Please advise on prop. Selection an desired WOT RPM

[the brain]

Please advise on prop. Selection an desired WOT RPM for a 2012 ETEC 175HP gen1.I believe 5850 (consulting experts bc I'm not sure.) is desired RPM so I'm currently leaving a few RPMs on the table.


200 /300RPM Discrepancy between WOT tacks. I think the Ray Marine is more accurate (which is higher) getting signal from EMM. or could OMC an Ray both interfer w/ each other?

Still image:
5500RPM at 41MPH OEM tack 5200 RPM trimed up so I'm leaving 350RPM on the table?


still image:Ray 4900 40MPH good water presure OEM tack 4700


video rear shot:

video rear shot moving alone good

moving along nicely is a fast cruise of 37MPH





video: engine shot: cav plate marked in pink, sking good trimmed down cav plate sking even higher w/ trimmed up so I think engine height is fine. note the pink marked tape started to peel off a bit creating some tabulate water.

Video see pink cav plate when trimmed up

Video link








video full throttle out the hole trimmed in/down RPM up to 6K bogged down but still got on plate just a tad slower image

then video

full throttle out the hole trimmed in bogged down RPM up to 6K

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vessel is 1977 Starcraft Lake cruiser 22' w/ 24” setback engine pod

hull weight 1950LB by todays standards it would be classified as multi species type hull big aluminum hull.

2012 Evinrude ETEC 175HP 418LBs so basicely a litish vessel. Tests done w/ minimal gear.

A normal cruise add 50 gallons of fuel, 200LBs of gear.


prop. Being tested was OMC 391201 14.5x19 3-Blade RH w/ decent cupping, aluminum

seamed like lose of traction out the hole full throttle unknown why.



I'd like a tad bit more top end speed maybe 10MPH. Besides flooring it out the hole she'll usalley planes very quickly like if above 1500RPM (basicley moving slowly) then flooring instant on plane so bottom end seams good.

Please advise for a tad bit more top end speed

w/out scarificeing to much low end. thanks

 

[HelmutSheina]

That prop has cavitation burns towards the blade tips and there appears to be some damage on the prop that may be doing it. WOT RPM is 5850 like you said, so you could try a 17 or 18 pitch Al or a 16 or 17 stainless to raise RPM. Going up to 6000 would be acceptable, just don't run it there all day.

On the tach discrepancy, pick one to follow and forget the other, either one, or both of them, are slightly inaccurate. Gauges are a PITA for marine mechanics. You can buy a 3rd party tach to check it, but how accurate or precise will that be?

I'm not having the best day and your post was quite long. Did I miss anything?

 

[HelmutSheina]

On the cavvy burns, they can be dangerous and cause a blade to break off if they're at the root, but yours are further out towards the tip.

They are caused by vacuum pockets in the water collapsing against the prop. It will be either something jagged on the prop, or something further forward underneath the boat.

They do not cause many performance problems, but wreck prop eventually.

I put a mark around them, but it's a finger on a phone screen, pretty rough.

 

[baeckmo]

Cavitation marks on the pressure side of the blade indicates leading edge is operating with negative angle of attack, ie slightly low pitch. Cavities collapse when hitting cup edge due to pressure increase. Note that the E-tech engines have a flat power curve with constant max power delivered from under 5000 rpms and up. Thus there is nothing to gain by operating this engine at screaming rpms.

 

[the brain]

That prop has cavitation burns towards the blade tips and there appears to be some damage on the prop that may be doing it. WOT RPM is 5850 like you said, so you could try a 17 or 18 pitch Al or a 16 or 17 stainless to raise RPM. Going up to 6000 would be acceptable, just don't run it there all day.

On the tach discrepancy, pick one to follow and forget the other, either one, or both of them, are slightly inaccurate. Gauges are a PITA for marine mechanics. You can buy a 3rd party tach to check it, but how accurate or precise will that be?

I'm not having the best day and your post was quite long. Did I miss anything?

HelmutSheina hope your feeling better today. the cavitation burns you mention where actuely pointed out to me on another forum. I was instructed to litely file the tiny nicks out. here

this image was the for sale image. I have since litely filed. are you saying the flat section where the paint has been blasted off needs smoothing? please advise on refurbing whats left of this prop. an thanks

here's a few props I'm considering

https://www.ebay.com/itm/127749674008?boolp=5&ul_noapp=true

I believe I can reuse my ETECs prop shaft selve w/ this ebay prop.?
my sleeve

heres 2nd choice which mite be to damaged

https://www.ebay.com/itm/236811667175?_trkparms=amclksrc%3DITM%26aid%3D777008%26algo%3DPERSONAL.TOPIC%26ao%3D1%26asc%3D20250417133222%26meid%3Dbec4b63393fc4b5699bcd1b4d91bae66%26pid%3D102727%26rk%3D1%26rkt%3D1%26mehot%3Dnone%26itm%3D236811667175%26pmt%3D0%26noa%3D1%26pg%3D4375194%26algv%3DWatchlistVariantWithPSItemDR_BP&_trksid=p4375194.c102727.m162921

or this brand new aluminum not sure if it's thrust washer can be use in saltwater an how long the rubber sleeve will last for.

