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areamike

Prop questions holeshot versus top-end

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areamike

I have read through a few other posts here and this is one I found

http://www.themalibucrew.com/forums/index....merhead+sticker

Although the topic starter in that post wants more hole shot. I on the other hand want my WOT RPM to come down.

Right now I run a 13x13 SS 3 blade. at WOT the boat runs 49-49.5 @ 5600 rpm. The 5600RPM is what scares me. I don't like it.

I'm not too worried about losing any hole shot considering the boat will about pull your arms off your body already. What I want is to bring that WOT rpm down to a more "comfortable" number.

Any recommendations?

Also, what is the rev-limiter set at on these HH motors? I have the 365, and the motor was rebuilt and bored 30 over. Replaced all the cheap cast pistons and rods with forged ones.

Edited by areamike

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NorCaliBu

So go to a steeper pitch. I have a 13 X 14 OJ Legend 4 Blade as my back-up prop for my sporty (it was the OE prop but has since been replaced) and with just a 310 carbie it'll run 53.2 mph @ 4950 rpm. Contact Max at Skier-To-Skier he was a great help in my selecting the OJ XMP 13 X 12 CNC'd 3 Blade to replace the Legend.

Edited by NorCaliBu

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areamike
So go to a steeper pitch. I have a 13 X 14 OJ Legend 4 Blade as my back-up prop for my sporty and with just a 310 carbie it'll run 53.2 mph @ 4950 rpm. Contact Max at Skier-To-Skier he was a great help in my selecting the OJ XMP 13 X 12 CNC'd 3 Blade to replace the Legend.

So is 13x12 a higher pitch?

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NorCaliBu
So go to a steeper pitch. I have a 13 X 14 OJ Legend 4 Blade as my back-up prop for my sporty and with just a 310 carbie it'll run 53.2 mph @ 4950 rpm. Contact Max at Skier-To-Skier he was a great help in my selecting the OJ XMP 13 X 12 CNC'd 3 Blade to replace the Legend.
So is 13x12 a higher pitch?

No. I reduced pitch to get a little better holeshot and better speed holding characterists.

The first number is the diameter and the second number is the pitch. The higher the pitch number the steeper the pitch.

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hotrodbowtie

The general rule on a ski boat is for every pitch up you go, you will decrease 200-300rpm. If you decrease pitch rpm's will increase. A 3 blade prop is typically a better speed prop (skiing/barefooting) IMHO, so I would stick with a 3 blade ss with the same cup that you currently have and increase pitch to a 13x14. Also, You might not have a rev limiter and if the motor was built healthier, you do probably want to drop rpm's to around 5200. You might want to have your tach verified before you go to a new prop as a first step. Also, you can probably talk to your dealer or a prop shop and get them to sell you one with the understanding that if it does not do all that you need, you can change to a different prop.

Good luck

Thumbup.gifThumbup.gifThumbup.gif

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wienrdog

Also, the newer CNC & Cupped props from Acme/OJ have different RPM characteristics than their older counterparts. I went from an OJ Legend 4 Blade 13x13 to a OJ XMP 3 Blade 13x11.5 .09 Cup and maintained about the same RPM/Speed characteristics. I needed a back-up & wanted to improve the slalom performance a little.

As others have said, contact the guys at either OJ or Acme or Max @ Skier to skier. From the sounds of it, you'll likely want a 13x13 to 13x14 3 Blade CNC prop to drop WOT by about 400 RPM.

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areamike

Thanks guys great advice. Exaclty what I wanted to hear.dropping the WOT rpm about 400 would be perfect.

I know a guy over at the marina here...possibly he has a 13x14 I can "try before I buy" sort of deal.

I've also email Max at skier to skier to see what his opinion is.

Hey hotrodbowtie, How can I verify my tach?

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wienrdog

Talk to the guys at Acme & OJ. They will typically allow you to try & return if you're not happy. I know several others on this forum did that during the group buy last spring. They went back & forth between the 13x11.5 & 13x12 and in one case worked with the manufacturer to create a custom prop pitch/cup combination now available as a special order.

They may have a 13x14 there, but it will be a big difference between CNC/non-CNC & 3/4 blade props of the same size for WOT numbers.

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areamike
Talk to the guys at Acme & OJ. They will typically allow you to try & return if you're not happy. I know several others on this forum did that during the group buy last spring. They went back & forth between the 13x11.5 & 13x12 and in one case worked with the manufacturer to create a custom prop pitch/cup combination now available as a special order.

