1975 85HP Johnson ?

[joeyd50]

I have a 1986 Skeeter Starfire 175 bass boat 18.5 feet with a 1975 85HP Johnson, my top speed is 32.6 MPH according to my GPS, the motor is running at 5500 RPM with a 13X19 aluminum prop, I'm looking at a 3 props on E-Bay, one is 13.5 X 19 Stainless make unknown, a 13 X19 Solas stainless and a Johnson 14 X 19 aluminum . I know the 13X19 will fit, I'm wondering if the 13.5 and the 14 will fit my motor. I'd appreciate any help here.
Thanks
Joe

 

[HighTrim]

Re: 1975 85HP Johnson ?

Why are you switching? You are in the WOT RPM range for your motor, depending on the load when tested. Current prop damaged? More speed? Various boating activities? If you had a light load when tested, you may want to lower the pitch by an inch or two, bringing your WOT RPM to 5700 or 5900.

 

[Dhadley]

Re: 1975 85HP Johnson ?

This will probably get moved to the prop forum so watch closely.....

Anyway, we'll assume you're looking for more speed. A typical Skeeter needs all the bow lift it can get from the prop & set up. A typical aluminum prop doesn't have much rake so you're probably not getting a lot of help there.

Some ss props have more lift than others. A Raker has more lift than an SST. A Turbo Lightning Jr (if you can find one) has more yet.

Another thing that helps get bow lift is a jackplate (because of the setback). You didn't mention if you had one or not.

A prop for your V4 will have 13 solines. A V6 prop will have 15. If a given prop has 13, it'll fit. The 13" & 13 1/2" diameter very likely will have 13 splines. On the 14" diameter you may want to check it out first.

Find out all you can on the 13 1/2" prop. Rakers and Lightning Jr's are 13 1/2" diameter. However, Rakers & Jr's are in even number pitches. Let us know what you find out.

 

[Dhadley]

Re: 1975 85HP Johnson ?

And just in case anyone - ANYONE - is wondering, I do not have any Lightning Jr's to sell. Don't read anything into this.

The proceeding post was not a solicitation to sell nor an invitation to buy.

 

[joeyd50]

Re: 1975 85HP Johnson ?

I was just going to do some experimenting, I was hoping for more speed, I have no Jackplate or power tilt & trim, all the props are 13 spline, I know the WOT at 5500 RPM's is were it should be. I appreciate the help, but do you guys think I'm just wasting time and money? I'm really not complaining about the 32.6 MPH I just figured it don't hurt to ask.
Thanks Again
Joe

 

[Dhadley]

Re: 1975 85HP Johnson ?

We're all always looking for a little more. Obviously power trim would help too. You might look at the CMC (Cook Manufacturing Co.) trim. It bolts on like a jackplate and has about 4 or 5" of setback if I remember correctly. Instead of moving up & down it moves in & out. Might help kill 2 birds....etc.

You might look around for a newer motor with more displacement and trim. Ya never know what's available. Especially if you like the boat and plan on keeping it. Can't hurt to upgrade the motor.

 

[walleyehed]

Re: 1975 85HP Johnson ?

I'd follow Dhadley's suggestion on the upgrade...maybe something like a '94-up V4 looper...say a 115hp, set-up for 5800-6000. That boat would likely handle a 150 as well.

 

[joeyd50]

Re: 1975 85HP Johnson ?

Yea, I know its underpowered, I won the boat on E-Bay for $860.00, I live in NJ and the boat was in Tampa FL., I gave my son $300.00 for gas and tolls to pick it up. A few years later I won the motor on E-Bay for $300.00, besides putting new carpet and cleaning it up, this is all I have invested in this boat, now the boat looks and runs great, I'm just not getting to the hot spots first, but I'm getting there. If this motor was to take a crap I would definitely go up in HP.
Joe

 

[steelespike]

Re: 1975 85HP Johnson ?

You might try fine tuning your setup.Raise the motor til just before venting becomes a problem.Play with the trim.If one notch seem not enough and the next seems too much buy or make some wedges so you can get 1/2 a notch.
Once you have it all set you can upgrade the prop usually going to stainless
same size will lower rpm because of better bite.Usually you drop in pitch when going to stainless.Usually aq prop shop will let you test for just the right prop if you are buying.New prop might give you a little more height with less venting.

 

[joeyd50]

Re: 1975 85HP Johnson ?

Ok, I think this will be my last question about these props. All these props have the same pitch 19, but what do you think changing the diameter would do?
Thanks
Joe

 

[Dhadley]

Re: 1975 85HP Johnson ?

Not all props are created equal. Not all 3 blade 19" pich props are created equal. You also have to figure in cupped or not, how much cup, cup placement, rake angle, blade design, blade shape etc. Is the pitch straight or progressive. How progressive, and where a given prop is measured.

Generally speaking, more diameter should let you run the motor higher which means less drag. More diameter also means more blade area. That can be good or bad depending on the hull design, set up & intended use.

 

[joeyd50]

Re: 1975 85HP Johnson ?

Thanks for all the info guys, I'm going to leave thing just as they are.
Thanks Again
Joe