1.62 vs 1.75 Revisited

[Largemouthlou]

Jason, thanks again for letting me borrow the 1.75's for a few weeks :D

There is a big difference and at the moment, I'm still a little confused by the driving and handling differences.

Yesterday wasn't the best day to do this due to the swirling winds in the canals at Holiday and hard to learn the differences with the 2 partners I had (Neil out of balance and Deana being a speed limiter :mrgreen: )

It is different for sure compared to 1.62's I tried a 32 4 blade performer ET cut for fishing and it was different some times acting like it wasn't carrying the load and others seemed fine..

I tried my 28 Bravo in the afternoon and it had a hole shot like a Bat out of hell and excellent acceleration for sure, but like Jason said I have to get used to catch up with the off shore trim..

Even with Neil in the boat (290++) it had an excellent Hole shot and you can feel the acceleration better..

Is there a point on a prop that was worked for 1.62 gears that it can be twisted to fast with the 1.75's that there isn't enough cup for the prop to grab???

Sort of like the car push on the gas and it goes, stomp on the gas and it smokes the tiers..

[John Jackson]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by trashy &raquo;</TD></TR><TR><TD CLASS="quote">
My guess is yes, you're going to get more slip from a prop worked for 1.62's.

</TD></TR></TABLE>

The higher the pitch on a prop, the less cupping it can have before it goes into hydraulic lock at speed. And with the current diameter props, best efficiency is on props around 25" pitch. The more you deviate from that, the more loss of efficiency, (if everything else is constant/the same). But there are way too many variables from one prop to another, even the same make, model, and pitch prop.

[John Jackson]

It's kind of hard to explain on effeiciency, but racing has proved it out. If you could go to a 30" diameter prop, then pitch would need to increase to increase effeciency. The blade angle where the prop does the majority of it's work is most effecient at a particular angle,roughly 45*, where the rotational force is equally converted to foward directional force. As you approach 0* or aero pitch, you have no foward force, just wasted energy. As you approach 90*, or infinite pitch, you also have no foward force, just a paddle wheel that will turn a surfacing propped boat in cireles. In between pitches above the optimal lose efficiency to the paddle wheel effect and less mechanical leverage. Below optimal pitch and you lose effeciency to friction and less thrust.

As for cupping, try & picture in your head the trailing edge of the prop. If you are running props in the 30+ pitch range, the blade angle is already pretty severe. No roll the trailing edge several degrees for cupping. Go too far, and you may be at infinite pitch at the trailing edge or beyond.

For an exagerated example, lets say you add 30* cuping (I've seen more than this on some props), your 45* blade angle is now 75* at the trailing edge. Now take a 36 pitch prop of the same diameter, with a blade angle of 65*, now add that same 30* cupping to the trailing edge and you have a pitch that is like a LH rotating prop. It's trying to drive the propulsion force in the opposite direction.

[Largemouthlou]

I was turning a 28 bravo to 6900 @ 93 mph and with the amount of beef (550#) and full fishing load, 10 - 15 gal gas, that worked out to 11% slip +/- (1.75 gears)

I can turn the same prop on 1.62 gears to 6550 at usually 95 to 97, I would think with the load it would have ran the same speed of 93.. (1.62 gears)

Also seems that I can go down to a worked 26 Bravo with 1.62's and get the same results as running a 28 Bravo with 1.75 (better then usual hole shot and higher rpm's if needed..

So where in this mess does turning a bigger pitched prop more rpm's equal more speed?? I have turned the 4 blade ET cut to 10X at 6200 which is right at the WOT range of my motor. So with the 1.75 gears and same prop will I just be turning more R's and doing the same speed?????? That is what it seems like.

Does seem like the 1.75 may be good for a summer lower unit

Just trying to figure this out, and will be running them again next weekend so I have to learn the motor trim combo all over again with the 1.75s

[John Jackson]

Divide the motor RPMs by the lower unit ratio to get the prop RPMs.

[Largemouthlou]

That is the same thing Conner was explaining to me..

the 1.75 actually turn less revolutions with the same prop at higher rpm's then the I.62 gears do at lower rpm's

[John Jackson]

A good way to explain it is using your 6900 RPM, with 1.75 gears the prop is turning 3943 RPM, and with 1.62 gears the prop is turning 4259 RPMs at the same 6900 motor RPMs. .

