Prop

[Cusefan78]

So all this prop talk got me thinking. I'm running a 4 blade 13x13 on my labrisa. Noticed a small bend on the very end of the prop this weekend. I'm not getting any vibrations or loss of Speed/ hole shot. I use my boat for skiing 90% of the time. I decided to get another prop and wanted to get everyone's advice on what to get. My plan is to send my old prop out to get repaired after I get a new one.

[cadunkle]

Current max RPM and MPH would help as well as RPM at your typical ski speed along with any areas your not currently satisfied with the performance (want better hole shot, higher top speed, lower RPM at your usual speed, etc.). Your current pitch is in the ballpark of what should be good all around. You might consider going to a 3 blade if you primarily run at slalom speeds as it may get you a little better top speed or slightly less RPM at slalom speed with otherwise similar performance. I'm no prop expert though.

[Cusefan78]

Top speed is 48 mph And that's at 4300 Rpms. Performance is great. Hole shot is good, plenty of torque. I always throught 3 blades would give you more top end but would lose on hole shot. Am I wrong? I like the performance I have now and don't want to get 50 mph boat and lose any hole shot.

[Wulphie]

I am guessing you have a 1to1 trans, looks like about 9% prop slip if that speed is accurate. That is pretty good.

Check your prop slip numbers at say 2500 rpm, 3000 rpm and 3500 rpm

I am waiting on a 4 blade to try on my boat because my prop slip numbers are horrible in the mid range with the 3 blade I have.

[Cusefan78]

Which three blade are you using. Nettles suggested an acme 541

[Wulphie]

541 is for left hand rotation, I wouldn't get very far with that hahaha! My setup is rh rotation and I am not sure of the exact model of prop I have, but the combination of 12" of pitch and I think I calculated over 20% slip my rpm is way to high. It was running around 3750 rpm at 31/32mph gps. I have a 13x13 4 blade on the way, it should get me where I want to be.

[cjtpilot]

When I talked to ACME they recommend the 3-blade Acme 1442 (13.25 x 15 .090 cup) R 1" bore for my boat. Waiting until this winter for the upgrade though.

[Cusefan78]

Man this prop thing is a pain in my you know what. There are so many options and I can't make a choice. I wish there was a company that would let me try a few of them then buy the one I want. So frustrating

[cadunkle]

4 blade should have less slip, and grip better on hole shot so long as you have the torque to turn it. This can mean lower fuel consumption at slower speeds and potentially greater acceleration.

8% slip is very good for an inboard with a steep shaft angle at high speed. My original 14x13 3 blade cast OJ I was getting 22% slip. My 13x12 3 blade CNC Acme seems to be 21%. My Saltare probably weighs twice what your Comp does and has a lot more surface area to cause drag so that could account for a large part of that difference.

Anyhow I'd be tempted to try a 3 blade CNC 13x13 and see what kind of top speed you get. I'd expend a couple more MPH and maybe 200 RPM more. Or if you prefer a 4 blade try dropping an inch of pitch which may have a similar result. Or keep that prop and work on more power, goal being to spin that prop into the 4500-5000 RPM range at WOT. Either way I'd be shooting for a few hundred more RPM wide open.

[Wulphie]

Cadunkle is basically right on. The only thing I would add is that a lower rpm doesn't always use less fuel, you would have to consider engine load to. Using extreme examples you could have a 3 blade with more prop slip, a higher rpm but have less engine load and use less fuel or a 4 blade with less prop slip, lower rpm but heavy load and use more fuel.

In my case the 3 blade I have with a lot of slip does not put a lot of load on the engine so while I am turning 3,750 rpms at 31/32 I am not really into the throttle much. I would not be surprised if the 4 blade I have coming will put a little more load on the engine even though it will be turning a lower rpm with less slip. I just really don't want to sit next to my 454 with is screaming at near 4,000 rpm all day hahaha.

[Cusefan78]

I have to say torque and power is not a problem at all. I have a labrisa which is a lot heavy then a comp. what I have been told by nettles is the new cnced 3 blades are much more efficient then the old 4 blade cast props. I have had two company's all tell me to go 3 blade 13x12 which will give me better hole shot and better too end. The prop slip you guys are talking about is way over my head. I have been looking for a 4 blade 13x13 cnc prop but keep coming up empty. So I guess I'm lost. I may by two different props and find out what works better and send the one that doesn't back. Nettles does a 30 day money back gaurentee.

