Max RPM advise

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DWRAT
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Location: Phx,AZ

Max RPM advise

#1 Post by DWRAT » Sun Apr 30, 2017 1:58 pm

My brand new Mercury 150 4 stroke with a 15X15 Enertia prop is getting 5,300-5,350 max RPM.
It has a great hole shot, mid range power & hitting 40 mph.
Any reason running 5,300 rpm could be problem?
Just trying to save buying a 15.3X14 prop for another $500.00
I know the range is 5,000-5,800 and I have always heard to try to be at the top of the range, but why?
Thanks
Dan
2012 SouthBay 722CRO 115hp Merc 4-stroke. Edit, make that a 150hp Merc 4-stroke now.

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Rick McC.
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Location: Weeki Wachee, Fl

Re: Max RPM advise

#2 Post by Rick McC. » Sun Apr 30, 2017 3:22 pm

[quote="DWRAT"]My brand new Mercury 150 4 stroke with a 15X15 Enertia prop is getting 5,300-5,350 max RPM.
It has a great hole shot, mid range power & hitting 40 mph.
Any reason running 5,300 rpm could be problem?
Just trying to save buying a 15.3X14 prop for another $500.00
I know the range is 5,000-5,800 and I have always heard to try to be at the top of the range, but why?
Thanks
Dan[/quote]

I'd be happy with what you have now.
Rick

Sights are for the unenlightened.

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mpilot
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Location: Lake Murray, SC

Re: Max RPM advise

#3 Post by mpilot » Sun Apr 30, 2017 3:45 pm

[quote="DWRAT"]My brand new Mercury 150 4 stroke with a 15X15 Enertia prop is getting 5,300-5,350 max RPM.
It has a great hole shot, mid range power & hitting 40 mph.
Any reason running 5,300 rpm could be problem?
Just trying to save buying a 15.3X14 prop for another $500.00
I know the range is 5,000-5,800 and I have always heard to try to be at the top of the range, but why?
Thanks
Dan[/quote]

That 15x15 is what all of the Brunswick brands ship with. You'll pick up a little rpm with the drop in pitch but you'll lose some back with the diameter and no real speed gains. I'd stick with what toy have.

Bamaman
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Re: Max RPM advise

#4 Post by Bamaman » Mon May 01, 2017 12:28 pm

40 mph is the max you should expect out of that engine and boat.

You're good to go. The 150 FourStroke I think is a 5800 rpm max motor anyway. Close enough.
'12 Bennington 24' SSLX Yamaha 150

r&s20
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Re: Max RPM advise

#5 Post by r&s20 » Mon May 01, 2017 5:54 pm

The reason to try to get to the top of RPM range, is so when you load boat heavier than normal (or pulling tubes) you will still be within the WOT RPM range. maybe lower rpm's but still range.
If you are hitting 5300 with normal load i would run what you have
if it ain't broke-it ain't ours
94 smokercraft 20ft 90hp johnson
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Ozark Bob
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Location: Lake of the Ozarks Climax Springs, MO

Re: Max RPM advise

#6 Post by Ozark Bob » Mon May 01, 2017 6:13 pm

I have the same engine on my South Bay 522RS turning a 15.3 X 14 Q3 prop, same as the Enertia. The best I can get at WOT is 5400 rpm. I was also concerned about not getting into the upper rpm range so I contacted Mercury for their opinion. They said "Your rpms are exactly where we recommend. This should cause no issues with your engine. Issues can arise when the wot rpms are much lower ie. 4000 rpms."
2014 South Bay 522RS
Mercury 150 Four Stroke

DWRAT
Posts: 142
Joined: Sat Jun 16, 2012 9:17 pm
Location: Phx,AZ

Re: Max RPM advise

#7 Post by DWRAT » Mon May 01, 2017 11:10 pm

[quote="Ozark Bob"]I have the same engine on my South Bay 522RS turning a 15.3 X 14 Q3 prop, same as the Enertia. The best I can get at WOT is 5400 rpm. I was also concerned about not getting into the upper rpm range so I contacted Mercury for their opinion. They said "Your rpms are exactly where we recommend. This should cause no issues with your engine. Issues can arise when the wot rpms are much lower ie. 4000 rpms."[/quote]

Bob,
What top speed are you running?
2012 SouthBay 722CRO 115hp Merc 4-stroke. Edit, make that a 150hp Merc 4-stroke now.

DWRAT
Posts: 142
Joined: Sat Jun 16, 2012 9:17 pm
Location: Phx,AZ

Re: Max RPM advise

#8 Post by DWRAT » Mon May 01, 2017 11:11 pm

Thanks everyone for your replies.

Dan
2012 SouthBay 722CRO 115hp Merc 4-stroke. Edit, make that a 150hp Merc 4-stroke now.

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Ozark Bob
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Location: Lake of the Ozarks Climax Springs, MO

Re: Max RPM advise

#9 Post by Ozark Bob » Tue May 02, 2017 5:13 am

I get 35 mph at 5400 rpm with just my wife and I on board and about half fuel. When I bought the boat it had a 15.25 X 14 PowerTech prop and I could only get 32 mph and 5300 rpm. I got a pretty good improvement with the Q3 prop but I am still searching for a few more rpms. I am going to try raising my engine 1 hole to hole #3 and see what happens. Not sure I will see any gains but it's worth a try.

Your numbers sound really good. Do you have the full center tube? Mine is the 3/4. You could pick up a couple hundred rpms if you went to a 14" prop but I don't think you would gain any speed. I looked at your numbers on the BAM Prop Slip Calculator and with you 15" prop turning 5350 rpms it showed a Theoretical Speed of 40 mph. Assuming a 200 rpm gain with the 14" prop it showed a Theoretical speed of 41 at 5550 rpms. Both those numbers indicate 0% slip which is pretty much impossible. How are you measuring your speed? Boat speedo or GPS?

http://www.go-fast.com/Prop_Slip_Calculator.htm

If you do decide to try the 14" prop and like it you wouldn't have any problem selling the 15 X 15 Enertia.

Bob
2014 South Bay 522RS
Mercury 150 Four Stroke

DWRAT
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Re: Max RPM advise

#10 Post by DWRAT » Tue May 02, 2017 6:03 pm

GPS speedo, 3/4 toon, full under skin, motor one hole down from the top hole, 2 people and a dog with full camping gear running in the Colorado river but in a wide section. (see picture)
Maybe the flow helps outs a bit but from many past testing, only 1 mph in the narrow section.
GPS reading in the center bottom of crappy picture.

http://i1129.photobucket.com/albums/m51 ... G_2047.jpg
Last edited by DWRAT on Tue May 02, 2017 7:40 pm, edited 1 time in total.
2012 SouthBay 722CRO 115hp Merc 4-stroke. Edit, make that a 150hp Merc 4-stroke now.

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Ozark Bob
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Re: Max RPM advise

#11 Post by Ozark Bob » Tue May 02, 2017 6:57 pm

Those are great numbers. Wish mine would go that fast. I think we have very similar boats. Mine also has the 3/4 center tube with full under skinning. Overall length 23'9". Makes me wonder why I can't get a couple of more MPHs. I think if I had your boat I would leave just as it is and enjoy!

Bob
2014 South Bay 522RS
Mercury 150 Four Stroke

Scott1
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Re: Max RPM advise

#12 Post by Scott1 » Sun May 07, 2017 2:35 am

If you are comparing boats and speed you need to know how each motor is mounted. If mounted too low in the water you will not get the top speed.
2014 Bennington 2375 RCW with Verado 250 Pro and Simon Motorsports ECM upgrade to 325 HP
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