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vette-ski

Understanding prop sizes

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vette-ski

I'm just looking to get an understanding of how different prop sizes will affect performance of my SS VLX. I've been keeping an eye on e-bay and the classifieds for a cheap spare to keep in the boat. I don't think I'll find my exact size (13.5x17.5 4 blade), so I'm just curious how props will slightly different numbers will compare.

I'm pretty sure I understand the last number (pitch). Essentially a larger number = higher top speed, lower number = better out of the hole. But what about the diameter? Will I see any noticible difference between a 13 or 14"? And what about 3 blade vs. 4 blade?

As an example, there are two on e-bay right now: a 14x18 3 blade OJ, and a 13x18 4 blade SS. Thoughts?

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doughickey
I'm just looking to get an understanding of how different prop sizes will affect performance of my SS VLX.  I've been keeping an eye on e-bay and the classifieds for a cheap spare to keep in the boat.  I don't think I'll find my exact size (13.5x17.5 4 blade), so I'm just curious how props will slightly different numbers will compare. 

I'm pretty sure I understand the last number (pitch).  Essentially a larger number = higher top speed, lower number = better out of the hole.  But what about the diameter?  Will I see any noticible difference between a 13 or 14"?  And what about 3 blade vs. 4 blade? 

As an example, there are two on e-bay right now:  a 14x18 3 blade OJ, and a 13x18 4 blade SS.  Thoughts?

Here's 2 websites that will help a lot with the info you're looking for.... and BOTH places have great guys that will talk with you directly.

SS is very strong, hard to damage. Downside is that if you hit something, it might be your shaft or tranny that suffers.

Nibral (Nickel/Brass/Aluminum) is much softer, damages easier. Although they can repair, I hear (no personal experience) that sometimes the repairs don't quite bring it back to 100%.

The ACME and OJ Ninbral props are NC milled. (Numerical Controlled) This means they are cut EXACTLY as designed for perfect balance. Other props are cast, so there could be minor shape changes as thhe molten/heated metal cools.

Generally 4 blades give a more consistent pull. Good for when you board with lots of weight in the boat. Generally the added blade surface also adds more blade-to-water surface contact.... so more fluid drag... so less top end.

However, OJ (and possibly ACME) seem to have solved this downside by designing 3 blades with larger surface areas. Same pull as a 4 blade without the 4 blade downside.

Generally, 1:1 transmissions use pitches in the range 11.5" to 14". Some boats (like Mastercrafts) have transmissions (like the Powerslot) that have a 1.6:1 ratio. This means that it takes 1.6 motor revolutions to spin the drive shaft (prop) once. This means they can use pitches in the range of 15" to 17".

Most Malibu's have a 1 1/8" drive shaft. Many other boats are only 1". If you do buy used, make sure you get a prop with the correct size shaft.

Malibu also uses LEFT HAND rotation. CorrectCraft is RIGHT HAND rotation. Make sure you get the correct rotation.

Some props use "splines" to connect with the drive shaft. Others use "shaft keys" (small rectangular blocks that slide into a squared groove in the prop and the drive shaft.) Make sure you get ones that match.

If you have an OEM (Original Equipment Mfg) prop on your boat that is SS, it may be the old CVP (I think this is Credit Valley Propeller from Caliifornia). They are no longer in business. Smaller blades. Rumor has it that some had blades that cracked. Smaller blades. It's what I have on my 1998 RLX. However, these can get prop burn.... or airation (some call it cavitation) that causes pitting on the blade surfaces. This is when the blades (on take-off) spin so fast that the negative pressure on the front side causes the water to "boil" and become water vapor. Somehow this vapor can get sucked around to the back side... hits higher pressure... and IMplodes, causing the pitting of the blades. (See picture). I used this "safety" concern to convince my wife we needed a new prop. So, I just received my new OJ XMP prop.... haven't even tried it yet. Apparently, these props have a larger surface area.... so less "spin", more bite, no airation, no pitting, no cracks, smoother performance, better pull, bigger smile on my face, smaller bank account balance.

http://www.acmemarine.com/html/tech.html

http://www.skiertoskier.com/

Try Eric at ACME, and Max at Skier-to-Skier.

Since you can get a NEW prop (either ACME or OJ) these days for $300 or a few bucks more, I'd be real nervous about picking up a used one off of e-Bay... unless it was dirt cheap.

Good luck on your information and prop quest. It can be a jungle.

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martho

Good info Doug!

If you have an OEM (Original Equipment Mfg) prop on your boat that is SS, it may be the old CVP (I think this is Credit Valley Propeller from Caliifornia). They are no longer in business. Smaller blades. Rumor has it that some had blades that cracked.

It is not rumor. It has happened to several people. I have seen it first hand on a buddy's boat.

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WakeGirl

Very good info Doug, I'll just add one thing to the mix. When I was searching for a different prop for my boat, I spoke with Jim at Acme several times (I would highly recommend this, he's very knowledgeable & willing to help). One thing that he told me is that for every 1/2" in pitch (second number) that you go down in size, you'll increase your overall rpms by about 200 (as an example, we were hitting about 4800-900 with the stock 13x12.625" prop, going to a 13x11.5" prop we see 5400 at WOT now). So you definitely need to know what the rpm you're hitting at WOT is without ballast, extra people or gear in the boat to use as a starting point. One other thing, you can't cross over & try to compare a 3 blade directly against the same sized 4-blade - the ratios are different.

