When it comes to props I'm lost.....
 

My cig is running Bravo 1's with 1.50 ratio. I have 4 blade stainless 26p props on it. I also have a spare set of props that the previous owner said are more top end, but when I look at them I can only see a marking that say's 23p. They are 4 blade and look more like the cleavers I see on some of the boats. Owner says they were labbed too but trying to figure out how I determine that. I'll try to post a picture later tonight because I think I'm missing something. I though a higher pitch would be more top end. ???

Lower pitch will allow you to spin the engines to a higher RPM, thus more speed.

So, if my 502's are rated to top out at 5000rpm

A 26p at 5000rpm allows 70mph
A 23p at 5000rpms allows 73mph (not actuals, just for conversations sake)
?

I guess the confusing part to me is that my engine spec sheets say 5000rpm should be the top, and I can get that out of my 26p prop. If the 23p can spin the motor higher, that could potentially be bad? And they'd be the wrong prop anyway?

Slip is the real magic number. What engines do you have, 5000 rpm max??

Try them. A prop guy will tell you a Bravo 1 prop is -1 in pitch as far as they are concerned. So lets say your 26p is a 25p for true calculator. Your worked 23p with added cup, and labbed to reduce slip could out perform the 26p. But my guess is it will still also get you some more RPM.

I have carb'ed 502's (415hp). I have a spec sheet that came with them.. I could have misread and it was max HP at 5000. I just remembered a conversation with the seller and he mentioned that those props would be more top end than the 26p that are on there and when I saw a 23p marking, it just had me wondering. The 26's pull hard midrange, but was debating throwing the other ones on to try out.. I just am very novice in the prop world.

I can't believe you can pull those 26's up to 5k with 415hp. I had 560hp with the same prop spinning to 5200. Overall a bravo 4 blade is the right prop for a bullet.

Don't know what to tell you on that one lol... It will go higher with a lighter load.. Maybe a little less than half fuel and 3 people. On my GPS, I clocked it at 73mph... The boat likes to move. Maybe the drive ratio? I've got 1.5 Bravos.. Can't you get a 1.3 as well? Thats why I sparked the conversation.. My clueless prop knowledge haha

Efficiency remaining constant (same slip %), you would have to turn a 23 pitch prop 500 rpm faster than the 26 to run the same speed.
Therefore you would need to pull the 23 over 5500 rpm to gain speed over the 26.

Call us anytime and we can go into specifics for you.

Brett

i think so,Lower pitch will allow you to spin the engines to a higher RPM, thus more speed. thankshttp://goo.gl/XRZbT6

think of prop pitch as the gears on a 10-speed bike, you can go the same speed in lots of different gears all that changes is how fast you pedal. You will go the fastest in the highest gear. I lower pitch prop will equate to higher RPM but unless the boat was overpropped to start you won't go faster.

Correct.


Think of the 10 speeds of the bike a pitches. The engine has as much power as your legs. Your legs can pump 1st gear/pitch to the rev limiter (as fast as you can pedal).
But when you shift to 10th gear/pitch you can pedal only at a few revs per minute but the speed is the same. So, if you could pedal at rev limiter you would be going faster than the 1st gear on the limiter.

Going down in pitch and gaining speed will only be faster than the high pitch if the high pitch can't be turned fast enough to gain more speed. Point is, going down in pitch Does Not make you go faster all the time.

Does this make sense or am I being more confusing?

Brett

Also correct me if I'm wrong. As you move up in pitch say from a 23p to a 26p the boat theoretically moves forward further per each revolution of the 26 than the 23. So you have to spin the 23 higher to get more revolutions, since each rev isn't pushing the boat as far. If you cant overcome that in order to make up the difference the 23 won't be faster.

Me personally I would rather spin a 30p at 4800 and go 90 than say a 26p @ 5500 to do the sane speed.you'll have better cruise as well

Correct.

Of course the engines designed wide open throttle range is the determining factor for pitch choices.

Brett

[QUOTE=dsmawd350;4159354 Me personally I would rather spin a 30p at 4800 and go 90 than say a 26p @ 5500 to do the sane speed.you'll have better cruise as well[/QUOTE]


Correct?

In my opinion hardly correct, over prop it an you kill the bottom end, kill the mid range acceleration, kill the upper end acceleration, and end up going the same speed at some point when the slug manages to get there. If a few ounces of gas per hour at "cruise" is worth having a boat that overall performs like chit, over prop it and have at it.

I agree, not to mention it is propped to run all day at the peak torq, over propping is hard on the drive and engine as well. If she is made to run 5500, run her there. So many people are scared of higher rpm, I would rather let her sing a little unloaded than hold it back with too much load.

Interesting discussion.

Prop to the upper end of your recommended rpm range with a standard load in the summer (not on the limiter).
When it cools down or the load is light you may have to throttle back a touch.
Throttle response and acceleration and boat personality is a better overall and more usable equation. You will be a happier boater.

Then, build a prop for light loads, cool air, how fast does this SOB go situations.

One prop/set of props can't do it all.

Brett

I have an aceelerate like a MOFO prop.
I have a Top End Prop.
And I have a Prop that keeps the boat in the water and in control better for cruising with other people.

here is the simple rule I follow for finding the right pitch prop, it should be banging the rev limiter, when you are by yourself with no gear and stuff on the boat, and practically on fumes, and a cool day, with the wind behind you, ect ect.

If you do that you won't be lugging the motor on a hot summer day loaded with fuel, people, and stuff.

Also just because a higher pitch prop gets you a faster cruise speed at a given rpm don't assume you are saving fuel, typically the motor is working harder to do that and you are propbably getting worse mpg.

I will have to put a picture of the props up and see if any other markings are on them.. I just know the previous owner said I'd have more top end, but would lose some of the midrange.. With the 26's I have on there, it pulls hard under acceleration. The cruise is great

Maybe you should just try them and post the results? Spending all this time trying to figure what they are and what he had done to them over a forum is comical. Try them, you may like them better

I was more sparking the conversation to try and understand prop pitch a little more. At some point I will try them, but I started questioning when I noticed the markings on them and I was always under the impression, higher pitch, faster prop; lower pitch slower prop better for midrange.. You cant learn if you dont ask.....