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2004 Response prop.


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Hi All,

I have a 2004 Response which has been running on LPG, which reduces bhp a bit, with a 13 x 12 prop which seemed to handle most things well. I've now put it back to petrol and seem to have found the lost power, the holeshot will pull your arms off. Skiing at 34 mph the engine feels like its racing a bit and could take a larger pitch. The next step on the ACME website is 13 x 12.65, or possibly 13 x 13. Anyone running the 13 x 13? any disadvantages?

Thanks, Mark.

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Do an experiment with a GPS speed app on your phone.  Post the RPM's at 20mph, 25mph, 30mph, 35mph, 40mph, and at wide open throttle and that will help determine what prop you need.

I run the 13x13 ACME 425 prop on my boat, but I am close to 400hp, so that would probably not be the right prop for you.  But at WOT my RPM's are 4,900 and 49mph speed.

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21 minutes ago, Chaabo said:

What engine do you have? HP? What’s the current prop (model, not size/pitch)? What‘s your RPM @ 34 mp/h?

Of course, that would help! 5.7 carb, 310 bhp. ACME 3 blade. Not to sure on RPM as I was skiing, believe around 4200.

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41 minutes ago, SkiPablo said:

the main thing you want to see if it you are close to the max RPM for your engine.  If you are then you have the correct prop.  If it hits the rev limiter then you can prop up a little.

Now its back on petrol it shoots to 5K rpm and would seem to quite happily carry on past if I was to let it.

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26 minutes ago, Michigan boarder said:

Do an experiment with a GPS speed app on your phone.  Post the RPM's at 20mph, 25mph, 30mph, 35mph, 40mph, and at wide open throttle and that will help determine what prop you need.

I run the 13x13 ACME 425 prop on my boat, but I am close to 400hp, so that would probably not be the right prop for you.  But at WOT my RPM's are 4,900 and 49mph speed.

That will have to wait until spring now as we're out of the water. WOT was only showing around 39/40 mph.

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1 hour ago, Eagleboy99 said:

What are the RPMs at 34 mph?

Around 4200 I believe (I was behind the boat), but that was the first outing on petrol and fairly brief.

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52 minutes ago, MACC said:

Around 4200 I believe (I was behind the boat), but that was the first outing on petrol and fairly brief.

Way too high, if it’s true. You should see about 3,400 - 3,600 RPMs at 34mp/h. Would explain the crazy holeshot.

Per Indmar manual the operating range at WOT for the 310hp carb engine is 4400-4800 rpm!

https://indmar.wpengine.com/wp-content/uploads/2016/05/2003-to-2005-Indmar-Operators-Manual.pdf

 

Edited by Chaabo
Info added
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@MACC - That boat was originally fitted with the Acme 515 assuming you are running close to sea level (UK) which has the engine turning close to 100 RPM : 1 mph which puts the engine in a good power band area.  You can also go to the Acme website and enter your boat data and it tells you what their prop recommendation is:   https://acmemarine.com/pages/custom-fit

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1 hour ago, MACC said:

Around 4200 I believe (I was behind the boat), but that was the first outing on petrol and fairly brief.

Yikes!  That is way higher than mine.  I'm running near 1:1 so that is 3400 RPM.  OJ Prop - 4 blade.

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Thanks for all the replies, it seems I need to revisit this, something is amiss, either my figures, tach or prop. The props going in for a refresh next week so can hopefully confirm current pitch, although stamped as 13x12 maybe it was repitched at some point in the past??

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22 minutes ago, Woodski said:

@MACC - FYI type of fuel should not change engine RPM so your old data should be valid on how fast engine is spinning.  What brand / model # is the prop on your boat?

Yes, understood. The prop is an acme 515. We picked the boat up mid season from a ski club with the boat being a bit tired, running on LPG and needing a bit of TLC. Used it as was for the rest of the season knowing it was going to be a winter project to change to petrol and do a bit of a refurb. One item on the list is the rev counter which doesn't work so we have been skiing off the speedo, it has perfect pass but my wife doesn't use the counter on this, hence my uncertainty on the RPM. It had good power but felt like there was more to come, changed to petrol and renewed rotor arm, cap, leads and plugs last weekend and the difference is incredible, its like a different boat. Now it feels like it could take a larger pitch to take bit of strain off the motor.

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I've only skied that generation RLXi with the Monsoon engine, but have skied it with ACME 13x12, 13X12.625, and 13X13.

13x12 is perfect IMHO

13x12.625 would be fine if you wanted to soften the hole shot a bit

13X13 was too tall of a prop IMHO.  The boat was very soft out of the hole, didn't feel like a firm pull when up to speed (due to lower RPM's maybe ?)

If I were you, I'd have that prop refurbished to good condition and have the driver learn that you don't need 100% throttle all the time.

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If your tachometer is reading 4,200 RPM at 55 kph / 34.2 mph and you are running that 515 prop, the tachometer is not providing good data.  I would clean all the connections and make sure they are tight and particularly check all the ground (earth) connections.

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  • 2 weeks later...

So to add to this, had a call from the prop shop today, all three blades are 'significantly' bent, and measuring around a 10 pitch which would certainly explain some of the oddities I've been seeing. He says they are bent exactly the same which seems odd but cant have been repitched this low. Repairing back to the manufactured 12 pitch, excited to try it again but this will have to wait until spring. Thanks for the input on this.

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  • 2 weeks later...

Looks like you have found at least the most significant issue with speed v. engine RPM.  Nibral is pretty soft so not that surprising the blades lost a bit of pitch, that seems pretty extreme and to add to @UWSkier comment, I do have an Acme that has lost pitch and cup but not that much (mine was ~200 rpm change).

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On 12/12/2019 at 5:09 PM, Woodski said:

Looks like you have found at least the most significant issue with speed v. engine RPM.  Nibral is pretty soft so not that surprising the blades lost a bit of pitch, that seems pretty extreme and to add to @UWSkier comment, I do have an Acme that has lost pitch and cup but not that much (mine was ~200 rpm change).

What prop have you been running, before and after the recent rebuild?  I think I recall you doing a custom pitch or something.

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@Michigan boarder - I have been running a 449 for a couple of years although with recent engine build probably will go to a 425 or will add more cup to the 449 as there is plenty of grunt with the engine config I am running.  I used to run a much modified 653 where I added quite a bit of cup which made it a pretty nice prop, got it cheap so it was a fun experiment.  Both the 653 and the 515 I ran did seem to flatten a bit over time.  My boat does not have a lot of resistance since pretty light but I do transmit a fair amount of power / torque from the shaft side.  (Note - I don't recommend anybody copying my prop selection for their application, my boat is not as delivered).

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