Wide Open Throttle (WOT) only hits 2750 rpm (& prop advice)

[ncarroll]

Hi!

Have had a 2001 Epic S22 for about 4 years, used mostly for wakeboarding and skiing, and recently dinged the 4-bladed prop (sorry- can't remember the exact details about diameter and pitch, but I think it was an OJ Stainless 13x13) we had on it.  Our dealer is sending the prop to see if it can be repaired, and in the meantime we have a 3-blade Acme 515 13x12 LH 1.125" Nibral.

1) The question is this...Why does our boat only get to 2750rpm at wide open throttle?

The lake that we boat on is 1400 feet above sea level.  As I recall, with our old 4-blade prop, our top speed was about 40ish mph and the engine was definitely spinning under 3000 rpm (the digital and analog tach match).  With our loaner 3-blade Acme 515, I took the GPS out and got 40.6mph at WOT with 2750rpm.

The 515 also has a weird issue where it makes a high-pitched harmonic noise/chord starting at 400rpm in forward low-speed operation, and the pitch changes higher at about 580rpm, and disappears above 600rpm.  It's annoying and we can't live with it, even though the dealer said that there were no problems with correct installation. (But since we're going to return this prop, hopefully it isn't/won't be an issue with whatever we go with.)

While reading all of the previous posts on props, I see that many other people are hitting 5000-5500 rpm at WOT, and I'm wondering if that should be achievable, or if ours is so much lower because of the elevation of our lake.

If we have to buy a new prop, I will probably contact ACME with all of the details to find out which prop they suggest, but I have a feeling they will question why we have such a low WOT rpm, when redline is 6000.  The most important factor for us is quick acceleration/hole-shot to pull heavy slalom skiers out of the water, nice wake for wakeboarding, and steady-holding speed. Any ideas or suggestions?

-Nate

[lesman01]

I have an acme 525 13x11.5 and it's better out of the hole than the stock prop.

Prop should not make noise. Sounds like it may be bent. Does it vibrate?

Also, your tach must be wrong. No way you can get 40 mph with a 515 at 2720. Maybe exactly double that.

[wakejunky]

Your lake elevation is not a factor. If you were above 5000 feet you might see some issues, but not at 1400.

lesman is right there is no way that boat could reach those speeds at 2750 rpm. My best guess is you may have accidentally changed the Tach PPR from "2" to "4". It's in the digital display. It will affect the digital and analog gauges. If you look in the Maintenance section under "Accuski Manual" it will show you how to switch the Tach PPR back to "2". The setting of "4" would cut your RPM in half as you have described.

Is the prop a loaner? If so its possible it wasn't properly lapped to the shaft. I doubt a boat shop would lap a prop that was a loaner.

Does it still perform the same? If so it's most likely the Tach PPR setting.

[Bitzco]

Personally, I'm jealous. You must have a Bugatti V-12 engine in that thing to get that kind of speed at that RPM. You must have a top speed of like 95 if you access those extra RPM. Just don't ever try to turn at those speeds. Good luck!

[ncarroll]

Ha ha... yeah, I am in agreement that we must have changed the accuski PRR setting accidently at some time.  I will check on that and probably get it switched.  That makes sense, and 40 mph at 2750 really doesn't make any sense at all... thanks for setting me straight!!

Also will check to see if the prop has been lapped.  It is a loaner until we find out about the OJ 4-blade, and then we'll figure out whether we need to buy a new Acme or what....

-Nate

[boneil]

Buy an ACME!  30 day guarentee... as long as you don't tear it up.  Mine new ACME arrives Thursday!!!

[ncarroll]

Just heard back from Bill at Acme, and he suggested the  Acme 653 13 L(left) 11.5 three blade nibral 1 1/8" bore .060 cup, which should bring my WOT rpm up to 5850-5950 once I switch the setting and get my Tach reading right!

[FreeLance]

I run this exact prop on my S22, got it about a month ago per the advice of repropping from the guys at the NW Epic round up.  So far so good, great hole shot and a lot easier to hold speed with weight in the boat.  The one crazy thing about this prop, on my boat at least, is I hear a high pitch hum when I first engage the boat into gear and the prop starts to spin up.  It goes away after a few seconds though.  Never had that noise with my stock prop.  My WOT is now 5750, but I have no clue as to how fast that is since my boat is always going 50MPH regardless if I am sitting still or going all out, damn speedo...  Need to do the rewire power to the dash thing with 8awg.  Good winter project.

[PSullivan3]

So it looks fast just sitting. Ha Ha

[lesman01]

The difference between the 525 and the 653 is the cup.

525 .08
653 .06

less cup=better hole shot? all else being equal. I like my 525 though.

[cyclone]

More cup = more holeshot, generally.

Lance, adding additional power wiring to the dash will not fix your speedo. The pitots are clogged, they are on the transom. Pull off the rubber hose and use a safety pin and compressed air to clean out the pitot. Then, your speedo willl work for five minutes or so. PERFECT PASS will fix the problem fer good. If you don' wanna drill on your boat, try that new GPS speed control and let us all know how it turns out:)

[PSullivan3]

Tell me about the GPS speed control

[lesman01]

I stand corrected. Pete is correct:

 "Cup added to a prop blade controls what the prop does for the boat.  Cup on the trailing edge controls stern lift and aids to some degree hole shot.  Cup on the blade tips controls bow lift and speed.  Cup is not a generic item, it has to be designed to the application and what works for boat and  motor X will not necessarily work for boat and motor Y."

from http://www.bogerprops.com/PitchandRake.html

[FreeLance]

More cup = more holeshot, generally.

Lance, adding additional power wiring to the dash will not fix your speedo. The pitots are clogged, they are on the transom. Pull off the rubber hose and use a safety pin and compressed air to clean out the pitot. Then, your speedo willl work for five minutes or so. PERFECT PASS will fix the problem fer good. If you don' wanna drill on your boat, try that new GPS speed control and let us all know how it turns out:)

Been there, done that on the Pitot tubes.  Did not correct the problem.  I did get up under the dash and mess with the big white harness that goes in the MDCC or DECC or whatever it is and when held firm the speedo was not whacky and when let go it would peg, go down, peg, go down, rinse repeat yadda, yadda, yadda.

As for the GPS speedo it has to have a throttle by wire engine which I am pretty sure ours is so I sent them an email asking if they have a version that would work with our engines and I still have not recieved a reply and that was about a month ago.  I think if they saw some more interest from other Epic owners who are chicken like me and don't want to cut a 3" hole in the bottom of their boats they may be more willing to humor us...

For more info on the GPS system:  http://www.zerogps.com/

[sailtl]

Zero Off will NOT work on our boats. They do not have a retrofit kit available for us.