Best prop for my 1985 Blackmax 150

[tysdad2010]

Currently I am running a stainless steel 25 pitch 3 blade prop...it does fine...but i am looking to gain some speed and maybe better hole shot also... what would you recommend? The boat is a 1986 V371 Ranger 18ft I beleive...I just looked at my reciept from the boat shop when i had my lower unit replaced they wrote on the receipt 23p SS but put a 25p

 

[Barnacle_Bill]

Re: Best prop for my 1985 Blackmax 150

How many RPMs are you turning at WOT?

 

[tysdad2010]

Re: Best prop for my 1985 Blackmax 150

How many RPMs are you turning at WOT?

What does WOT mean?

Well I dont have a Rev limiter on this motor b/c it had frayed wires on it so i took it off and looked up how much it was to replace it so I said hell with it...I try not to turn over 5500RPM's but I can turn up to like 5700-5800 max

 

[1nebel0]

Re: Best prop for my 1985 Blackmax 150

You could possibly turn a 26 but will lose some hole shot...there is nothing wrong with your rpms...good gas, good oil and correct timing and you will not harm the motor.. I have a couple of 200 fishing motors and spin them 6000 all day long...you don't say if those rpm's are loaded or unloaded as that will make a big difference...remember lugging a motor is far worse than taking the rpm's past the book rec's..

 

[tysdad2010]

Re: Best prop for my 1985 Blackmax 150

You could possibly turn a 26 but will lose some hole shot...there is nothing wrong with your rpms...good gas, good oil and correct timing and you will not harm the motor.. I have a couple of 200 fishing motors and spin them 6000 all day long...you don't say if those rpm's are loaded or unloaded as that will make a big difference...remember lugging a motor is far worse than taking the rpm's past the book rec's..

So the higher the pitch the more faster my boat will go? Also what do you mean by my rpm's being loaded or unloaded? and what do you mean by lugging the motor also... i am not up to all these tech terms sorry...

 

[tysdad2010]

Re: Best prop for my 1985 Blackmax 150

You could possibly turn a 26 but will lose some hole shot...there is nothing wrong with your rpms...good gas, good oil and correct timing and you will not harm the motor.. I have a couple of 200 fishing motors and spin them 6000 all day long...you don't say if those rpm's are loaded or unloaded as that will make a big difference...remember lugging a motor is far worse than taking the rpm's past the book rec's..

So the higher the pitch the more faster my boat will go? Also what do you mean by my rpm's being loaded or unloaded? and what do you mean by lugging the motor also... i am not up to all these tech terms sorry...

 

[tysdad2010]

Re: Best prop for my 1985 Blackmax 150

please help...I would like to gain some more speed and hole shot...thanks...

 

[Barnacle_Bill]

Re: Best prop for my 1985 Blackmax 150

WOT is wide open throttle. Your motor should run between 5,000 and 5,500 RPM at WOT. Anything below or above that and you are loosing power. http://www.boatfix.com/how/props.html

 

[skibrain]

Re: Best prop for my 1985 Blackmax 150

I'll jump in here.

The pitch number on the prop is the distance the prop would move forward in one rotation (if there were no slip). So a 25" pitch is like a higher gear in a car. For a single rotation it will move you ahead 25". For a single rotation a 21" pitch would move you ahead just 21"

I have said nothing yet about speed.

The reason that people have asked about WOT is to determine how fast your motor on your boat is able to spin the prop. If you were over-loaded or did not have enough horsepower for the weight of your boat, etc. your max rpm would be lower, like 4500 to 5000 rpm indicate that your motor is struggling against the load. Make sense? People might call that "over-propped" like trying to drive a manual transmission car up a hill in 5th gear and you can't get the rpm up....if you shifted down to 4th or even 3rd in the car so the engine rpm is higher, you might go up the hill FASTER.

Since a boat only has one "gear" or prop pitch to work with, it is always a balance of which prop that will give you good acceleration and best top speed. If you dropped way down, to say a 19" pitch, your hole shot acceleration would be tremendous but you might loose 5-7 mph on top end.

