use to correct ventilation or cavitating situations. Furthermore, rake lifts the bow and so the speed. Typically, low rake props are used on sub-surface drives with heavy hulls. Higher Rake blades with surface drive application, tend to re-direct and condense the thrust cone further aft.

Questions on which prop to use are recurrent at Jim's Board. The selection bellow is a compilation of props indicated.

Manufacturer: not necessarily the manufacturer of the original prop. In some cases, the listed manufacturer is the one who provides the prop modification.

Use: no indication means that the prop was listed as a general purpose prop, one that you should have just in case.

Additional features: additional modifications made to the original prop.

Tips on how to improve your prop: (all posted on Jim's Board)

Carlos:

I found the easiest way to do prop mods is to just do it! Pick up a stock prop you really don't care to ruin. Start by getting it ready to run. Thin and sharp. Then one simple method to do lakeside tests is to make up a bending pliers. Weld a large ball bearing to one jaw of a standard pliers. Smooth out the other jaw so it doesn't have any sharp edges yet is still fairly flat. You would be surprised how little bending will drastically change the props performance.

Remember to bend the trailing edge and blend the bend into the blade so it's a gradual ramp. Once you have something close then you can take it home and clean it up.

How much pitch is OK? You need to measure it. I'll start out by saying I need to get a real prop measuring tool. I built up a dial indicator stand but I am having difficulty getting the setup to measure the same back to back. Paul G. shows a real nice stand on his site. Required if you ever intend to make another one like the one you bent. Keep good records in a notebook on what hull, setup, speed, etc... as this is really critical later on when you get home and try to remember what worked well.

Other notes: I used to use pliers and the ball bearing thing but I also have a prop anvil with three different derlin blocks machined for various blade profiles. Much better blade to blade consistency. Cup can be put into blades rather easily. I have used a small hammer with this setup but they tend to dent the prop back sides. I'm looking for a small rawhide hammer as I hear these are the ticket to prop mods! Just do it. I learned up to this point by ruining several props and making some "junk" props real stars.

Jim Nissen:

Trailing edges should be sharp. Props are like rudders and the sharp trailing edge acts like a wedge rudder's trailing edge. It helps to incorporate air into the trailing edge and this reduces drag from the blade
Paul Govostes:

Hi Jim/ Paul G here,
Great detailed prop post on "Just Do It". However I want to clear-up any possible confusion on trailing edge sharpening. The trailing edge should not be sharpened like the leading edge, it should be done like " a wedge rudder's trailing edge". Here’s a link to a prop pic, that clearly shows what Jim has explained.

Photo by P.P.G.

Paul Govostes:

"NOTE: Marty Davis is referring to water testing a prop with a Dye substance that shows areas of the blade in (RED); that may be removed to increase prop efficiency and performance.

Marty Davis:

"OK...the first thing that you should look for is red along the trailing 1/4 of the prop. If there is any, you have bent the pitch into the prop without a very gradual bend. If you don't have a perfectly gradual bend, it will make areas that will cause cavitation. The second thing to look at is the tongue area of the prop. There will be red in areas of the tongue. That indicates areas that you can remove. The tongue itself will be clean, which shows the opposite, that it is biting to much. The tongue as you know is the lowest pitch part of the prop and it is the thing that holds back the prop (especially on X series props). REMOVE THIS AREA ON X SERIES PROPS and the boat will run much faster.

Mike Tyson

After sharpening and balancing props I run the file across the top edge of the blade to square it up. A round edge will alter the flow of water off the prop, so you want a nice square edge to break the flow cleanly.

:Paul Govostes _____Prop Polishing_____

Generally speaking, a prop that is high polished on both the (anterior & posterior) face & back of the blades, including the hub; will achieve the highest top speed. However there’s some advantage to a rough or less smooth surface, on the "back" of the blade. It gives more bite for short course acceleration, however this can cause drag at higher speeds.
I believe there's little to no difference between a satin finish on the back of the blade, vs. high polish on both sides, until very high speeds are reached.

After reading this, what lessons have you learned? The most important: there is no single prop that is ideal for all possible hull and engine configurations. The basic rules are listed, but consulting the experts and lots of experimentation, documentation, and patience is fundamental.

