Can't get pass 4400 rpms on my Mercury 60 4-stroke

9/10/18 @ 8:33 AM
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djrunner
djrunner
USER since 9/10/18

Purchased a used 2017 Lowe Stinger 17' aluminum boat with a 2016 Mercury 60 4-Stroke (full factory warranty still remaining).  After several weeks of not  driving the boat, over the Labor Day weekend I had several days to consecutively run it.  It was topping out at 20 mph and not going over 4000 rpm.  The longer I drove the boat the slower it was getting.  At one point, it was maxed out at 15 mph.  Took it to my local Mercury dealer (not where I bought it).  They called me and said they found trash in the thermostat and the motor was in Guardian mode.   They cleaned it out and reset the code.  Took the boat back out this weekend and it still didn't get but about 24 mph running at 4400 rpm.  Called the dealership back and they said they wound have to do diagnostics out on the water instead of the shop.  This motor has 32.5 hours on it.  Is this all the power that I can expect out of it, or could something else be going on?  It idles smooth and does not bog down.  It just has no more power once it planes off.  EDITED - after suggestions, I pulled the information on the prop.  Also called the dealer that installed that prop.  It is 10.25 diameter and 14 pitch prop.  Every scenario I run through Mercury's website doesn't recommend a 14 pitch prop.

Edited on 9/10/18 12:21 PM
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9/26/18 @ 8:40 AM
djrunner
djrunner
USER since 9/10/18

Tuffy2, Speed is reading from gps. Running mostly on smooth water, with maybe a little chop. When I swapped props, I only eyeballed the anti-cavatation plate in relation to the hull. I should have measured. Just eye-balling it though it is even with the bottom of the hull, so it likely needs to be raised. As for the hydrofoil, would that help with porpoising? I definitely realize that I don’t have a speed demon, but was hoping to get close to what the Lowe website posted specs on this model. Thanks again for all your input.

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9/20/18 @ 11:11 AM
Tuffy2
Tuffy2
MEMBER since 7/7/04

Is your speed reading from your gps or a speedometer? Both can actually be inaccurate, but the gps is closer. Were you running on flat water, or some chop?

If you are turning that prop at 6000 rpm’s then you wouldn’t want to raise your engine, as that will increase your rpm’s. You also would not get any benefit from a hydrofoil.

As far as engine height, your anti-cavatation plate should be about 1” below the planing surface of the hull. If it is lower than that, you could raise your engine one hole and exchange your prop for the 13 pitch, but you will lose hole shot.

Your boat is never going to be a speed demon, so I would think that your goal should be hole shot and staying on plane.

I would never run a full tank of gas, or fill both livewells.

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9/20/18 @ 10:17 AM
HotPockeT
HotPockeT
USER since 3/18/11

Check out Lowe website. They have test results for 60 and 75hp Merc four stroke for this exact boat. 

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9/20/18 @ 8:28 AM
djrunner
djrunner
USER since 9/10/18

UPDATE on Prop switch. 

Original setup -  2017 Stinger 175 w Merc 60 HP 4S.  Propped with a Stainless Steel 3 blade 10.25x14" PowerTech.  Calculated Max Weight - Dry Hull-1178,People-650,Fuel-132, 2 live wells@192each, motor-247 = 2600 lbs total max.  Typical run weight approx 2400 lbs.  Boat never exceeded 4500 rpm and ran top speed 24 mph.

New prop - Mercury SpitFire 10.6x12" aluminum 4 blade.  Ran boat after swap yesterday with approx weight 1650lbs (2 people,no water in live wells, 1/2 tank gas).  Noticeable difference in hole shot and getting on plane.  WOT is 6000rpm which is the target.  Top speed is 27 mph.

Motor is mounted in 2nd hole down.

Any more suggestions that might increase top speed?  I was expecting to be able to run at least 30 mph in this boat.  Would moving the motor up to the top bolt hole, or adding a hydrofoil help with speed?

Thanks everyone for all your advice thus far!!

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9/11/18 @ 10:50 AM
Tuffy2
Tuffy2
MEMBER since 7/7/04

A four bladed prop has more prop surface than a three blade, so it will hold the boat up on plane easier. It will get the boat up on plane faster, plus it will hold the boat up on plane at slower speeds. You will lose about 2mph compared to a three blade, but the trade-off will be worth it.

By raising the motor up one hole, or 1”, this will increase your rpm’s giving you more speed. I would have your dealer look at your boat to be sure this wouldn’t be too high. If your motor is too high, it won’t get enough water intake for cooling.

There is a video on the internet that shows them testing a Mercury Spitfire prop on a boat with three people onboard. The boat has a Mercury 60hp four stroke motor on it.

I sent you a message.

Edited on 9/11/18 10:59 AM
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9/11/18 @ 10:02 AM
djrunner
djrunner
USER since 9/10/18

Thanks Tuffy for your lastest input. This is my first boat, so pardon any ignorant question that I may ask. Just trying to learn.   If I go with a 10.25x12 per your suggestion, do I look for a 3 blade or 4 blade prop?  Can you explain the difference in performance?  I'm sure raising the motor an 1" will be necessary, but I haven't checked that part yet.  This very issue is probably why the original owner of the boat traded it.  I was looking for a used boat with a warranty and thought I found the perfect boat.  Just hasn't performed as well as I had hoped.

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9/11/18 @ 7:52 AM
Tuffy2
Tuffy2
MEMBER since 7/7/04

The boat in question here is 17’, 85” wide, and 1,000#. The boat is rated for 80hp, so it is my opinion that the boat is underpowered. The 10.25 x 12 prop will increase the rpm,s and raising the motor 1” on the transom will lift the rear of the boat while on plane, thus also help decrease the drag, while helping to increase the rpm’s.

Prior to 2005 this motor was actually a Yamaha. In 2005 it was built in Mercury’s new plant in China. So the older models are not comparing apples to apples.

Edited on 9/11/18 7:55 AM
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9/11/18 @ 7:00 AM
Hunter&Hound
Hunter&Hound
USER since 7/24/01

I have  2001 version, and run a 3 blade stainless 13".  I can push it over 6000 rpm and hit 31-32 mph with a light load.

A 4 blade 14" seems like too much.  I'd agree that 12" would be better if 4 blade is what you want.


Good luck!

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9/10/18 @ 6:46 PM
djrunner
djrunner
USER since 9/10/18

Thanks everyone for your tips on the prop.  Service tech was able to come out this afternoon and run the boat hooked up to the computer.  With 3 people in the boat the boat never ran over 22 mph.  Diagnostically the motor is great, but he too thought it is a prop pitch problem. I really appreciate the information you dug up Tuffy2!!  I will wait to see what the dealer recommends tomorrow.

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9/10/18 @ 2:25 PM
westfieldW
westfieldW
USER since 10/9/16

I have a 2003 60 horse four stroke I know it's older than yours but I think they're pretty much the same. this is the part number on a stock prop that came with my boat. Black Max (10 1/2 x 13") MERCURY RH Propeller, 48-816704A45

The boat will usually run about 5,500 RPMs at full speed with that prop. I switch to a 4 blade prop 8M8027511 because I was not getting enough torque to put the boat on plane with three guys. The 4 blade prop runs a little under 6,000 RPM at Full Throttle. Which is the Max RPM for that motor.

Edited on 9/10/18 2:27 PM
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