So back to your boat. The general rule is that you want a engine/prop set up that will allow you to achieve your max-rated rpm at WOT. If you are revving too high (say 6000 rpm) that would indicate too small a pitch, and you maybe COULD see an increase in speed with a higher pitch. Someone else here will know the rpm sweet spot on the Black Max 150, but 5700 range sounds to me like you're set up pretty well. Getting BOTH more speed AND hole shot is unlikely with your current boat.

- If you could make your boat LIGHTER there could be less drag and your boat might be able to turn a bigger pitch prop fast and make you go faster.
- If you put a transom jack on your boat and were able to lift the motor out of the water at speed to reduce drag of the lower unit in the water, you may also be able to turn a bigger prop fast and go faster.
- Or you could put on a 200 hp motor.

Prop experts: how did I do?

 

[tysdad2010]

Re: Best prop for my 1985 Blackmax 150

I'll jump in here.

The pitch number on the prop is the distance the prop would move forward in one rotation (if there were no slip). So a 25" pitch is like a higher gear in a car. For a single rotation it will move you ahead 25". For a single rotation a 21" pitch would move you ahead just 21"

I have said nothing yet about speed.

The reason that people have asked about WOT is to determine how fast your motor on your boat is able to spin the prop. If you were over-loaded or did not have enough horsepower for the weight of your boat, etc. your max rpm would be lower, like 4500 to 5000 rpm indicate that your motor is struggling against the load. Make sense? People might call that "over-propped" like trying to drive a manual transmission car up a hill in 5th gear and you can't get the rpm up....if you shifted down to 4th or even 3rd in the car so the engine rpm is higher, you might go up the hill FASTER.

Since a boat only has one "gear" or prop pitch to work with, it is always a balance of which prop that will give you good acceleration and best top speed. If you dropped way down, to say a 19" pitch, your hole shot acceleration would be tremendous but you might loose 5-7 mph on top end.

So back to your boat. The general rule is that you want a engine/prop set up that will allow you to achieve your max-rated rpm at WOT. If you are revving too high (say 6000 rpm) that would indicate too small a pitch, and you maybe COULD see an increase in speed with a higher pitch. Someone else here will know the rpm sweet spot on the Black Max 150, but 5700 range sounds to me like you're set up pretty well. Getting BOTH more speed AND hole shot is unlikely with your current boat.

- If you could make your boat LIGHTER there could be less drag and your boat might be able to turn a bigger pitch prop fast and make you go faster.
- If you put a transom jack on your boat and were able to lift the motor out of the water at speed to reduce drag of the lower unit in the water, you may also be able to turn a bigger prop fast and go faster.
- Or you could put on a 200 hp motor.

Prop experts: how did I do?

Thanks So much for taking your time to explain what I needed to know! That helped alot for me to understand...But what does it mean but lugging the motor? What do ya'll think about trying out a 24p stainless prop? I found one local I can pick up for $50 used in GREAT shape...should I be able to tell any difference if any?

 

[skibrain]

Re: Best prop for my 1985 Blackmax 150

$50 is an inexpensive experiment. My prediction is that it will have slightly better acceleration, rev a bit higher on the top end and at 6000 rpm be about the same mph as your 25" pitch at 5700 rpm.

Lugging. If you put for example, a 28" pitch on your boat my bet is your motor would not have enough power to spin it into your max rpm range when wide open. If your WOT only gave you 4500 rpm, it would be lugging the engine with too much pitch (think too high a gear in a car) What you're doing trying a different prop is the best way to find out.

 

[Number 1]

i have a 1986 skeeter startfire ss 175 black max always 2 people on boat was wondering whats a good prop size it dose 5800 6000 rpm quick no problem i have a 25 pitch prop max speed is about 52 mph seems slow to me but never gps it yet but boat plans out quick but i fill like maybe the prop is to big i see people talking about the 23 pitch is better but trying to make sure before i buy a new prop i cant find what size prop they came stock for this year thanks

 

[GA_Boater]

i have a 1986 skeeter startfire ss 175 black max always 2 people on boat was wondering whats a good prop size it dose 5800 6000 rpm quick no problem i have a 25 pitch prop max speed is about 52 mph seems slow to me but never gps it yet but boat plans out quick but i fill like maybe the prop is to big i see people talking about the 23 pitch is better but trying to make sure before i buy a new prop i cant find what size prop they came stock for this year thanks

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