[Wulphie]

Think of it this way, the more surface area of the prop the more "traction" it will get, less slip. The less surface area the less "traction" and more slip. But the surface also adds more friction in the water so it can put more load on the engine. It would be like putting monster truck tires on and going to the bonneville salt flats, you might get good traction but the rolling resistance will not give you good top speed. Some pizza cutter tires will get a lot less traction but the lower rolling resistance will give you better top speed. It is really the same idea with a prop. There is other factors when you consider water but those aren't as important when talking props on a ski boat.

[Cusefan78]

Okay that makes sense. But why are people telling me a new cnc prop that is 3 blades better then an old cast 4 blade. Seems like the surface area would get me out of the hole quicker but from what everyone has said the new 3 blades will get me better hole shot and top end. This is what I'm confused about.

[Jetlink]

Because the new CNC 3 blades have almost the same surface area of the old cast 4 blade props yet they are made to closer tolerances and you have inherently less drag from a 3 blade prop versus a 4 blade prop. In a sense you get the hole shot of a 4 blade without losing the top end that a 3 blade prop allows.

[Cusefan78]

Thanks jet. Think I'm going to go with the 541

[Wulphie]

If you look at the new 3 blades the have a lot of surface area compared to the older props.

The key to a cnc prop is the fact that a machine will have great repeatability. It will be able to make 1000 props all to exacting tolerances.

To keep it simple, a little slip can be a good thing to allow your engine to get into the meat of the power curve.

To get a little more complicated. If you dip your hand in water there is very little resistance, the faster you move your hand through water the more resistance you will encounter. With that being said, when you turn a prop in the water slowly and the boat is moving slowly there is little resistance so there tends to be more slip. The faster the blade turns and the faster the boat moves the more resistance and the more grip and less slip the prop has. So when you apply that to a small block that has a torque peak higher in the rpm range you want the prop to slip at lower speeds to get the rpm up then it will naturally get more grip because the prop speed and boat speed are higher. If you start with a lot of grip the engine may not have enough torque at low rpms to get into the meat of the power. This is the reason they use 1.5 to 1 transmissions, to lower prop shaft speeds and use higher pitch props, because then you actually have more slip. Some of this theory does get messed up on a ski boat because of the angle of prop shaft in relation to the angle of travel.

Here is an extreme example of a lot of prop slip at low speeds that helps to achieve high speeds but terrible hole shot. and notice how the slip goes down as sped increases even though the props are more than half out of the water. . . https://www.youtube.com/watch?v=Of1RY4M8VqM

[lively]

If you look at the new 3 blades the have a lot of surface area compared to the older props.

The key to a cnc prop is the fact that a machine will have great repeatability. It will be able to make 1000 props all to exacting tolerances.

To keep it simple, a little slip can be a good thing to allow your engine to get into the meat of the power curve.

To get a little more complicated. If you dip your hand in water there is very little resistance, the faster you move your hand through water the more resistance you will encounter. With that being said, when you turn a prop in the water slowly and the boat is moving slowly there is little resistance so there tends to be more slip. The faster the blade turns and the faster the boat moves the more resistance and the more grip and less slip the prop has. So when you apply that to a small block that has a torque peak higher in the rpm range you want the prop to slip at lower speeds to get the rpm up then it will naturally get more grip because the prop speed and boat speed are higher. If you start with a lot of grip the engine may not have enough torque at low rpms to get into the meat of the power. This is the reason they use 1.5 to 1 transmissions, to lower prop shaft speeds and use higher pitch props, because then you actually have more slip. Some of this theory does get messed up on a ski boat because of the angle of prop shaft in relation to the angle of travel.

Here is an extreme example of a lot of prop slip at low speeds that helps to achieve high speeds but terrible hole shot. and notice how the slip goes down as sped increases even though the props are more than half out of the water. . . https://www.youtube.com/watch?v=Of1RY4M8VqM
Man that's a lot of roost to board behind ! Need one hell of a goggle set up and maybe on board air system ! Lol

[Wulphie]

I know haha! isn't that setup outrageous! It is such a great video because you can really see how the props work and hear the engine rpm flare with the slip until the boat gets going.

