Am i running the right prop??

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mtduckhunter

Petty Officer 1st Class
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I have a 1984 ranger 372v with a mercury 150 black max with a 23p lazer II prop. My max speed is 53.8 MPH on GPS, With the motor trimed up with a good rooster tail, but i am running about 6000 RPM and i think i even seen the needle bouncing a few times. The boat has a jackplate with about 4 inches of setback.

Should i go up to a 24p to bring the RPMs down?

I would also like it a bit faster.
 

hwsiii

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Re: Am i running the right prop??

I know you don't know duckhunter, but we need more information.
Boat weight, WOT RPM range recommended for motor and lower gear ratio of motor. Then we can crunch some numbers for you.

H
 

mtduckhunter

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Re: Am i running the right prop??

Well lets see, . . I think i read somewhere that the boat weighs 1200 lbs, the WOT RPM max is 5600, and i think the gear ratio is 1.87, someone correct me if im wrong, it a 1984 Mercury 150 hp black max, its new to me but this is what i have reserched.

And it is a 17', 6" boat, 7', 4" beam if that helps any.
 

11rufus11

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Re: Am i running the right prop??

Are you noticing any excessive slippage?
 

hwsiii

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Re: Am i running the right prop??

duckhunter your slip is exceedingly high at 23%.
mtduckhunteriboats.jpg

Usually that means not enough diameter in the prop,

H
 

mtduckhunter

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Re: Am i running the right prop??

I dont know if this means anything, . . but when i run WOT trimmed up to where it should be, and the RPMs are up to at leat 6000 (thats as high as the tach reads) Shortly after it start bogging like its running out of gas, i back off the throttle and its fine.

I will try to find the diameter and let you guys know.
 

mtduckhunter

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Re: Am i running the right prop??

I checked the diameter and it is 13 1/2"
 

11rufus11

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Re: Am i running the right prop??

A 14 5/8 diameter with a 23 pitch prop would probably work for your boat, or a good starting point anyway. I believe Quicksilver Torrent or Tempest has that diameter if you want to stick with a Merc product. Expensive though.
 

hwsiii

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Re: Am i running the right prop??

Duckhunter, the first thing you need to do is check the tachometer, after you know it is correct, these are my recommendations. Change to a Laser II 13 3/4" x 25", these are numbers for that particular prop using my formulas. You will be turning right at 5,400 RPM.

mtnduckhunteriboats.jpg


I hope this helps you.

H
 

mtduckhunter

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Re: Am i running the right prop??

I believe Quicksilver Torrent or Tempest has that diameter if you want to stick with a Merc product.

I was looking at the Torrent and i called a prop shop and he recommended the Tempest.

Thanks hwsiii, great info!!! i am assuming the tach is correct because the motor is idling at about 800 RPM.

Also i have noticed that the motor is mounted 5 1/2" above the very bottom of the boat, is this a little high?
 

hwsiii

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Re: Am i running the right prop??

I certainly hope you have a water pressure gauge on it. You need to know you have enough water pressure in the engine so it won't overheat, other than that it is fine.

H
 

mtduckhunter

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Re: Am i running the right prop??

No i dont have a water pressure gauge, i would like to replace my trim gauge with one.

Is there a way that i could trade my laser prop for a laser 25p like you recommended?
 

hwsiii

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Re: Am i running the right prop??

You can try calling some dealers and see if they will let you trade up.

H
 

mtduckhunter

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Re: Am i running the right prop??

I called a guy today that deals with props only and i asked him about trading and he said he didnt want a Laser!

I will try calling a few Mercury dealer.
 

hwsiii

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Re: Am i running the right prop??

I wish you luck duckhunter.

H
 

mtduckhunter

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Re: Am i running the right prop??

I lowered the motor 1 1/4", made a test run and went 57.3 (GPS) and was still climbing when it started chinewalking and i was between 5600 and 5800 RPMs.
 

junior1113

Senior Chief Petty Officer
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Re: Am i running the right prop??

lot better id still look into a 24-25p good luck
 

mtduckhunter

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Re: Am i running the right prop??

Yea im very pleased!!

But i still wana go faster, so yea i think i will eventually get a 24 pitch, the tempest is the one i really want to try, not really worried about holeshot because it gets up great now, but at $500!! It will have to wait a while.
 
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