Best Regards,

Carlos Eduardo / Paul Govostes 2/22/02 Back

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PROP RECOMMENDATIONS

Questions on which prop to use are recurrent at Jim's Board. The selection bellow is a compilation of props indicated.

Manufacturer: not necessarily the manufacturer of the original prop. In some cases, the listed manufacturer is the one who provides the prop modification.

Use: no indication means that the prop was listed as a general purpose prop, one that you should have just in case.

Additional features: additional modifications made to the original prop.

     #                    MANUFACTURE                             USE                                                                       FEATURES

H31

ABC (Paul Govostes)

1. AC Lazer 40 -Prop Comp Motor

1. -

H-50

1. Multi-Use depending on cut shape & pitch

1/3. Cut and pitched, Dia. 2.45 > 2.59",
Pitch 5 > 6.0", Cup > 6.5"max
Spooned Shape Blade/ Lead Cut-Back

2. Stryker Sprint Cyclone Cats etc.

3. 41>50"/ Hydros/ Riggers/ 23>35cc Gas

4. Cyclone cat. modded RC230

4.2.45"Dia x 5.5"Pitch

1667

1. QD25 cat

1. -

1475

Andy Brown

1. Cyclone/ QD 35cc

1. Sharpened & Balanced Cup 7.0"

2. Cyclone/ QD 25cc

2. Sharpened & Balanced, Cup 6.2", cut down to 72mm

3. Apache/ Zenoah

3. Sharpened & Balanced, Cup 6.2"

4. Apache/ J&G

4. Sharpened & Balanced, Cup 6.6"

5. Zenoah gas monos

5. Cut and pitched

6. Seaducer.

6. 6.3" pitch

7. Seaducer2/QD 25 cc

7. Some added pitch

8. RC Boatworks F-41 Stryker cat/QD 25

8/10. -

9. F-41Stryker/Zenoah 230RC mod

10. AC Lazer 40 - Prop Comp motor

11. F-41 Stryker/QD 25

11. mod

12. F-41 Stryker/Zenoah 230RC

12. cut and balanced lift out and pitched

13. 44" Twincraft/Midwest Super Mod G-23

1667

1. RC Boatworks F-41 Stryker cat/QD 25

1. -

2. Cyclone/ QD 25cc

2. Sharpened & Balanced, Cup 6.4"

3. Seaducer2/QD 25 cc

3. Some added pitch

X670

1. Cyclone/ QD 25cc

1. Sharpened & Balanced

7016

1. F-41Stryker/Zenoah 230RC mod

1. Cut and balanced lift out and pitched

2014

English Prop Shop

1. -

1. 3 blades

2016

1. -

1. 3 blades

7014

1. -

1. -

7015

1. Zenoah gas/ cats

1. -

2. Cyclone cat. modded RC230

2.Dia reduced to 68mm / Pitch increased to 5.5" @ Cup.

7015/3

1. Cyclone cat. modded RC230

1. -

7016

1. General

1. -

2. Cyclone cat. modded RC230

2. Star-cut mod.

3. 44" Twincraft/Midwest Super Mod G-23

7018/2

1. Stryker Cat/ QD 25

1. -

P967

Octura

1. AC Lazer 40" – Pro comp motor

1. Sharpened and balanced

1475

1. -

1. Couple of AB,s with different mods

2. -

2. Several cut and pitched

3. F-41Stryker/Zenoah G-23 mod

3. -

1667/2

1. -

1. Cut down and pitched somewhat like the 1475's

7016

1. F-41 Stryker/mid mod Zenoah   mod

1. -

7016/3/4

1. -

1. A good and sharp with mods

7018/2/3

1. -

1. A good and sharp with mods

7018/3

1. F-41 Stryker/mid mod Zenoah

1. -

2. Mono 48 QD35

2. -

7020

1. F-41 Stryker/mid mod Zenoah   mod

1/3. -

2. F-41 Stryker/QD

3. QD25 cat

7020/2/3

1. -

1. A good and sharp with mods

2. Mono 48 QD35

2. back-cut the trailing edge

X470

1. Zenoah engine

1/2 -

2. Crackerbox + surface drive

X470/3

1. F-41 Stryker

1/2. -

2. AC Lazer 40" – Pro comp motor

X472

1. F-41 Stryker/mid mod Zenoah

1/9 -

2. AC Lazer 40" – Pro comp motor

3. Apache/stock Homelite 25cc

4. Zenoah engine

5.Homeliteengine

6. Cat 43"/Homelite

7. Homelite engine

8. QD25 cat

9. 44" Twincraft/Midwest
Super Mod G-23

X482

1. -

1. good and sharp BC and cut down

2. Mono 46/JT Mod 25cc Homie

2. -

3. 44" Twincraft/Midwest
Super Mod G-23

3. trimmed.