They may have a 13x14 there, but it will be a big difference between CNC/non-CNC & 3/4 blade props of the same size for WOT numbers.

why does it have to be so confusing.... Dontknow.gif

ugh. Thanks for the tip

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D-GOOSE
Talk to the guys at Acme & OJ. They will typically allow you to try & return if you're not happy. I know several others on this forum did that during the group buy last spring. They went back & forth between the 13x11.5 & 13x12 and in one case worked with the manufacturer to create a custom prop pitch/cup combination now available as a special order.

They may have a 13x14 there, but it will be a big difference between CNC/non-CNC & 3/4 blade props of the same size for WOT numbers.

why does it have to be so confusing.... Dontknow.gif

ugh. Thanks for the tip

this is just the tip of the info you could be receiving. Thumbup.gif

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areamike

Here's what Max at SkiertoSkier had to say

With 365 horses, I would suggest we start with the 3 blade XMP with a 12 or

12.5 pitch. That should get us close. OJ will do a prop tweak for free if

you want to fine tune.

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NorCaliBu
Here's what Max at SkiertoSkier had to say
With 365 horses, I would suggest we start with the 3 blade XMP with a 12 or

12.5 pitch. That should get us close. OJ will do a prop tweak for free if

you want to fine tune.

With your extra HP I'd go with the 12.5 pitch (or maybe even a 13 pitch). My 310 spins the 13X12 no problem. Oh to have 55 more more HP Drool.gif.

The XMP's are awesome props. If you don't have a puller...get the complete kit...it's like $400 for the prop, kit, case,...everything (including shipping). Thumbup.gif Or at least it was about a year ago.

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areamike

I already have a 13 pitch SS. Is the OJ 13 pitch going to be different?

I also have a prop puller.

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NorCaliBu
I already have a 13 pitch SS. Is the OJ 13 pitch going to be different?

13 pitch is 13 pitch...the difference comes in the size of the blades. The XMP being CNC'd will have much larger blades. Larger blade = more "push" on the water. You could also look at an increased "cup" on the blades...that's what made the Edwin Special special.

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D-GOOSE

The CNC will also have more flex then the SS. From what I have read and know the OJ 352 13X12.5 3 blade .110 cup would be a great start and not sure if you would have to make any changes but with OJ you will have that option.

Go with the 110 cup to help top end and lowering the RPMS.

Seeing how people keep talking about the Edwin special I figured I would pull up one of his old reports.

I'll put together a full report when I get a few mins. In short, Give Eric a ring and see what he has to say. FWIW, my ACME 13x12 stocker and OJ 13x12 run virtually identical rpms across the entire range. PP baselines are within a few rpms, WOT is within a 25 rpms of each other, etc. Top end speed is within .2 mph as well.

My edwin special is a 13x11.5 XMP with .120 cup. The goal was to create the holeshot of the ACME 13x12 with the skiing characteristics of the OJ 13x12. The standard 13x11.5 would spin more rpms than the 13x12 I already have...not what I was looking to do. By adding all the cup, it slowed down the rpms a bit. In short, I have what I believe is the best of both worlds for my use. I get a strong holeshot, 3350 rpms at 34mph, and the great wakes of the XMP. My top speed is down about 1.5 mph from the other props but I realized that was going to happen when I added all the cup to the 13x11.5.

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areamike

Hey I just got another reply from Max. tell me what you think.

Sounds like he knows what he is talking about. But hey, so does the Crew! Rockon.gif

Obviously, there really is not way to "know" which prop will be the exact

match for the motor as it is not stock. My experience is that it is much

better to have a prop that is too small than too big. None of us run our

boat at wide open throttle other than for a little foot'in -- and those are

short runs in which the driver needs to pay a lot of attention to tach and

speed. In slalom at 34 mph, it is much better to have the extra rpm to

match the peak hp/torque if you are pulling big guys into shortline.

Otherwise the boat is catching up with the skier when he is at the ball --

which is terrible for the skier. If you are pulling a skier at 34 mph in

the course, a tach of 3480 is often normal. Mine is 3520 but I am pulling

guys into 41 off at times. I would really not want to see the tach at 34

mph below 3400 as you are moving the wrong direction from the hp/torque

curve.

I would say to start with the 13x12 XMP 3 blade and give it a try. That

prop is a half pitch over what we would say to put on your boat for factory

stock engines. If you want to chop some more RPM, you can have it custom

cupped. The XMP 3 blade has a lot larger fin area than the standard 3

blade. Why 3 blade -- less leading edges to shear air out of the water at

the higher RPMs. Should be a better firmer pull. 4 blades shine on boats

with gear reduction or boats at slow prop rotation speeds (IE: wakeboard or

wake surfing).

