Understanding propellers

[rcuadro]

Ever since I bent my prop, I have started reading about propeller for the heck of it (it is slow at work) and, while I understand most of it, what gets me is the number of options available.

Take my boat for example. I have an 05 VLX and, according to wakeprops.com, there are 4 different ACME props they sell and I can use.

http://www.wakeprops.com/wakeboard-boat-propeller-finder/malibu-wakeboard-boat-propellers/

537: 13.5" x 16" (For Skiing, and I have this one on since it was my spare)

1941: 14.5" x 15" (For "everything")

1235: 14.5" x 14.25" (Wakeboarding and the one that I bent)

2315: 15" x 12" (high altitude)

I know this is a guideline since the prop you want really comes down to what you use your boat, number of people, location, how much extra ballasts you have. To keep it simple I will just use my boat and no real changes.

Anyhow, I understand what the numbers mean. The first number is the diameter of the prop in inches and the second is the pitch (the displacement per revolution) ie, the distance a propeller will travel assuming no slip. So a 13.5" x 16" prop is 13.5" round and will move forward 16" per revolution. Pretty simple.

Looking at all the props for my boat, why the change in prop size? I realize that you want to change the pitch to change the torque generated and to change your top speed, depending on how you want to use the boat... but how much does the prop size affect the thrust generated? Why is the ACME 537 a whole inch smaller than then 1941 and 1235? Why not just change the pitch?

As for high altitude, I am assuming that you need bladed with a larger surface area and not as an aggressive pitch dues to the lower oxygen levels in the air leading to lower power output from the engine.

So there ya go! That is what is running through my mind on a Thursday morning, while I should be working.

[formulaben]

Don't hesitate to call the folks at ACME! I found the call well worth my time. I talked to an engineer for well over an hour (I had to shut him up!) and he was more than helpful regarding prop choice for my boat. He knew the boats well and took the time to learn what I would be doing and where.

But most importantly, he explained what all the specs mean on a prop. I already knew what diameter and pitch would do, but cupping was a mystery to me. He explained that .050" cup was equivalent to 1" of pitch. That's huge. He also put me at ease in that the difference between the next prop down, which was mainly cupping. If I didn't like the performance of the prop, he could re-cup it to match my needs.

Good luck!

[rcuadro]

He explained that .050" cup was equivalent to 1" of pitch.

If I understand cupping correctly, cupping allows the prop to "grip" the water better but all that should do is bring he actual pitch to the theoretical pitch. And by that I mean reduce the amount of slip of the prop.

Though,perhaps, a .05" cup has the same effect as adding 1" of pitch since the prop blade will grip better

[nyryan2001]

rcuardo-- what prop do you have and what are you trying to do with your boat?

I can tell you that the folks at Acme are not always 100% on target with reccomendations.... i just went thru 4 props on my boat.... learned a ton about how they affect.

[Falko]

And that barely scratches the surface. Props are a magic all their own.

[rcuadro]

rcuardo-- what prop do you have and what are you trying to do with your boat?

Nothing specific. After I bent my prob and put my spare on I started thinking... "Why is this one a whole inch smaller than the other one?" and it snowballed into the hot mess you see in the fist post here.

[nyryan2001]

gotcha. here some prop talk:

here is a misnomer I learned thru my trials and errors... everyone tends to think the 1235 is a bigtime torque prop, likely somewhat compared to the 45mph prop that comes OEM on most boats.....but its really still in the mid range comparatively. in the 14-14.5" dia props.... its really in the middle torque wise because it still has so much pitch.

Give it 5yrs and the word get out some, even on the smaller 21ft boats with 350s... will be on the 15" 2315 as the new "torque" prop for the guys looking to sac out heavy for wakesurfing and at 22mph.

Folks at Acme and other places are considering larger than 15" props now.

[rcuadro]

And that is what got me thinking about the size of the prop. With the given prop size remaining constant, the less the pitch, the more torque (but less top speed)... addition of cupping to the blades decreases prop slip, giving you more speed and toque when you keep the prop size and pitch constant.

Would it be a good assumption that an increase in prop size, while keeping pitch and cupping constant, give you more torque and speed due to the larger blade surface area?

[Brad B]

The 1235 is a bigtime torque prop - as compared to the OEM 537.

We regularly use over 3k lbs of ballast and the 1235 has turned out to be the perfect prop for us - your milage may vary but I've seen the same results on several other boats in our armada of Malibus and Supras

[Fman]

gotcha. here some prop talk:

here is a misnomer I learned thru my trials and errors... everyone tends to think the 1235 is a bigtime torque prop, likely somewhat compared to the 45mph prop that comes OEM on most boats.....but its really still in the mid range comparatively. in the 14-14.5" dia props.... its really in the middle torque wise because it still has so much pitch.

Give it 5yrs and the word get out some, even on the smaller 21ft boats with 350s... will be on the 15" 2315 as the new "torque" prop for the guys looking to sac out heavy for wakesurfing and at 22mph.

Folks at Acme and other places are considering larger than 15" props now.