X570

1. -

1. -

X572

1. -

1. Good and sharp and mods

2. Cat 43"/Homelite

2. -

X670

1. -

1. -

2. Seaducer

2/3. -

3. Stryker Cat/QD 25

275

Prather

1. -

1. A good and sharp S/Steel

2. -

2. SS, cut down some

3. -

3. Bronze, stock

4. Crackerbox

4/6. -

5. Challenger 48

6. Homelite engine

7. Crackerbox + surface drive

7. much modified Homelite 25 cc surface drive

8. Cat 43"/Homelite

8/13. -

9. RC Boatworks F-41 Stryker cat/QD 25

10. Apache/stock Homelite 25

11. Homelite engine

12. Mono 46 JT Mod 25cc Homie

13. QD25 cat

280

1. RC Boatworks F-41 Stryker cat/QD 252

1/2. -

2. Zenoah engine

3. -

3. Bronze, stock

4. -

4. SS, cut down some

5. Cat 43"/Homelite

5. Sharpened and balanced

7015/3

Prop Shop

1. -

1. Cut down and pitched somewhat like the 1475's

7016

1. QD25 cat

1. -

7016/2

1. General

1/2. -

2. Zenoah engine

3. Cat 43"/Homelite

3. Back-Cut & tweaked

7016/3

1. Zenoah engine

1. Zen-Cats best friend

7018

1. -

1. Cut down and pitched somewhat like the 1475's

2. Cat 43"/Homelite

2. Back-Cut & tweaked

3. Cat 43"/Homelite

3. Back-Cut & tweaked

4. RC Boatworks F-41 Stryker cat/QD 25

4. For heat racing

5. QD25 cat

5. -

7018/3

1. Cat 43"/Homelite

1. Back-Cut & tweaked

1475

RR Prop Shop

1. -

1. Specially cupped by Andy Brown

6520

1. Stryker

1. -

6520/3

7015

7016

7016/3

7018

7018/3

767/3

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________Prop Polishing More Speed________

Generally speaking, props that are high polished on both the face & back, including the hub; will achieve the highest top speed. However there is some advantage to a rough or less smooth surface, on
the (back) of the blade area. It gives more bite for short course acceleration, however can cause drag at higher speeds. There's little to no difference between a satin finish on the back of the blade vs.high polish on both sides, until (very high speeds) are reached. I've tested the above polished vs satin props on the same boat, back to back. Satin = 72mph and polished = 72.4mph. You can draw your own conclusions weather it's worth polishing your props, however I polish mine for max speed potential.

Example: (Mod H50) for 35QD-Stryker Cat

Satin Finish on the Face of the blade, provides improved low end bite, for quicker acceleration! However, I believe this finish reduces top speed at very high RPM. For best SAW performance, both sides of the blade should be smooth, with a polished finish. (2.50" Dia. x 6.2" Pitch)

Paul Govostes 1/8/2002
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________ Should Both Sides of the Blade be Polished?_______

Should both anterior & posterior facing surfaces need polishing"? There are conflicting opinions RE: this subject. Some say / never polish the BACK of the blade; as this is the push area and should be left untouched. And somewhat ruff to allow for more bite, for the prop to dig-in with less slip. I agree with the above, only when operating at lower RPM!! With today's surface drive applications and high RPM; it is vital that both sides (Back & Face) of the prop blades, be polished! The entire surface of the prop should be as smooth as possible, to reduce drag and increase efficiency. Props that are thin and sharp, with (both sides of the blades polished); pierce, and flow thru the water with less resistance. A slippery prop is a fast prop........!!!! However when heat racing in a short oval course, there is some advantage in keeping the back side of the blade somewhat coarse. This allows quick acceleration, and helps pop the boat, while pulling out of the turns.

