Prop pitch?

[crotalis40741]

I apologise ahead of time for this dumb question. lol
If a motor calls for a 23 pitch prop would a 24 pitch prop cause problems? I don't know or understand
what the difference in pitch is for or does so if anyone could help me on that also it would be appreciated. Also how can you visually look at a prop and tell if it is a standard rotation or a counter rotation prop?
thank you
bob

 

[circle hook]

Re: Prop pitch?

i found that the pitch for any given engine will act different from one boat to another with different hull designs and weight changed in the boat extra fuel tanks etc. usually the lower pitch gives more power & less top end, where the higher pitch gives more speed, its up to what your looking for better fuel or more speed, but also you want to be in the operating range for your engine they vary but around 5,000 to 5,500 rpm at wide open thats ball park. hope this helps bob

 

[crotalis40741]

Re: Prop pitch?

i found that the pitch for any given engine will act different from one boat to another with different hull designs and weight changed in the boat extra fuel tanks etc. usually the lower pitch gives more power & less top end, where the higher pitch gives more speed, its up to what your looking for better fuel or more speed, but also you want to be in the operating range for your engine they vary but around 5,000 to 5,500 rpm at wide open thats ball park. hope this helps bob

Thank you very much, the reason I am asking is. I am looking at a 91' 18.5 foot basscat with a 91 Mariner 150 mag 2 and the owner discovered his original prop had a crack in it and he replaced the prop and then noticed the boat didnt want to go on plane. The original prop was a 23 pitch and the new one is a stainless 4 blade ballistic prop 24 pitch. The compression checked out at 125, 125, 125, 125, 118, 118 on the motor. I didn't know if the difference in prop size would cause the problem or it maybe he got the wrong rotation prop for the boat. I am having the carbs redbuilt and fuel lines were replaced. The motor doesn't seem to miss just bogs when trying to put it under a load to reach plane. The boat sat for a year and ran great before it sat.

 

[circle hook]

Re: Prop pitch?

think about it if it were the wrong rotation the boat would not go foward when shifted in foward, so thats not the problem and usually you can drop a pitch size when going from a 3 blade to a 4 blade. when trying to get up on plane try squessing the primer ball is sounds like you have other problems, like the fuel pump try the ball first if it speeds up then when pumping then you need a fuel pump try that first. compression readings look good. was any carb work done if so usually opening the needles 1/4 turn will help too. sounds like a fuel issue. or timming.

 

[crotalis40741]

Re: Prop pitch?

think about it if it were the wrong rotation the boat would not go foward when shifted in foward, so thats not the problem and usually you can drop a pitch size when going from a 3 blade to a 4 blade. when trying to get up on plane try squessing the primer ball is sounds like you have other problems, like the fuel pump try the ball first if it speeds up then when pumping then you need a fuel pump try that first. compression readings look good. was any carb work done if so usually opening the needles 1/4 turn will help too. sounds like a fuel issue. or timming.

Thank you for the reply. No carb work has been done since it has been sitting. I will try squeezing the bulb when I go look at it in the morning. He said he had replaced the fuel pump a couple years ago but being sitting it could have went bad or gummed. Am trying to get some basic ideas before I buy it and it turn out to be something really bad. I don't really know anything about the mechanics of the outboards. And really do appreciate the help. I do plan on having the carbs redone first thing if I do buy it. I figured it couldn't hurt since it has been sitting.

 

[oldman570]

Re: Prop pitch?

There is a good chance the carbs will need to be cleaned or rebuilt again if the motor has sit for sometime without haveing been preped for storage. Gas left in the carbs has evporated and the varnish has probbly pluged some of the jets and passages in the carbs. As for the prop you can go to
http://www.solas.com/newweb/propeller/tech/basic.asp and you can get a better understanding of what a prop should do for your setup. JMO
Oldman570

 

[steelespike]

Re: Prop pitch?

Very simply selecting a prop is like picking a single gear in a car to do everything.
Higher number pitch is more like high gear in a car.
The higher the pitch the harder to push the boat but if it can reach the rated rpm it may be faster than a lower pitch.
Lower pitch gives more power revs easier and has faster hole shot.Too low pitch and the motor may over rev.
The idea is to pick a prop that is a good compromise for power and speed and the motor can operate within it's wot rpm range.
The change to a 4 blade ss prop has a few things going against it to make a good match.The ss is more efficient and may load the motor more, a four blade adds resistance trying to reach rpm.Usually going to a 4 blade you would reduce pitch about 1 inch.
So the 24" is actually at least 2" too big.

 

[jestor68]

Re: Prop pitch?

If the boat doesn't want to plane off due to wrong prop/motor problem(s), you should consider not buying it until the seller gets it sorted out.

It's not your problem, unless you've already bought it(which would be a mistake).

 

[dan02gt]

Re: Prop pitch?