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UWSkier

What are you planning on using the boat for primarily? With the V drive, I'd stick with the CNC 4 blade props. Those really do give the best performance. If you wakeboard a lot, get the 13.5x16. It'll suck gas bigtime on the top end and probably hit the rev limiter, but it'll hold speeds really well at wakesurfing and wakeboarding speeds, and it'll handle a heavy ballast load better. If you're not going to run a ton of ballast and spend a lot of time at cruising speed and/or pulling slalom skiers and barefooters, stick with the 13.5x17.5.

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vette-ski

I slalom. Every once in a great while a buddy will bring a board. Mainly I just wanted to have a spare prop on hand. But I also wanted something that I might actually use. I went with the 13/18 SS 4 blade on e-bay. At a fraction of new cost, I figure I can't go wrong. If I don't like the performance, I'll keep it under the seat as an emergency spare.

Thanks for the tips everyone.

Edited by vette-ski

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obski

You should make sure you put it on and try it out when you get it to see if it really usable by you on your boat.

I bought a nibral 14x18 3-blade prop a year or so ago to use as a spare and had never tried it out. I dinged up my prop while at the NW WOW last weekend and decided to spring for a new 'wakeboarding prop', the Acme 537, since that is what we do mostly. I sent my stock 381 back to Acme for repair. The 537 is on its way, but won't be here until Monday, so I thought I would try out the spare I had and then decide whether or not to sell one of the props. I picked up an Ironman prop puller kit from Elberts, which is awesome by the way, and swapped out props.

I took the boat out on the water last night and found that it has absolutely no hole shot. It's kind of like when I had a Datsun 210 and was trying to go up a steep hill. There's nothing there. Once it finally gets up on plane it is just fine. I'm used to the boat responding immediately to throttle. I could pull kneeboarders just fine, but not wakeboarders. I was trying to pull up inexperienced boarders. I'm quite sure my daughter who is much lighter and much better at wakeboarding could have done it, but I still wouldn't have been using ballast or wedge.

The spare prop is clearly inadequate and I think pretty much useless as a spare for me. I'll be selling it soon. Anyone need a 14x18 3-blade?

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Jimmy Buffett

14x18 is like starting out in 4th gear.

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NorCaliBu
Anyone need a 14x18 3-blade?

After your glowing review on it's performance? :lol: Good luck. :)

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obski
Anyone need a 14x18 3-blade?

After your glowing review on it's performance? :lol: Good luck. :)

Yeah, I didn't try to sell it here, but did put it up for sale on e-bay. It's got a day to go and it will already sell, but I did set the starting price low at $80. I looked the prop up on some on line prop sites and found that the same prop (same make and model) sell for $310 to $350 on their discount sites. I'm sure it is a good prop for the proper application, which I think was originally for a Mastercraft model - not sure which one though. It just wasn't a good prop for my boat. Oh well, I didn't pay too much for it and now I will have a proper spare.

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vette-ski
14x18 is like starting out in 4th gear.

Is there really that much difference in 1/2-1 pitch size? Are you thinking maybe for a direct drive? The stock prop on my v-drive is 13.5x17.5. Or is there really that much noticeable between a 14x18 3 blade vs. 4 blade?

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obski
14x18 is like starting out in 4th gear.

Is there really that much difference in 1/2-1 pitch size? Are you thinking maybe for a direct drive? The stock prop on my v-drive is 13.5x17.5. Or is there really that much noticeable between a 14x18 3 blade vs. 4 blade?

There really is that much difference. The analogy of how it is like starting out in 4th gear is pretty much dead on. Once I got up to speed on plane it ran just fine and at a lower rpm. I was impressed with what a difference it made. My stock prop was the Acme 381 (4-blade 13.5 x 17.5) on my v-drive. I'm going with the Acme 537 (4-blade 13.5 x 16) and am hoping for some improved hole shot. Not that it was bad before, but there was some lag when fully weighted. I'll post my impressions after trying it out.

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vette-ski

3 blade vs. 4 blade difference? It's still confusing to me. If going from a 17.5 pitch to an 18 pitch is like starting in 4th gear, then I'm imaging going from a 17.5 pitch to a 16 pitch would lose tons on top, which may not be of any importance to you.

Reason I'm asking is the ebay 13x18 prop I got ended up being a mistake and I have been refunded. Turns out when it showed up it was really a 13x18.5. I tried it, and it was terrible. I had no throttle response from about 2/3 throttle to wot. Boat topped out a 36 mph, vs. 45 w/ the 13.5x17.5. The other factor is the diameter. Even though it was only marked 1/2" smaller, it measured a true 1" smaller. So I'm just trying to figure out if there was something wrong with the prop, or if it was just a terribly wrong mismatch for my boat. Either way, I have been refunded because it was advertised wrong.

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UWSkier

There's more than just pitch that will effect your throttle response. There's also cup and rake (which is pretty much nil on inboard props). The 381 and 537 are pretty much identical in this regard with the only difference being the pitch. You will lose 2-3 MPH on top with the 537, but it won't be a huge difference like going with an entirely different manufacturer that uses a different blade shape.

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