Paul Govostes 1/21/2001

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________The Relationship Between Pitch and Diameter (Aspect Ratio)________

The relationship between pitch and diameter, is measured as the "Aspect Ratio. (Pitch divided byDia) (e.g.) The Octura 1475 has 4.13"Pitch/ 2.95"Dia. The relationship between Pitch 4.13"divided by Dia 2.95" = (1.4 Aspect Ratio). Higher Aspect Ratio = More Pitch/ Less Dia. And lower (AR) = Less Pitch/ More Dia. Generally, a faster prop has a higher (AR), more Pitch, with less Dia. However this holds true to a certain extent, as adequate Dia. is necessary to sustained push!

Paul Govostes 12/23/2001 ____________________________________________________________________________ Back

________Details: Bending The Tips Of The H-50________

The prop blades must first be thinned and trimmed. Roll the tips in towards the hub.
Place the blade over a hard nylon or plastic (Dome) with the tip extending
about 1/8th" over the top of dome. Using a sm. raw hide hammer, tap the
blade tip area until it takes the concave shape of the rounded dome. Do the
exact same to the other blade. This will reduce the Dia and Lift, without
removing blade surface!! This is the real trick in modifying H-50's & many
other props. It condenses & redirects the thrust cone aft for increased forward push,
with much less lift! Now the strut can be lowered to run the prop deeper,
which removes much of the slip that you get with a high strut, without loading the engine.

Paul Govostes 8/10/2000

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Increasing Blade Pitch

There are several different ways to increase blade pitch. The easiest and often most effective approach is to start your bend about 1/4>3/8th" below the (Trailing Edge), at a point about 60>70% out from the Hub. Gradually bend to end in with a smooth increased blade ramp, than re-measure your pitch. The blade should be bent at 2>3 different points, while gently adding pitch. Always re-measure between bends. I also bend or contour the (leading Edge) to add or remove pitch at the lead. I don't recommend bending the leading edge, unless you’re experienced with leading edge re-shaping. This is where you can screw-up a prop, very easily.

RE: Rake; a higher blade rake does help to redirect and condense the thrust cone. Deep Back-Cutting, starting at the Hub along the trailing edge, tapering to Zero at the tip; will increase Rake. However, if your main goal is high Rake, it's best to start with a high Rake Prop. Rake isn't that important with our surface-drive boats. It's very important with (full size), sub-surface race boats, because all blade surfaces are submerged.

Paul Govostes 6/25/04

________Which Prop: for a Peanut G23/Sprint or Stryker Cat________

The 7016/3 that I modified actually ran the oval course very well, on the Pro-Mod MidWest G-23/Stryker. It pulled pretty strong threw the turns and got up to speed quickly. Please note, it doesn't perform as good as a X470 or 472 in heat racing, however it can be 10>>12mph faster down the straight... The strut has to be raised to almost 1/2" above the sponsons, with a positive angle, to unload the motor and allow the cat to "Hang". I did a lot of Mods on this 7016/3 prop. Extreme and Back-Cut, Reduced Dia.>from 2.76" >>2.68" and slightly bent the tips to increase pitch, reduce lift, redirect the thrust cone future back. The stock 7016/3 is to much prop for heat racing, it needs the above mods. The ABC S30/4 is a great short course prop for this setup, unloads very quickly, but after 50ft or so, you run out of prop and Max-out your speed....!!!

The absolute best all-around prop for this setup is the ABC H-50, but in stock form it won't work well at all. Needs to be greatly modified, >Dia reduced from 2.56">>2.45" with max pitch about 5.5". Spoon shaped the blades to reduce lift & narrow the thrust cone / 1/4" Barr-Cut Notch near hub, along trailing edge, to unload the motor etc............!!!!!!!! I've hit over 63mph on radar with a little H-50 and pulled threw turns like on rails......!!! Also The Octura P767/3 cut down to about 65mm does very well. The ABC H49, stock at 2.47" Dia. with 5.5" Pitch; looks real good for a Peanut G23/Cat.

Paul Govostes 9/18/2001 __________________________________________________

______Subject: Prop Info 4/1/00 Response To Prop Question______

1st question "How to Texas Cut" This is a term that is often used, and commonly misunderstood.
A simple Texas-Cut, is sharpening the leading edge/ > More specific/ > Remove blade material along the leading edge/ > Contour or cut-back the leading edge, from the blade tip > hub. Instead of a gradual blend in the leading edge, cut it at a straight angle from the hub. This reduces the overall size and Dia. of the prop. without removing pitch! This generally improves prop efficiency, and helps to un-load the motor; while not greatly changing the Aspect-Ratio > Pitch divided by Dia.