[Largemouthlou]

Yes, those were the #ers I ran last night.. This has brought a lot to light that I have never considered, Thanks John, Connor and gang for all this info..

Not sure what I will do with it but it is very interesting learn for sure..

[spider1]

Lou you take this info and bolt a prop on and run it to see if you like it or not!!

[Largemouthlou]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by spider1 &raquo;</TD></TR><TR><TD CLASS="quote">Lou you take this info and bolt a prop on and run it to see if you like it or not!! </TD></TR></TABLE>

Now look at what ya made me do!!!!!!!!

Picture deleted by insurance company

[spider1]

Sorry! I really hate that I did that to ya!

[Meyers]

Alright Lou...now I have to ask??? Are you thinking that the 1.75's are a better fit due to the fact that the prop is not working (turning as many rpm's) as hard?

The 1.75's would probably always provide a little better holeshot but dosen't that mean a larger pitch prop for running?

I have been passed on take off during a tournament due to the 1.62 gears but I usually go right past them once on plane???

[1outlaw]

On Lou's set-up i believe the trim will be the only thing that would hold him back from a acceleration standpoint from a dead stop!!!..........I know that with the 1.75 i will out accelerate Lou, Connor, Dan, And Blair (Blackie)....When Blair runs Nightmare we stay side by side until we reach the 80's and he starts walking by...Obviosly the extra H.P. and lighter boat make up the difference of the gears!!!!

[spider1]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Meyers &raquo;</TD></TR><TR><TD CLASS="quote">
I have been passed on take off during a tournament due to the 1.62 gears but I usually go right past them once on plane???</TD></TR></TABLE>

It is not the 1.62 gears that is the reason you are getting passed. If you drop your prop down by 2 pitches say from a 30 to a 28 or a 28 to a 26 and then see how it will stand to the other boats that are passing you.

[Largemouthlou]

Bryan, for the little time I have had to play with the 1.75's I don't want to answer that yet.. I have run all the # in my mind and on the prop slip calc and come to the conclusion that,,,,,,,,,,,,,,, I'm not sure!!

Conner is correct that if I have a 26 worked for the set up of 300X 1.62's I think it will compare to the 1.75 acceleration and hole shot and would have to think 95+ with a fishing load is due able but will be close to the limiter..

I personally like to run my motor to about 6500 to 6700 that is well into the power band of the 300X as the book says that WOT starts at 6200 and the limiter is at 7000 on mine

Jason, I do think some of the mods to your motor help with the hole shot and mid range also..

So I have come to the conclusion that I have no conclusion at this time

[spider1]

Lou it also depends on what you are looking for and what motor you have.
Like mine has a limiter of only 6150 so a small prop will not give me the speed and with the 1.75 I have to run such a large prop to stay out of the limiter that there is very little difference between the two gears.

Jason you also have to think about set up as set back and weight. Lou's and my boat weights about 100lb more then your. That is for the driver and ballist! and we are running a lot more set back about 4 inches which hurts hole shot also.

[1outlaw]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Largemouthlou &raquo;</TD></TR><TR><TD CLASS="quote">Jason, I do think some of the mods to your motor help with the hole shot and mid range also.. </TD></TR></TABLE>

What mods???....I have no idea what your talking about!!!!

Connor go on a diet if your Concerned the little old 225 is gonna be out front

[spider1]

Hell Jason that little 225 has been in front from day one!!!! And I am not going to stop eating!!!

I always thought that you motor was stock!

Hope I can make it Sat. Always a blast when the bunch of us get together!!!!

[Largemouthlou]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by spider1 &raquo;</TD></TR><TR><TD CLASS="quote">

Jason you also have to think about set up as set back and weight. Lou's and my boat weights about 100lb more then your. That is for the driver and ballist! and we are running a lot more set back about 4 inches which hurts hole shot also.</TD></TR></TABLE>

Um that is incorrect !!!!!!!!!!! Jason is 100#wet, I'm 230# that is a 130# more so ya double that to balance the boat and it equals 260# of extra weight in the boat!!! Now should we talk about boat weight

[spider1]

Lou sounds like you are the one that needs to talk about a diet!