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Andrew63

2011 RLXI 350 Monsoon Prop

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Andrew63

Hi

Had a look but could not locate a previous post regarding the prop, speed & engine RPM.

Operating in tidal rivers brackish water so I am near enough to sea level.

I am getting 42.5 mph (zero off GPS) top speed with the engine running at 4550 rpm.

Takes about 10 seconds from WOT to wind up to this speed from about 36 mph.

The manual indicates the 350 Monsoon should operate between 4600 & 5200 RPM.

The 42.5 MPH is with 4 people on board, 2 x 200lb adults, 2 teenagers about 120lb ea & a full tank of fuel.

Prop is an acme 3 blade 525 13 x 11.5 which appears to be the standard issue for the RLXI.

Had it recently checked & balanced, one of the blades was out 6mm, previous owner may have hit a log or something.

I had expected to be either mid range RPM or a tad quicker.

The 42.5 mph is just enough to foot at, but it looks like there is nothing left in reserve & with the RPM on the low side, there appears to be no option to increase either cup or pitch of the prop.

The boat has 260 hours on it.

Q. Is this considered normal to be below the recommended operating RPM?

I guess not.

So where do I start looking?

Have ordered a set of plugs as I have had the boat for 6 months now only changed the engine oil & filter a few month back to have a starting point.

Thanks in advance for your thoughts

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wedge88

Not sure on the prop but I had a 2006 RLXI with 350 and I could hit 50mph empty and 46-47 with the load you describe. It would rev at around 5000-5100 rpms. I had the stock prop but not 100% sure what that was. I thought it was a 535. My dad has a 2012 TXi with 350 and seems to top out around 45-46. I now have a 2004 SSLXI with same engine and it tops at 48 5100rpms. Not sure I have helped but at least gives you some comparisons.

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Dare2goBare

Just to cap off to what Wedge said.

I have the Acme 515 prop pushed by the L96. Full boat with full tank of gas I get

between 47 -48 Mph at sea level. @ 5000-5100 RPM. Lots of tourq.

With your 350 thinking re-proping my be what to look at. Give Acme a call

with your specs, they will be glad to help. I've talked with them in the past very helpfull.

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Woodski

I would also suggest along with a chat to Acme on optimum prop, that you check the running gear. Verify the prop shaft turns freely, the shaft is not bent & the rudder bearing clearance is okay. Also, an engine to shaft alignment check would be a good thing to do. You should see at least the upper 40's for speed IMO and close to 5000 rpm WOT.

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Andrew63

I would also suggest along with a chat to Acme on optimum prop, that you check the running gear. Verify the prop shaft turns freely, the shaft is not bent & the rudder bearing clearance is okay. Also, an engine to shaft alignment check would be a good thing to do. You should see at least the upper 40's for speed IMO and close to 5000 rpm WOT.

My thoughts are the RPM is down & hoping for some points the check.

Checked the prop shaft and is is within 0.003" at the prop nut & 0.005" mid way between the cutlass bearing & hull.

Checked the shaft alignment a few months back & could not fit 0.003" in anywhere around the coupling with the coupling nuts just holding the faces together.

Prop shaft spins with one hand, a bit of resistance when the cutlass bearing is dry, loosens up when wet.

Rudder bearing clearance??? Grabbed hold of the rudder and there is no movement, apart from how is is supposed to turn.

Part of the reason for checking all this is I am considering the FAE to cut the exhaust noise down, currently running the silent tip exhaust tips.

Should I be looking for fuel filters or anything along these lines, being the pressurised fuel system, I have been reluctant to just pull things apart. I believe the fuel filter is in the fuel tank, not sure though.

Edited by Andrew63

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eyekode

If you end up doing the FAE thing let me know as I would be interested in your old exhaust. But I have heard FAE drops a couple MPH off the top end.

I guess if your WOT RPM is low then your motor is not putting out enough torque for your prop, shaft, alignment etc. The prop is not that aggressive, the alignment sounds good. Do you feel much vibration when running or is it smooth?

How about air intake and exhaust? Could there be some restriction there?

Good luck!

Edited by eyekode

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Andrew63

If you end up doing the FAE thing let me know as I would be interested in your old exhaust. But I have heard FAE drops a couple MPH off the top end. I guess if your WOT RPM is low then your motor is not putting out enough torque for your prop, shaft, alignment etc. The prop is not that aggressive, the alignment sounds good. Do you feel much vibration when running or is it smooth? How about air intake and exhaust? Could there be some restriction there? Good luck!

The reason I started checking the alignment & prop balancing a few months back is I have a slight vibration when running at 30 mph & above.

Had the prop checked using propscan & found one of the blades was out nearly 1/4". The prop had signs of a previous repair.

had the prop repaired to bring the blades back into alignment for the 11-1/2" pitch & balanced.

Started to get excited thinking I had found the vibration problem...not the case.

Went out in a 2012 RLXI & found the same vibration. Put it down to maybe I am being too fussy.

As to Air intake or exhaust restrictions, air is not subject to any dust & looks clean, exhaust, not sure how to check without pulling it apart.

Leaning towards, may have to take it into the shop & hope they can find the problem & not just charge me to find nothing.

It is as if it has been governed down or starving for fuel.

Will wait till the new plugs arrive, try them & if no improvement, book it in to the shop. Worst part is the shop will charge me the cost (or close to it) for the FAE. may put back the FAE for a few months.

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