Paul Govostes

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______2nd question "Difference Between Pointed and Rounded Blade Tips"______

A pointed, or sharp blade tip, generally is known as a Star cut tip/ which is used for most surface-piercing/ surface-drive applications. The star cut tips allow water to exit the blade/ straight-off!! thus throwing the wash in an upward direction when that blade is rotating out of the water. However, the submerged blade is throwing wash in a downward direction, which tends to LIFT the transom. As a rule of thumb/ star cut tips, generally are lifting props. However there are other factors, such as tapered pitch/ Rake/ and Flow threw ventilating, that effect LIFT characteristics. The rounded shape blade tends to redirect the wash/ Thrust Cone/ further back >Less Lift, more forward thrust. In closing: For best prop performance; sharpen to near razor edge, balance as well as possible, and polish so ALL surfaces are as slick as possible.
Paul Govostes 4/1/2000

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______The Benefits of Removing the Tongue Area of a Prop______

Removing the tongue will reduce lift and increase low end rpm's. By removing the leading edge tongue area, it's more likely to slip at the low rpm launch, however at higher rpm and speed the tongue causes drag. Because the centrifugal force of the rotating prop at speed, throws the water away from the hub and tongue, towards the outer surface of the blades. This is why removing the tongue, generally increases rpm and top speed. I think this is important to understand. Also the tongue area has the lowest amount of pitch, which also adds drag at high rpm.

Paul Govostes 10/21/2002

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PROP SHARPENING and BALANCING__

You don't need a fancy balancer, just one that works well enough to detected if one blade is heaver. IE: The heaver blade will hang lower, and the balance doesn't have to be perfect. The main thing is to mark your blades or number them and work the heavy one first. 3 blade props are much more difficult to balance then 2 or 4 bladed props, because each blade is 135degrees apart. Not directly opposite, as a 2 blade that's 180degrees apart. For balancing, a 4 blade is the same as a 2 blade, with 2 blades directly opposite from each other. A 5 blade is difficult, (same reason) as the 3 blade.

Never touch the back of the blades; (the concave side). Work the face of the blade, along the leading edge; from the tongue area near the hub, to the tips. It's better to use small files and fine grade sandpaper, then to use a dremel. Work the blades, as sharp and as smooth as possible. See link 7020/3 on perfect balance a photo of my simple prop balancer. Note: a prop that spins and the blades never stop in the same position, is perfectly balanced. A prop that always stops with it's blades horizontal with the hub same side down, is heavy on that side of the hub.

Paul Govostes 4/9/04

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General Prop. Modification

The cleaver shape is similar to the Prop Shop's blade shape. The leading edge does not curve forward and then blend back with rounded "tongues". Rather it blends into the trailing edge from the hub gradually down the blade. A Texas Cut could also be tried. Instead of a gradual blend in the leading edge, cut it at a straight angle from the hub. Some of the H series ABC props used this technique. In both cases you are eliminating the lower pitched parts of the prop tongues and providing a large surface area for the prop to first pierce the water. I find that Back and Barr cutting along the leading edge, with elimination of the tongues and pitching up the blade provides good results. Your results may vary! The real trick is to be able to read the rooster tail and determine if your hull rides well with a particular cut. I can do this with Mono's and Cats fairly well, but the Hydro and Rigger are more difficult as you need to provide some lift for proper ride attitude.

Paul Govostes 6/20/02

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(Loading the Prop) Good or Bad?

Using a prop with different blade pitch for faster speed, is an old Nitro trick called "LOADING The PROP". The higher pitch blade is positioned to coincide with the (Engine Power-Stroke). I believe this doesn't work; it actually can slow the boat down! A prop with different pitched blades has an
average pitch of both the lower and higher pitch. Example, if one blade has 5" pitch, and the other 5.5" pitch, the actual pitch of the prop is 5.25", the uneven blade pitch cancels each other out. The lower pitch blade can act as drag during the 360 degree revolution of the prop.

Paul Govostes 6/20/06

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