Seems like you are comparing an apple and a orange? You have a 10k + lb boat, a VLX weighs much less than this... a 1235 on your boat is much different than a 1235 on any year VLX. It does not surprise me you did have to experiment with multiple props, because of the massive weight of your boat.

I have been running a 1235 for years, it seems to be much better torque than the 1939 malibu puts on standard. Factory ballast, wedge and another 1200 lbs the 1235 always pulls great with the Monsoon 350. I also like the 1235 because it allows you to still pull a slalom skier at 32-34 mph.

[jk13]

Re: diameter. There have been some issues on other sites where using too large of a prop has been causing issues. The closer the prop gets to the gel coat on the bottom of the boat the greater the risk of turbulence/air bubbles/cavitation actually eating away at the gel causing pitting. MC X30 from a few years ago was a known one.

Just be careful not to go too big.

It has also been explained to me that more cup is to lower the engine RPMs when using a lower pitch prop to keep the motor off the rev limiter. You get the benefits of lower pitch for pulling, the draw back of less top end, but it lowers the RPMs.

[PyleDriver]

In I/O the cup can change the way the prop loads the boat. It can effect if you have bow or stern lift.

I would assume the same physics would be at play in a V drive but I have no idea

I know cup does more then act as a pitch change.

This is all very interesting since I am looking for a new prop. I have a 1235 and don't need that aggressive of a prop at lower altitudes.

Mike

[srintx]

In I/O the cup can change the way the prop loads the boat. It can effect if you have bow or stern lift.

I would assume the same physics would be at play in a V drive but I have no idea

I know cup does more then act as a pitch change.

This is all very interesting since I am looking for a new prop. I have a 1235 and don't need that aggressive of a prop at lower altitudes.

Mike

I agree Mike, I'm looking for a new one as well to potentially try to increase the surf wake. It looks as if the 1235 maybe the best fit.

[nyryan2001]

Brad/ Fman-

Yep no doubt 1235 is more torque than OEM. No dispute there.

What I am saying is there are 8-10 props avail that are torque-ier than the 1235 available, and will still get you in the high 30s. And when I Say more torque, I am saying 3-6 seconds faster to 22mph. That's a huge difference.

I did back to back tests... With the 2249. Basically it's the 15" equiv of the 1235, same specs, only 1/2" bigger.. I was able to plane sac'd out a full 5 seconds faster going to the 2315. 19 seconds avg with the 2249, 14 seconds with the 2315. 7000boat + 3000 OEM ballast. We are a talking 25-30% faster?

What I am getting at is for all you guys who carry the big weights, and don't care about going 40+ mph... There are a lot better props out there than 1235 to get you to 11.5 for surf or 22mph.

Brad, I can tell you that you can likely shave 3-4 seconds off your 0-22mph with your 3k over OEM ballast by dropping pitch. It's THAT big of a difference. Or add another 1000lbs and keep the same performance you see now.

And for the folks worried about clearance... 1235 is 14.5dia. Going to a 15" is a 1/4" closer to the hull. What Malibu can't support that?

You heard it here. Give it 2yrs and folks will be talking about the 2315s like they have the 1235s for the last 5yrs. 2315 will truly turn a wakeboat into an F350.

Not trying to start a piss war over 1235s not being great props... They are, and still well rounded. It's just that you can get your 3k over OEM up to 22 3-5 seconds faster if you are ok with a 37-39mph boat on a 15" prop.

Wait till the guys with 21-23 LSVs with 350s start posting up their results on there. It's a good time to be selling 15" props.

[rcuadro]

I agree Mike, I'm looking for a new one as well to potentially try to increase the surf wake. It looks as if the 1235 maybe the best fit.

I think it all comes down to personal preference and what you want to do with your boat. I am new to boats and I bought mine used with a 1235 on it so I have nothing to compare it to. When looking for a spare prop, the price I paid for the 537 was too good to pass up and, since I wanted it for a spare, the money saved was well worth it for me.

At the current time, top speed or the holeshot, mean nothing to me since we are at a learning phase. Not to mention most of the kids would rather tube than anything else.

[Fman]

Brad/ Fman-

Yep no doubt 1235 is more torque than OEM. No dispute there.

What I am saying is there are 8-10 props avail that are torque-ier than the 1235 available, and will still get you in the high 30s. And when I Say more torque, I am saying 3-6 seconds faster to 22mph. That's a huge difference.

I did back to back tests... With the 2249. Basically it's the 15" equiv of the 1235, same specs, only 1/2" bigger.. I was able to plane sac'd out a full 5 seconds faster going to the 2315. 19 seconds avg with the 2249, 14 seconds with the 2315. 7000boat + 3000 OEM ballast. We are a talking 25-30% faster?

What I am getting at is for all you guys who carry the big weights, and don't care about going 40+ mph... There are a lot better props out there than 1235 to get you to 11.5 for surf or 22mph.

Brad, I can tell you that you can likely shave 3-4 seconds off your 0-22mph with your 3k over OEM ballast by dropping pitch. It's THAT big of a difference. Or add another 1000lbs and keep the same performance you see now.

And for the folks worried about clearance... 1235 is 14.5dia. Going to a 15" is a 1/4" closer to the hull. What Malibu can't support that?

