XMP- 12 or 11.5- need advice

[VinRLX]

Based on everything you've described.... I think the 11.5" is better for you.

Although your motor has a rated HP of 320 or 325 or 330 or so (assuming EFI Monsoon), it's currently not able to get enough revs to put out that HP.

<{POST_SNAPBACK}>

It would be 320, 325, and 335. His year (assuming Monsoon) 325. And the 11.5 would definitely give you more grunt.

[Lakenut]

By the way..... do you notice any "prop burns" on the blades of your CVP.

No cavitation burns just a small hairline crack about 1/3" long at the front of the root edge of one of the blades.

I was thinking the same thing about the 11.5 but if the 12 truns basically the same WOT what is the difference? 4950 WOT would be an increase of 150 rpms over what I get now.

[doughickey]

A couple of things.

If you're running 4800 rpm with the 13" CVP, you're still not getting all the HP out of your engine. (HP is a formula that includes Torque X RPM.) Your boat loaded the way it is just isn't taking full advantage of it's potential torque and HP if your'e maxing out at a low 4800 rpm (vs the rated HP at 5200 rpm), then you can get better performance by running a flatter pitch prop.

The OJ has more blade surface. So, it will be even harder to turn if you got a 13 X 13 straight replacement. (It will push more water..... be more efficient... less slippage). So, with the SAME 13" pitch, my guess is you'd drop even lower on the rpm's.... probably 200-300 rpms. Again, not taking advantage of the power available.

I think you might even find that if you used the 13" X 12" OJ, your rpm's still may be less than what you're currently running. You actually want to get a bit higher in the rpm range at WOT. Why.....

At boarding speeds (18 mph range), you will be running much slower. You want more grunt...more usable torque. The flatter pitch will give you that.

For skiing, you want 34 or 36 mph. (Maybe less). In your case, you can handle the flatter pitch.

Then again..... just buy one... try it out.... and swap it if it's the wrong one. I suggest trying the 11.5" first.

[Lakenut]

What would the 11.5 do to my fuel consumption vs. the 12? Also, the 11.5 would cause the engine to turn more RPMS thus the engine would not have to work as hard at skiing and boarding speeds? Right?

[kbtheboz]

I haven't noticed any drop in HPG or however you want to measure fuel consumption. There are too many variables to get an accurate measurement, skiing, boarding, tubing, cruising, loaded, empty, etc.

My "feeling" is that it would be the same or better, with the more efficient prop.

[CarveItUp]

What RPMs are you running at WOT with the new prop?

I haven't noticed any drop in HPG or however you want to measure fuel consumption.  There are too many variables to get an accurate measurement, skiing, boarding, tubing, cruising, loaded, empty, etc.

My "feeling" is that it would be the same or better, with the more efficient prop.

<{POST_SNAPBACK}>

[doughickey]

What would the 11.5 do to my fuel consumption vs. the 12?  Also, the 11.5 would cause the engine to turn more RPMS thus the engine would not have to work as hard at skiing and boarding speeds?  Right?

<{POST_SNAPBACK}>

Right. At boarding and skiing speeds, yes your engine will be turning a bit faster, but also probably into a better part of the torque curve.... hence not working quite as hard. Strong skiers or boarders won't be able to pull the boat speed down as much on hard cuts or wake-crossings.

Re fuel consumption. Tough to answer this one. Although you're spinning a bit faster.... you're running your engine a bit more efficiently... so could end up being the same gph (gallons per hour) .... maybe even better. Regardless which way it goes, the difference on gph between 11.5" and 12" I think will be negligible.

I keep records. Last year, over 53 hours, I averaged 2.72 Cdn Gal per hour. This is 3.4 US gal per hour. Combination ski/board/tour. This says I used 53 X 3.4 gallons = 180 gallons for the entire season. Assuming I had a prop that caused a 5% change (either way... up or down) in gph (gallons per hour), the difference in total gas usage over the entire summer would have been 5% X 180 gallons = 9 gallons. This is SO insignificant compared to anything else I spend money on. Assuming you do even double my hours per year, the savings/cost difference is so small compared to the added advantage of using your engine more efficiently... and compared to your entire boat expenditure.

The key thing is that you said your WOT rpm was at 4800.... much less than your engine is capable of. Propping down a bit will let you make better use of the power you've got.

[martho]

I keep records. Last year, over 53 hours, I averaged 2.72 Cdn Gal per hour. This is 3.4 US gal per hour. Combination ski/board/tour. This says I used 53 X 3.4 gallons = 180 gallons for the entire season. Assuming I had a prop that caused a 5% change (either way... up or down) in gph (gallons per hour), the difference in total gas usage over the entire summer would have been 5% X 180 gallons = 9 gallons. This is SO insignificant compared to anything else I spend money on. Assuming you do even double my hours per year, the savings/cost difference is so small compared to the added advantage of using your engine more efficiently... and compared to your entire boat expenditure.