Amazon.com : Evinrude/Johnson/OMC New OEM Prop 14.5 (1/2) x19 Propeller 765188 (763468) Cobra : Boat Propellers : Sports & Outdoors

Amazon.com : Evinrude/Johnson/OMC New OEM Prop 14.5 (1/2) x19 Propeller 765188 (763468) Cobra : Boat Propellers : Sports & Outdoors

www.amazon.com

thanks for advising

 

[the brain]

Cavitation marks on the pressure side of the blade indicates leading edge is operating with negative angle of attack, ie slightly low pitch. Cavities collapse when hitting cup edge due to pressure increase. Note that the E-tech engines have a flat power curve with constant max power delivered from under 5000 rpms and up. Thus there is nothing to gain by operating this engine at screaming rpms.

​

baeckmo​

are you saying I should lower my wide open throttle from 5850RPM during my testing?​

and I can increase pitch to 20"
thanks for advising

​

 

[jehardiman]

Note that the E-tech engines have a flat power curve with constant max power delivered from under 5000 rpms and up. Thus there is nothing to gain by operating this engine at screaming rpms.

are you saying I should lower my wide open throttle from 5850RPM during my testing?

What he is saying is that the engine delivers no additional Hp past 5000 RPM, i.e. torque*rpm/(a constant) = shaft Hp (SHP) . The boat absorbs Hp as: drag*speed/(a constant)= effective Hp (EHP). Once effective Hp (EHP) = delivered Hp (SHP) your speed will not increase, you will only flog the engine.

Often ICE's have a maximum delivered power (SHP) at less than max RPM; the trick is to find the RPM for max power and design the prop for that power and speed....and that requires knowing the speed where EHP = SHP.

See this post:

Post in thread 'Propeller Efficiency'

Mar 16, 2005

Pardon me if this is long and been said else where better.

First, propellers are usualy describe by three critical factors. The advance coefficient (J) which is a function of the propeller advance (Va), diameter (D) and the RPS (n): J=Va/Dn. The Torque coefficient curve (Kq), a function of torque (Q) at a given J and water density (rho): Kq=Q/(rho*n^2*D^5). And the Thrust coefficient curve (Kt), a function of thrust (T) at a given J and water density: Kt=T/(rho*n^2*D^4). the "open water" efficency (eta O) of a propeller is a measure of the ability of the prop to turn torque into thrust...

• jehardiman

 

[DogCavalry]

If you are losing grip accelerating hard coming up up onto plane, your prop can't accept that much power. Disk loading is too high. Increase prop diameter, before increasing pitch. That o/b leg can take a 16" prop. Don't go that extreme though. Causes vibration when the induced flow off the blade tip meets the AV plate.

Another 10mph when you are already getting 40 is a big jump, not "a tad"

 

[the brain]

What he is saying is that the engine delivers no additional Hp past 5000 RPM, i.e. torque*rpm/(a constant) = shaft Hp (SHP) . The boat absorbs Hp as: drag*speed/(a constant)= effective Hp (EHP). Once effective Hp (EHP) = delivered Hp (SHP) your speed will not increase, you will only flog the engine.

Often ICE's have a maximum delivered power (SHP) at less than max RPM; the trick is to find the RPM for max power and design the prop for that power and speed....and that requires knowing the speed where EHP = SHP.

See this post:

Post in thread 'Propeller Efficiency'

Mar 16, 2005

Pardon me if this is long and been said else where better.

First, propellers are usualy describe by three critical factors. The advance coefficient (J) which is a function of the propeller advance (Va), diameter (D) and the RPS (n): J=Va/Dn. The Torque coefficient curve (Kq), a function of torque (Q) at a given J and water density (rho): Kq=Q/(rho*n^2*D^5). And the Thrust coefficient curve (Kt), a function of thrust (T) at a given J and water density: Kt=T/(rho*n^2*D^4). the "open water" efficency (eta O) of a propeller is a measure of the ability of the prop to turn torque into thrust...