You heard it here. Give it 2yrs and folks will be talking about the 2315s like they have the 1235s for the last 5yrs. 2315 will truly turn a wakeboat into an F350.

Not trying to start a piss war over 1235s not being great props... They are, and still well rounded. It's just that you can get your 3k over OEM up to 22 3-5 seconds faster if you are ok with a 37-39mph boat on a 15" prop.

Wait till the guys with 21-23 LSVs with 350s start posting up their results on there. It's a good time to be selling 15" props.

Thats great information, I am pretty amazed a prop can be that much better than the 1235 and still give you top speed of 39 mph. Are the RPM's different while wakeboarding at 22mph between the two? Assuming you would burn more fuel? or maybe not?

[Bawshogg]

2315 for me. ! Who surfs at 40mph anyways?

[shawndoggy]

Acme 2079 is the 1235 (14.5 diameter) in a 12 pitch. That's definitely going to snap some necks out of the hole on smaller boats.

[gorilla]

Well, I just put on my 1273 today. I wanted the hole shot of the 1235 with a bit less rpm at foiling speeds. Plus, sometimes it felt like the 1235 would cavitate when taking off hard with full ballast for surfing. I read that the extra cup can help that. I spoke with Acme and they said 2249 or 1273. I am hopefully gonna be able to test it Monday, but don't know for sure. I didn't want to go down in pitch because I am already turning 3k+ at foiling speeds.

[rennis]

In I/O the cup can change the way the prop loads the boat. It can effect if you have bow or stern lift.

I would assume the same physics would be at play in a V drive but I have no idea

I know cup does more then act as a pitch change.

This is all very interesting since I am looking for a new prop. I have a 1235 and don't need that aggressive of a prop at lower altitudes.

Mike

We should trade props

Sent from my iPad using Tapatalk HD

[wakesetter8796]

Brad/ Fman-

Yep no doubt 1235 is more torque than OEM. No dispute there.

What I am saying is there are 8-10 props avail that are torque-ier than the 1235 available, and will still get you in the high 30s. And when I Say more torque, I am saying 3-6 seconds faster to 22mph. That's a huge difference.

I did back to back tests... With the 2249. Basically it's the 15" equiv of the 1235, same specs, only 1/2" bigger.. I was able to plane sac'd out a full 5 seconds faster going to the 2315. 19 seconds avg with the 2249, 14 seconds with the 2315. 7000boat + 3000 OEM ballast. We are a talking 25-30% faster?

What I am getting at is for all you guys who carry the big weights, and don't care about going 40+ mph... There are a lot better props out there than 1235 to get you to 11.5 for surf or 22mph.

Brad, I can tell you that you can likely shave 3-4 seconds off your 0-22mph with your 3k over OEM ballast by dropping pitch. It's THAT big of a difference. Or add another 1000lbs and keep the same performance you see now.

And for the folks worried about clearance... 1235 is 14.5dia. Going to a 15" is a 1/4" closer to the hull. What Malibu can't support that?

You heard it here. Give it 2yrs and folks will be talking about the 2315s like they have the 1235s for the last 5yrs. 2315 will truly turn a wakeboat into an F350.

Not trying to start a piss war over 1235s not being great props... They are, and still well rounded. It's just that you can get your 3k over OEM up to 22 3-5 seconds faster if you are ok with a 37-39mph boat on a 15" prop.

Wait till the guys with 21-23 LSVs with 350s start posting up their results on there. It's a good time to be selling 15" props.

We ski at 35 occasionally, so would you recommend the 1235 or 2315? We just have oem ballast and lead right now but will add more later.

[srintx]

2315 for me. ! Who surfs at 40mph anyways?

I'm running the 1939 and can barley get over 10mph with the boat loaded with stock and extra ballast...Bobby are you running the 2315 on your boat?

Has anyone else experienced this with the 1939? Would the next best fit be the 2315 or the 1235?

[gorilla]

well, tried out the 1273 today......works great!!! my hole shot seems the same with and without ballast as the 1235, but my foiling speeds (21-26mph) sees a nice drop in rpm. no increase in spray at speeds, no change in surfing wave. love it so far........

[shawndoggy]

I'm running the 1939 and can barley get over 10mph with the boat loaded with stock and extra ballast...Bobby are you running the 2315 on your boat?

Has anyone else experienced this with the 1939? Would the next best fit be the 2315 or the 1235?

1235 on a vlx would be money for all but the most hardcore. I'd be interested to hear how well a monsoon will spin up a 15" prop. I'd think the 2079 would be better suited for a vlx but I'm not a propologist.

[Fman]

I'm running the 1939 and can barley get over 10mph with the boat loaded with stock and extra ballast...Bobby are you running the 2315 on your boat?

Has anyone else experienced this with the 1939? Would the next best fit be the 2315 or the 1235?

I had the 1939 on my '11 VLX, used it for 6 hours and put a 1235 on and never looked back. The 1939 imo was terrible... I run full mls, wedge, 1200 lbs bags for surfing and the 1235 is great... also good for wakeboarding full ballast, and you can tow a slalom skier at 32-34 mph.