A 23P 3 blade would be what you want on that boat. The 24P 4 blade is too much prop. It's like starting off in 3rd on a car. Loose the ballistic and if nothing else pick up a used Laser II in 23P. They're plentifull on Ebay. If you want the best performance go with the Tempest Plus in 23P as it will give you better bow lift and carry a load better, but expect to pay a little more.

 

[dan02gt]

Re: Prop pitch?

If the boat doesn't want to plane off due to wrong prop/motor problem(s), you should consider not buying it until the seller gets it sorted out.

It's not your problem, unless you've already bought it(which would be a mistake).

Agreed 100% the seller should be fixing it. The original prop could also be fixed in most cases.

 

[crotalis40741]

Re: Prop pitch?

Thank you all for the help, I really appreciate it. I will have the seller change the prop and go from there.

 

[Chris1956]

Re: Prop pitch?

A 23" pitch prop is a bit unusual on that motor. Depending on the size of the boat, it is likely too much pitch. To use that prop would require that the boat be a high performance hull (like a bass boat) in the 16' range.

What you really want is prop that allows the motor to reach about 5500RPM, with an average load.

 

[jestor68]

Re: Prop pitch?

When all else fails, consult the Mercury prop selector. :joyous:

An 18 ft Basscat/150 Merc weighs 1750 lbs. Add 500 lbs for people and gear, and 25 gal of gas and the selector calculates the weight at 2392 lbs.

It comes up with a Laser II and/or Tempest Plus at 21 (or 22) pitch for good all around performance.

I used the Merc XR-6 in place of the Mariner Mag II.

The WOT rpm range is 5000-5600 rpm.

 

[dan02gt]

Re: Prop pitch?

A STRONG 150 can turn a 23P SS prop on a 18-19 bass boat very easily and get you into the low 60s. That being said if it's water logged or the motor is not in tip top shape or the boats carrying a lot of weight a 21P may be required.

 

[jestor68]

Re: Prop pitch?

A STRONG 150 can turn a 23P SS prop on a 18-19 bass boat very easily and get you into the low 60s. That being said if it's water logged or the motor is not in tip top shape or the boats carrying a lot of weight a 21P may be required.

And provide a very poor hole shot. A 23 is for that guy that only cares about getting that last 1 mph out of it. He doesn't care that it takes a long time to get on plane. :faint2:

 

[crotalis40741]

Re: Prop pitch?

I know some on here said it was a mistake to buy the boat but I got it this morning, the seller gave me money off because of the prop issue. Had the motor checked out and it checked out ok. Still has good compression but could use a carb rebuild. Which is about to be done along with rebuilding the fuel pump. I am selling the 24 pitch prop and getting a 21. I just want all around good performance and something that doesn't over stress the motor. I really do appreciate all the input and help. So now to post a prop on CL lol

 

[dan02gt]

Re: Prop pitch?

And provide a very poor hole shot. A 23 is for that guy that only cares about getting that last 1 mph out of it. He doesn't care that it takes a long time to get on plane. :faint2:

I think you'll find that almost every modern 18' bass boat with a 150 runs something in the 23P range. A strong 150 like a Optimax pro xs or ETEC is going to live on the rev limiter with a 21P prop on any performance bass boat hull. Heck I run a 21P on my 18' fish and ski that's 270lbs heavier than a comparable bass boat and my Opti can turn it to 5700RPMs at 57.x MPH GPS with 3 people and 30 gallons of fuel. And my hole shots great even with it loaded to capacity.

 

[jestor68]

Re: Prop pitch?

I think you'll find that almost every modern 18' bass boat with a 150 runs something in the 23P range..

That's like saying all brands of 18 ft bass boats are created equal and all will run the same pitch props.

 

[dan02gt]

Re: Prop pitch?

That's like saying all brands of 18 ft bass boats are created equal and all will run the same pitch props.

For the most they are about equal with the exception of the hand build ultra performance bass boats like a Stroker, Allison, or Bullet. In general most 150 powered 18' "cookie cutter" glass bass boats run in the low 60s with proper setup and use props in the 23P range to get there. If they're running something like a Yamaha they may run a little more pitch because of it's gear ratio. Honestly, I don't know crap about 95% of the boats people post about on this forum but I know bass boats. Take a look a the bass boat setups on Bass Boat Central and tell me how many guys are running 21P props on 18' 150 powered boats. I bet not 1 in 10, and the other 9 don't have crappy hole shots. Where talking 1400lbs padded-v hull boats that carry 2 people here not 2500lbs bow riders carrying 6-8 people. Will a 23P work on every 18' 150 powered bass boat that still floats? Not sure on that but in general it's what you want.

 

[dan02gt]

Re: Prop pitch?

crotalis40741 here is a list of Bass Cat setups. I don't know what your particular model is but this should give you something to go on.

Basscat

As long as the boat and motor is in good shape I wouldn't worry to much about the prop thing. Find a shop that will let you test a few and buy the one that works the best. I would recommend testing a Mercury Tempest Plus.