Prop size for old Mercury

[gpfishingdude]

I have had the chance to run the old 1986 50 hp. Mercury on the 18' Bass Buggy-wot- lately and it looks like it tops out at about 4500 rpm and 15 mph. tops. I dinged the prop that was on it shortly after we bought the boat and replaced the prop with a different sized one. Could anybody tell me what size and pitch prop would get me the best performance? That is MPGs per MPH. and with the kind of rpms it should be turning? Do I need a different prop on the pontoon boat than somebody would need on their ski boat? It would be nice to see a little better gas mileage in the end. Thanks!!

 

[MH Hawker]

Re: Prop size for old Mercury

It all depends on several things, the most important is your present RPMs and what pitch is on it. also motor height. You can adjust the max RPM by changing pitch. The rule of thumb is 200 to 300 per pitch change altho pontoon do not all ways work by this rule. To start off you have to know what your present pitch is and motor max RPMs and present RPMs and your speed on GPS is also very help full to note changes. Then by changing prop pitches you can note the performance changes.

 

[gpfishingdude]

Re: Prop size for old Mercury

Thanks Hawker! I think the max rpm should be at least 5000 for this motor and all I can get is about 4500. This is the first time we have had the boat on any big water since last fall so this is kind of like an advanced shakedown cruise. I will figure out what pitch I need to get another 5-7 hundred rpms out of it by figuring about 250 rpm per increment of pitch change.

 

[steelespike]

Re: Prop size for old Mercury

Is this a 3 cylinder or 4 cylinder? 3 cylinder is rated at 5300-5800.4 cylinder is 4800-5500.Actually a 4 cylinder would be a 1985.
Your prop size is under the prop nut. or near the base of the blades.
a test run with lightly loaded rpm and gps speed.

 

[jestor68]

Re: Prop size for old Mercury

The Tracker web site will provide the weight data for your pontoon boat.

Take that to the Mercury web site and use their prop selector to find the right prop for your 50 hp Mercury motor on a pontoon boat.

You'll see that they recommend one of their Black Max Extra Area aluminum props(for pontoon boats).

They are only available from Mercury dealers.

 

[gpfishingdude]

Re: Prop size for old Mercury

This motor is a 4 cylinder so maybe it is an 1985 model. I'm sure the book tells what the recommended RPMs is supposed to be but I didn't bring the book along on this trip. The old Bass Buggy is a 1991 model so I will have to do some digging to see what the specs were in those days. Thanks for all of the help, I will see what I can do with it now.

 

[steelespike]

Re: Prop size for old Mercury

bass Buggy is 1440 lbs came with a 40

 

[gpfishingdude]

Re: Prop size for old Mercury

I am trying to get the boat and motor in to a dealer for a tune up to make sure that the motor is performing to it's peak first. Then I will see what it costs for one of those new Mercury four blade props that are made for pontoon boats. They have a four blade prop out now that they claim will out perform the Black Max extra area for pontoons. Supposed to be better out of the hole because of the smaller diameter and better on the top end too. I haven't priced them yet though.