need help figuring out correct prop

[Terryfish]

I bought a used 20" cobra viper bass boat and the prop blades had been shaved off, when I contacted dealers about the correct prop for the motor ..no one seemed very interested in helping me select the right prop so I read various forums trying to get an idea what would work for my setup and searched online for a good deal and the customer service at a marine supply told me the prop i was looking into was the right prop for my boat..well i got it and right away the hole shot was much better but not too much after that..felt like 4800 rpm's was about all I was going to get out of it but I can get it to 5200, also VERY torquey...the old prop is a 13 1/4" omc shooter prop....the new prop is a Solas 14" ...both are 4 blade props...so my question is, what is a good prop for my 97' 20' cobra bass boat with a johnson 200 venom? How can I get the right prop that will allow me to a decent hole shot and speed without tearing up my motor...the motor runs really well for a 96' idling or full throttle, with the old prop she sings really happy and smooth but only 52 mph with a good wind at my back.....any suggestions, advice or help of any kind would be greatly appreciated!

 

[jimmbo]

Since you don't mention what pitch the props are, it is going to take more info to fix/improve your issues. When you say "Shaved Off", do you mean someone cut them down, or they are worn down from running is sand? You are able to get it up to 5200 rpm. If the tach is accurate, that is in the lower half of the WOT rpm range, which is 5000 - 6000.
Is the motor in good mechanical shape? Good compression, fuel system good, Ignition system timed properly? What condition is the boat in? Any Hooks or Rockers? Any trapped water in hollow compartments, water soaked floatation foam? If the engine, boat, and tach check out, then you are over propped. you are about 800 rpm short of your goal, which would mean dropping 4 inches of pitch.
Of course we don't know the setup(engine height, trim angles, set back if engine is on a jack plate. Those items will affect top speed and rpm too

 

[Watermann]

A better hole shot normally doesn't coincide with fewer RPMs at WOT, it should be just the opposite as pitch is what controls that not the diameter.

"Happy and smooth" with the old prop means replace with the same diameter and pitch new prop.

 

[211libwtfo]

I’ve got a ballistic prop and it looks like the tips have been shaved but it’s by design.

 

[Terryfish]

Sorry I didn't mention the old and new props are both 25 pitch, the engine is sound..good compression, relaced stator , regulator/rectifier and timer base after I bought it..the motor is running really well..when I said shaved off I meant the ends of the blades were actually missing about a quarter of an inch or more ,they had been evenly cut or grinded off possibly, the diameter measured 12 1/2" and the measurement on the prop says 13 1/4", the engine is on a jack plate and the middle of the prop is right about 3" below the pad best I can measure,the boat is dry in all compartments and hardly takes on water if any, I did some checking and the old prop shows it is for an 89' johnson 200...mine is a 96'...cant find any info at all on the boat..viper boats have been out of business for some time

 

[jimmbo]

When you replaced the timer base, did you check the max advance for the timing?

This is kind of confusing, "felt like 4800 rpm's was about all I was going to get out of it but I can get it to 5200,"

What are you using to get your MPH? Water speedo or GPS? That pitch at 5200rpm, allowing 12% slip, calculates faster than 52mph

 

[Terryfish]

Let me rephrase that, when I get up to about 4800 rpms the motor feels like its maxed out already but I can get it to hit 5200 on a straight run ..that's what I mean when I say I don't want to tear up my motor, I'll get back to you on the timer base..had someone install that for me...I really appreciate your response, apologize if I sound confusing, I'm fairly new to boat motors

 

[Watermann]

If the ends of the blades have been removed then that means the cupping is gone as well, which will also cause an increase in RPMs for that prop. I would go down to a 23p prop if it were me.

To be sure you are trimming the motor out appropriately once your up on a plane and running?

 

[jimmbo]

Cupping adds Pitch and/or Rake. If the cup is on the trailing edge of the blade it adds pitch, cupping on the tips of the blades adds rake.A reduction of trailing edge cupping should increase RPM, and a loss of tip cup would reduce the props bow lift ability

 

[Terryfish]

Yes I am trimming up the motor once I get on plane..so you would you stick with the 13 1/4 prop with lower pitch? I don't think I mentioned I was able to find out the old prop is an omc shooter prop meant for an 89' johnson 200..mine is a 96'...thanks for all the info/help!

 

[jimmbo]

The shooter can be used on any engine that it fits, year or horsepower doesn’t matter. Whether or not it will be the best prop for that application is another matter.
You seem to have fixation regarding the 13 1/4 in diameter. Different prop lines/models/brands will have different diameters. Let the prop engineers worry about diameter.
If you motor is in proper tune, has good compression, is mounted at the prop height for the type of prop you are running, and the tach is accurate, then yes you do need a lower pitch prop. Myself I would get rid of the 4 blade, get a RAKER or Enertia which are 3 blades and drop to a 22 in pitch.

 

[Terryfish]

Ok, thanks for the info and advice..I will look into those props...just curious..have you heard of having a prop repitched? Is that a wise thing to do to the new 14" prop or just get a new prop?

 

[jimmbo]

Repitvhing a prop is not something I would ever recommend. It involves bending/twisting the blades from the shape they were cast. The odds of getting all the blades bent/twisted identically, is a long shot. I have never seen a repitched prop perform anywhere near as well as a non adjusted prop of the proper pitch.
Others may have a differing opinion

 

[Terryfish]

yeah, I'm thinking about the props you mentioned

 

[Faztbullet]

Either the boat is water logged or the motor has a problem as that rig should turn the crap out of a shooter 25P. You don't need to drop below a 24P if hull/motor/set-up is correct.

http://www.bassboatcentral.com/viper.htm

 

[Sea Rider]

1 inch repitch is usually done when there's no intermediate size between two full sizes, say a 14 and a 16 pitch prop or a 0.5 inch repitch between one full pitch say 13-14 pitch props. It's a fine tuning thing if like running full wot revs as loaded and 2 full or one full pitch props still dials too much wot rpm.

Reputed old prop shops with correct prop tooling along skill should honor their work with no problem..

Happy Boating

 

[Terryfish]

The boat is not water logged, all areas are dry..no standing water and I'm assuming the flotation material is ok because the boat hardly picks up any water at all after a full day on the lake,the motor is strong..it turns 6000 rpms( I dont do that but it can) with the old 25 pitch shooter prop, around 5800 it runs really smooth but I;m only pushing 50 mph...with the new 14x25p prop it launches the boat out of the water and up on a plane very quickly but tops out at 5200 rpms and I get about the same top speed around 52 mph, very frustrating...what is the right combination...grrrrr..wish I could find the factory recommended prop for my setup

 

[Terryfish]

best way I can describe running with new 14x25p prop is like running in low gear with no overdrive

 

[211libwtfo]

Not to turn “business” away but on offshore only forums there’s a guy there ken, he IS the prop god.

 

[Terryfish]

wondering if I can go higher with the motor..last time I measured the middle of the prop was 3" below the pad