I have never been on a boat with surface drives and I was surprised to see that even the shafts come out of the water. I was talking to the mechanic at the shop where I bought my 454 and he has driven boats with surface drives and he said they have a very strange floaty feel to the stern. Wild stuff.

[Cusefan78]

Well I did it. Just bought an acme 541 of team talk for $310. Only been used a handful of times. Thanks everyone for the help. I'll report back next week on the performance. I read on here I should lightly heat the prop and give it a whack with a deadblow. Is this the best way? Also who does everyone recommend for getting the old prop repaired.

[Moor]

Well I did it. Just bought an acme 541 of team talk for $310. Only been used a handful of times. Thanks everyone for the help. I'll report back next week on the performance. I read on here I should lightly heat the prop and give it a whack with a deadblow. Is this the best way? Also who does everyone recommend for getting the old prop repaired.

i put an ACME 541 on my sunsport 2 weeks ago, it was THE BEST decision i've made in a long time. put it on and don't look back. i was running a 13x13 O.J that looked like it hadent been off in a long time. I used a crappy 3 jaw puller to put a little pulling force on the prop, a very little bit of heat from my map gas torch, and 2 light whacks with a hammer and 2x4 and she popped right off. Since this word to the wise was passed on to me 2 weeks ago, its only proper to share: be sure to lap the new prop to the shaft before you install the new prop. let us know how you make out

[Cusefan78]

What did you use to lap it. HVe heard rubbing compound and also valve paste

[Moor]

I used prussian blue and valve grinding compound that i had lying around from previous projects. Both are availanle at napa for a few dollars each.

[Cusefan78]

Perfect I'll give it a try next weekend. Any tips to getting the old one off without a puller

[92SupraComp]

Heat, a bfh, and some more heat... But really, you need heat and a puller.

[Cusefan78]

Will a three jaw puller work. Have a pretty big one up at the cottage

[SquamInboards]

I have used one of those, but it can be tricky to get the three arms lined up and to get a good grip on the prop. But it's worth a try if you've got one already!

[wotan2525]

Map gas and a rubber mallet or a leverage 2x4 has always worked for me. I'm not usually worried about not damaging the one coming off, though.

[Cusefan78]

Yeah I'm not worried about this one. Needs to get repaired anyways. It's the original 4 blade oj.

[Moor]

Map gas and a rubber mallet or a leverage 2x4 has always worked for me. I'm not usually worried about not damaging the one coming off, though.

i used a 3 jaw puller that wouldn't quite line up nice. i tightened it as much as i could before it popped off to put some pulling tension on the prob, used a little heat from my map gas torch, and a few solid whacks with a hammer and 2x4 on the back side of the prop, should pop it right off. be careful, the prop may be hot depending how much heat u put into it. bronze heats up pretty fast, so you prob wont need much heat.

[Cusefan78]

I have a two jaw and three jaw puller I'll bring up with me this weekend thanks for all the advice

[Cusefan78]

Finally got my 541 on. Wow what a difference. 51 mph and better hole shot. Also I have almost zero vibration now. Huge difference. Thanks everyone for the help

[SquamInboards]

Finally got my 541 on. Wow what a difference. 51 mph and better hole shot. Also I have almost zero vibration now. Huge difference. Thanks everyone for the help

I wish we could get Acme to pay us for all these reviews. I firmly stand by my statement that replacing an old cast prop with a CNC is the single best "performance mod" you can make to an old ski boat.

When you get a chance, fill in some info on the Prop Specs thread...

[Cusefan78]

I will. I wish I had a video of my girlfriend flying out of her seat when we went for a test run. Priceless.

[SquamInboards]

haha, amazing. I've sent my wife (then girlfriend) pretty hard against the little opening to my bow area, "testing" the new steering cable (doing a powerslide without warning). She hit her head pretty hard and was not amused at the time.

[Cusefan78]

Ha I did the same last year when I did my cable. She was sitting on the back bench and slid all the way across and water came over on heard. She wouldn't talk to me for a day.