Edited by areamike

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areamike

So, from what I understand. The OJ props can be re-cupped and modified slightly rather easily?

I'm guessing the OJ would be my best choice. As for starting Cup size, I'll need to figure that out. and 12.5 or 12...need to figure that out too...Too many options Dontknow.gif

LH or RH?

http://www.wakesiderides.com/rides/files/f...c--2347_468.jpg

Edited by areamike

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wienrdog

Since you said you want to drop 400 RPM or so and the OJ XMP 13x11.5 .09Cup is pretty much the equivalent of your current prop....

The difference is about 200 RPM for each inch of pitch changed. A 13x13.5 should get you that 400 rpm, but might be a little aggressive (below optimum torque range) at skiing & boarding speeds. It's also not a stock size for an OJ XMP Prop.

As Max said, going a little smaller the 13x12.5 .11 (OJ 340) should help with skiing RPM. That's the same size as recommend by D-Goose above, but for a keyed shaft instead of the splined shaft 352. You'll need to look at your boat to see if it's keyed or splined. Most Bu's are keyed.

OJ Prop list.

Edited by weinrdog

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areamike

I have keyed shaft. I think it is 1 1/8 and not sure LH or RH.

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areamike
LH

thanks VIN !

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hotrodbowtie

I will start with maybe I'm wrong but.....

For a 13 dia X 13 pitch: In a perfect world you have 13 inches of forward travel for every rotation of the prop, Thus the 13 pitch.

You can also affect things by changing your diameter. A larger diameter prop will throw more water and use more torque to turn. As the diameter gets larger the blade gets larger. traditionally a 1/4 inch diameter change is equivalent to 1 pitch.

Three blade vs four blade. Traditionally more blades equal more bite with the prop. (like traction in a car) More blades also creates more drag though. For wakeboarding consistent pull at slow speed is very important. For skiing and barefooting (high speeds) less drag enables the motor to run more efficiently. At high rpm's the motor has so much more torque that it provides the consistency that a four blade provides at lower rpm's. Racing applications can use as little as a 2 blade prop for minimal drag, but this is where they will not be needing traction.

Cup is a curl on the following edge of the blade to prevent slip. This is to help prevent slip or cavitation. The more cup the less slip, ie the harder the prop holds on to the water.

Material ss vs brass vs nibral. Brass has typically been the easiest material to work with and the cheapest. So traditionally that is what props were made of. Then for performance ss came along to eliminate a large portion of the slip. Traditionally these were uses for racing. Then came nibral which is a composite metal of brass/nickel/and aluminum. Aluminum has traditionally been what io props have been cast of. Nibral lies between brass and ss, but cannot be molded, it must be machined to get a very smooth powerfull prop.

Cup can affect rpm's slightly by eliminating slip, but only slightly. If you want to move rpm's significantly like you are talking about, I believe that you need to increase pitch. If you want to increase your cup you might not have to increase pitch as much, but I think that you still will.

Keep us informed with what way you go with all of the dimensions. It will be interesting to see what you like the best.

Good luck

Thumbup.gifThumbup.gifThumbup.gif

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areamike

More confusion. You guys are relentless... Cry.gif

So you are saying as others have that I need a little higher pitch say a 13x14 in order to decrease my WOT RPMs.

That contradicts what Max says with the 13x12 or 12.5.

Bottom line is I want to decrease WOT RPM. And my current prop is a stock SS 13x13 3 blade. Don't know what cup it is.

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NorCaliBu
More confusion. You guys are relentless... Cry.gif

:lol:

I would go with Max's recommendations. I can't remember...will skier-to-skier let you demo? If so, then pick one to start with and if it's not what you want...exchange it and try something else. Knowing how my 13X12 behaves I would tell you to try the 13X12.5 but what do I know... Crazy.gif

The variable is in the efficiency of the "push" of the prop. HBT mentioned the 13" of travel from one rotation of a 13 pitch. That is true but with the caveat that there is some slippage. With the larger blades of a CNC'd prop there is less slippage, more push. The CNC'd props are fairly new and "conventional wisdom" does not always apply...they are a different animal.

Good luck and keep us posted.

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hotrodbowtie

I will agree norcal. Lots of variables. I was just trying to pass along some knowledge. I need to start up that prop database again. I lost it all in a network crash.

:) :) :)

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