5 tanks of gas all year. WOW! I am way more than 5 tanks in already and it is only the middle of June.

[Lakenut]

Man....If OJ just made an 13X11.75 my decision would be easy!!!!

[WakeGirl]

Have you contacted them to see if you can have one modified? I've seen talk of that in the past.

EDIT: I just got off the phone with Bill Weeks at Acme & they can either re-pitch or take a little cup out of the prop. He said that the re-pitch he really doesn't like to do on a prop that hasn't been damaged because it will never be the same as it was. But taking some cup out will allow it to spin/slip a little more allowing the engine to rev a bit more at the bottom, getting into its power band sooner. He said that taking some cup out wouldn't adversely affect the prop nearly as much as re-pitching. He quoted $150 for re-pitching, $45 for taking some cup out (going from .80 cup to .50 cup, on my stock 449 13x12.625, it would efectively make it perform like a 13x12). I'm running an Acme 525 (13x11.5) at medium to high elevation, & I'm concerned that dropping to near sea level will have me way over-revving with the 525. So I'm thinking about having the 449 re-worked.

Just something else to think about.

Edited June 13, 2005 by WakeGirl

[Lakenut]

Just something else to think about.

Thats what I need Tracie. More data. Acctually what I should do to get the best of all worlds is to buy an 11.5 and a 12 from oj. Then get an acme. Cut one blade off of each prop and use them to form an 13X11.5,12,12 acme/oj hybrid.

I just ordered a XMP 13X11.5. From everyone's data I think both props would be a step up from the ole CVP. With spending more time on the dark side I think the 11.5 will best suit our needs. I will definalty give some test results when I get it.

PS How long does it usualy take skier to skier to ship from their place to mine? I live in central OK. I am assuming 3-5 business days and I am hoping to have it for this weekend.

[edwin]

you should have your XMP before the weekend...unless there's no paved roads to your home there in OK

[doughickey]

Just something else to think about.

Thats what I need Tracie. More data. Acctually what I should do to get the best of all worlds is to buy an 11.5 and a 12 from oj. Then get an acme. Cut one blade off of each prop and use them to form an 13X11.5,12,12 acme/oj hybrid.

I just ordered a XMP 13X11.5. From everyone's data I think both props would be a step up from the ole CVP. With spending more time on the dark side I think the 11.5 will best suit our needs. I will definalty give some test results when I get it.

PS How long does it usualy take skier to skier to ship from their place to mine? I live in central OK. I am assuming 3-5 business days and I am hoping to have it for this weekend.

<{POST_SNAPBACK}>

I think you chose wisely.

I live in Canada. It was 15 calendar days.... but it had a US/Canada border to cross with all the fuss that they do re taxes etc. I also asked them to send just US Parcel Post (that way, I don't pay a X-border brokerage fee as well.) All that to say, you should get it in under a week. (Might be a stretch for a Friday delivery... but hope you get it.)

Looking forward to your results.

Once I get my replacement (12" pitch) prop, I'll post my results as well.

Fun spending money isn't it?

[Lakenut]

We have paved roads. Just got them last week.

[CarveItUp]

Time for some more information. I'm in the same boat as Lakenut (okay, one year older but still... ) and called ACME today. They recommended either the 525 (13 x 11.5 .080) or the 653 (13 x 11.5 .060) for our SLXi since we run at moderate altitude (3000 - 4000 foot elevation).

Our WOT is 4600 - 4700 according to PP on our Monsoon 2. ACME said the 515 (13 x 12 .080) would be equivalent to the CVP 13 x 13 and that the 525 would pick up 100 - 150 RPM. He figured the lower cup 653 would gain about 250 RPM, getting us close to 5000 on the upper end.

They said the choice is about a toss-up in that the 525 would hold (for wakeboarding and skiing) slightly better due to the higher cup but the 653 would hold well due to running higher RPMs (more solidly in the power band).

He thought the 653 might be better at altitude because of the extra RPMs. Any thoughts? Or are we splitting hairs at this point?

Thanks,

Mike

[WakeGirl]

I came from a 13x12.625 Acme to the 525 & we went from about 47-4800 rpms @ WOT to occasionally seeing 5400 on the tach at our elevation. If you have time to try our prop when we're not using it, you're welcome to. Did Madras have anything that you could try?

[CarveItUp]

I didn't get a chance to call today but will do so tomorrow. Thanks for the offer on the 525. At this point I have a feeling that I won't go too far wrong with either prop.

Am I remembering correctly that you have the Hammerhead power plant?

[WakeGirl]

Yep, but IIRC the rev limiter is at about the same point on the Monsoon, 5200 (lol, apparently mine doesn't kick in ).

