Propellor for 1992 Mercury 175 on 18' Champion

[eagle181]

Hello all,

I took my boat out for the first time and noticed that it seemed to run at low RPM. The RPMs were showing 4700-4800 at the most at full throttle on plane.

The current prop is a 15 pitch Rapture stainless and I'm thinking this may be too low of a pitch. I had a friend recommend a 19 or 21 pitch for my motor/boat size.

The boat is 18'4, and I will normally run it at 3550-3600 feet elevation. On the date in question I was at 1500 feet.

Thanks for your help!

Steve

 

[Lyle29464]

Re: Propellor for 1992 Mercury 175 on 18' Champion

The higher the pitch the slower the RPM will be. I think you have some numbers wrong. A 15 pitch should be too small for your boat. You need to check the pitch. S/B some numbers on the prop. Might need to remove it to read them. Might be a part number that will help you. After you check that out post the info and some one will be along to talk about the tack, elevation,speed etc..

 

[jestor68]

Re: Propellor for 1992 Mercury 175 on 18' Champion

Well, when I run your numbers through the trusty Mercury prop selector, it says that motor should be able to spin a 21 or 22 pitch, at the elevation you mention, depending upon what prop you select.

It would seem that your motor is not living up to it's potential. A compression test is in order as well as a tune up.

The recommended full throttle rpm range is 5000-5600 rpm. Putting more prop(pitch) on it now would only serve to pull it down further.

You will need to figure out why it's not delivering the power it should before trying a different prop, because it should be able to spin that prop well past it's rpm limit.

Double check the prop diameter/pitch, as you may be reading the 15 as the diameter not the pitch.

The Rapture is designed for off shore type boats, and not usually used on a bass boat.

 

[1FASTLASER]

Re: Propellor for 1992 Mercury 175 on 18' Champion

Well, when I run your numbers through the trusty Mercury prop selector, it says that motor should be able to spin a 21 or 22 pitch, at the elevation you mention, depending upon what prop you select.

It would seem that your motor is not living up to it's potential. A compression test is in order as well as a tune up.

The recommended full throttle rpm range is 5000-5600 rpm. Putting more prop(pitch) on it now would only serve to pull it down further.

You will need to figure out why it's not delivering the power it should before trying a different prop, because it should be able to spin that prop well past it's rpm limit.

Double check the prop diameter/pitch, as you may be reading the 15 as the diameter not the pitch.

The Rapture is designed for off shore type boats, and not usually used on a bass boat.

+1...something aint right....going to need to do some investigating to give you some correct information here. I cant speak for the difference in elevation but that does come into the equation in order to get your boat upto snuff and running correctly. I would tend to think along the lines of jestor and that you have either read the prop numbers incorrectly or someone put a VERY wrong prop on your boat. The 175 doesnt have enough hp to turn a 15" DIA prop efficently. 14 1/4 to 14 1/2" dia is the norm. Pitches ranging from 21p to 26p depending on hull configuration. I have some experience witht he Champion hulls and they like 3 and 4 blade props....it depends on what the end result it that you desire.....be it the best topend or the best handling.

 

[1FASTLASER]

Re: Propellor for 1992 Mercury 175 on 18' Champion

I forgot to say this.....get the numbers off your rapture prop and post them up please.

 

[eagle181]

Re: Propellor for 1992 Mercury 175 on 18' Champion

I forgot to say this.....get the numbers off your rapture prop and post them up please.

Wow, thanks for all the quick responses.

So the prop numbers are 14.25r15. I assume the prop is a 15 pitch correct? There is a serial number and 'Michigan Wheel', name brand I guess also written on the prop.

"A 15 pitch should be too small for your boat." I agree, I think she needs a 19 to 21 maybe...

Regarding the compression test; I did this before buying the boat and all cylinders tested great at 125 according to Cabelas mechanics.

"You will need to figure out why it's not delivering the power it should before trying a different prop, because it should be able to spin that prop well past it's rpm limit."

So, A tune up was done in August but I'm thinking maybe fuel pump is going. Symptoms of this are having to pump bulb after throttling down to keep her running, also, switching from neutral with some throttle and trying to put it in gear it seems pumping bulb is only way to do so. Guess it could be a clogged line but this issue is probably for a different thread.

steve

 

[jestor68]

Re: Propellor for 1992 Mercury 175 on 18' Champion

It sounds like you have some sort of fuel deliver issue. The motor can't produce if it's not getting enough gas.

It could be a number of things. Maybe fuel pump, fuel filter. Also check the strainer on the end of the tank fuel pick up tube for clogging.

Be careful running it when you get the fuel issue sorted out; as it will rev to the moon with that 15 pitch prop!

I highly recommend you have a certified Mercury tech(at a Mercury dealer)go over it to verify all factory specs are met. They should have a dyno to test the whole power band.

 

[dan02gt]

Re: Propellor for 1992 Mercury 175 on 18' Champion

Is that a Champion bass boat? If so I agree with what everyone else has said. Something is way wrong and it very well could be fuel like jestor68 suggested. Read this article about addressing fuel issues and let us know what you find out. Performance problems? Read Here and Upgrade Fuel Supply System FIRST!