• jehardiman

OK I'm learning more about prop.s thanks Jehardiman for explaining. when I did these shakedown runs I keep the engine trimmed in for most part untill speed stopped increasing then I trimmed up an observed a few more MPH.

yesterday when I consulted the internet bot AI after it crunched my #s it said I have 26% slip I responded it that excessive, it said yes you should have 10%. so I'm now concerned the current prop.s bushing is detaching from the prop. (spun prop.).

here is a summary bots explaination
Bots explaination after crunching my shakedown runs #sThe Math Breakdown (Why 10%+ Isn't Possible)• Current Performance Profile: At 5,800 RPM with a 1.86:1 gear ratio and a 19-pitch prop, your theoretical speed (assuming 0% slip) is 56.1 mph
• bot presumes: High Slip Reality: Because your actual top speed is 41.2 mph, your hull is currently running at a 26.5% prop slip rate. This indicates your boat is likely a heavier fiberglass hull, a pontoon, or has the motor mounted too low on the transom bot explains Stainless steel less slip:Stainless Steel Reality: Upgrading from aluminum toa basic stainless steel prop (like an Evinrude Viper or SST) typically reduces slip by 3% to 5%due to less blade flexing under load.

• The Expected Gain: Dropping your slip from 26.5% to roughly 22% will bring your top speed up to about 43.5 mph. That is a realistic 5% increase (roughly 2.3 mph)—not 10%.

I ask• is 26% slip excesiveJuly 26, 2026
Yes, 26% prop slip is highly excessive for a standard planing hull. A well-optimized boat setup typically has a slip percentage between 10% and 15%

• A 26% slip rate means your aluminum propeller is wasting over a quarter of its energy churning water instead of moving the boat forward What is Causing Your High Slip?

• Aluminum Blade Flex: Aluminum is a soft metal. At 5,800 RPM, your propeller blades are literally bending and flattening out under the pressure, losing their grip on the water.

• Engine Mounted Too Low: This is the most common culprit. If your motor is bolted too deep on the transom, the gearcase creates massive hydrodynamic drag, forcing the prop to operate in highly turbulent water. I 've disproven this w/ cav plate sking on surface.

• Wrong Propeller Geometry: Your current propeller may lack "cupping" (the curved trailing edge of a blade), or it may not have enough surface area to carry your boat's weight efficiently.

I can say this current prop has twice the cupping of previous props. I've had

bots suggestion to reduce slipThe Fix: Drop Slip to 12%If you fix this slip issue on your current 175hp motor by switching to a cupped Stainless Steelprop and raising your engine 1 or 2 holes, your slip will drop to a normal 12%.Mathematically, dropping your slip to 12% at 5,800 RPM will instantly jump your top speed from 41.2 mph to 49.3 mph without adding a single horsepower.Now this 49.3MPH would be satisfactory so it sounds like I need a stronger prop. Sleeve bushing that won't separate like rubber.The ETEC viper has such a bushing I post image above.

I have links above on prospective props.
final prop. maybe

https://www.ebay.com/itm/127749674008?boolp=5&ul_noapp=true

thanks for advise

 

[the brain]

If you are losing grip accelerating hard coming up up onto plane, your prop can't accept that much power. Disk loading is too high. Increase prop diameter, before increasing pitch. That o/b leg can take a 16" prop. Don't go that extreme though. Causes vibration when the induced flow off the blade tip meets the AV plate.

Another 10mph when you are already getting 40 is a big jump, not "a tad"

to clairify when I floored her an the prop was spinning but vessel wasn't moving much basicley churning an RPM shoot up to just over 6K RPM that was at rest. if I'm moving say 5MPH then floor it she takes off basicely instantly on plane.

I'm not sure if this is factorial or false but I've read the small block 2.6litre ETECs 130HP /200HP actuely prefer a 14.25 diameter prop. they where explaining the ETEC like to spin faster thus the slitely small diameter.

it strange bc I don't see much OMC manufactoring the 14,25 except for the Viper that came w/ the ETEC. the rest of 14.25 are a few aluimins. I see 14.5 an 14.75 though.I'd like to try the right size in Stainless steel. thanks DogCavalry

 

[the brain]

my solas 19 (now relegated to a spare stowed) has much more fin surface than the Viper 22.
how does fin surface factor in?


my viper 22 fin has 4.5 inchs of surface area however there's much more cupping compared to the Solas. additionaly the viper appears to have some nicks image of both props.


the Solas has 5.75” I assume w/ more surface area there's more blade gripping water however less cupping.


I thought the solas was a bit beat an bent to even try for a shakedown.