[CarveItUp]

Yep, but IIRC the rev limiter is at about the same point on the Monsoon, 5200 (lol, apparently mine doesn't kick in  ).

<{POST_SNAPBACK}>

I think Joe bypassed it

[WakeGirl]

LOL, if it had kicked in he would have found a way, believe me. It's pretty common from what I've read, pretty much a crap shoot as to whether or not it will kick in.

[CarveItUp]

BTW, you're gonna need that low-pitch prop to push all that ballast! Man, I couldn't believe the wake it was putting out the other day...

[WakeGirl]

It was something wasn't it? It was the first time since we took our maiden runs behind the boat that I was actually intimidated going into the wake. Between the ballast & the people, we must have had well over 1500 lbs. Ken was just flyin' that day.

With the prop, my biggest concern is down at Shasta, Oroville & the other low lakes that we visit, how much higher we'll be revving with the thicker air down there. We're already pushing it at 5400. For $45 to re-cup the stock prop & make it perform like the 12" 515, that might be the way to go. Need to do some testing first though.

[doughickey]

Have you contacted them to see if you can have one modified?  I've seen talk of that in the past.

EDIT:  I just got off the phone with Bill Weeks at Acme & they can either re-pitch or take a little cup out of the prop.  He said that the re-pitch he really doesn't like to do on a prop that hasn't been damaged because it will never be the same as it was.  But taking some cup out will allow it to spin/slip a little more allowing the engine to rev a bit more at the bottom, getting into its power band sooner.  He said that taking some cup out wouldn't adversely affect the prop nearly as much as re-pitching.  He quoted $150 for re-pitching, $45 for taking some cup out (going from .80 cup to .50 cup, on my stock 449 13x12.625, it would efectively make it perform like a 13x12).  I'm running an Acme 525 (13x11.5) at medium to high elevation, & I'm concerned that dropping to near sea level will have me way over-revving with the 525.  So I'm thinking about having the 449 re-worked.

Just something else to think about.

<{POST_SNAPBACK}>

Tracie, been thinking about your prop re-cupping. (I've spoken to Bill in the past. Man, what a wealth of information.)

Although it's only $45 to recup a prop, you still have to pay for shipping twice. Bill says he doesn't really like to mess with a prop (CNC) because it will never be the same. Why not just buy another prop... a 13" X 12". Sure it's $300 and change.... but it's perfectly balanced, and you have "another" spare. Actually ends up being only about $200 more than a re-cup.... but you have the extra prop.

Or.... sell the 449 prop, and buy the new perfectly balanced 13 X 12. Assuming you get $150 (rough numbers) for the 449, and save $45 plus shipping for the rework..... you end up with the new prop for less than $100. Balanced.

Fun to collect props anyways.

[Sunsetter95]

Good conversation piece around your bar when the friends come over to throw a steak on the barbie. Tests your story creativity.

[WakeGirl]

Have you contacted them to see if you can have one modified?  I've seen talk of that in the past.

EDIT:  I just got off the phone with Bill Weeks at Acme & they can either re-pitch or take a little cup out of the prop.  He said that the re-pitch he really doesn't like to do on a prop that hasn't been damaged because it will never be the same as it was.  But taking some cup out will allow it to spin/slip a little more allowing the engine to rev a bit more at the bottom, getting into its power band sooner.  He said that taking some cup out wouldn't adversely affect the prop nearly as much as re-pitching.  He quoted $150 for re-pitching, $45 for taking some cup out (going from .80 cup to .50 cup, on my stock 449 13x12.625, it would efectively make it perform like a 13x12).  I'm running an Acme 525 (13x11.5) at medium to high elevation, & I'm concerned that dropping to near sea level will have me way over-revving with the 525.  So I'm thinking about having the 449 re-worked.

Just something else to think about.

Tracie, been thinking about your prop re-cupping. (I've spoken to Bill in the past. Man, what a wealth of information.)

Although it's only $45 to recup a prop, you still have to pay for shipping twice. Bill says he doesn't really like to mess with a prop (CNC) because it will never be the same. Why not just buy another prop... a 13" X 12". Sure it's $300 and change.... but it's perfectly balanced, and you have "another" spare. Actually ends up being only about $200 more than a re-cup.... but you have the extra prop.

Or.... sell the 449 prop, and buy the new perfectly balanced 13 X 12. Assuming you get $150 (rough numbers) for the 449, and save $45 plus shipping for the rework..... you end up with the new prop for less than $100. Balanced.

Fun to collect props anyways.

Exactly the process that my mind has been going through - weighing the costs of a new prop vs. re-cupping the old one. The thing that tempts me (other than cost) to re-cup is that Bill said that taking cup out of a good prop isn't nearly as detrimental to it as re-pitching. I still need to do a bunch of testing when we're at Oroville - who knows, at that level it may be perfect just the way it is. We'll just see.