2005 mercury 60 hp bigfoot

just purchased suntracker 22 party barge with 60 hp 4 stroke big foot motor and at wot it is only turning 3500 rpm but the manual says max rpm is 5500 to 6000 rpm,should there be any concern with the low rpm.

Assuming the motor is tuned properly and has no mechanical issues, it sounds like you have way too much prop.

You have a huge mobile "dock" that you are trying to push with a motor that is better suited to a 15 foot aluminum boat.

Yes, the "bigfoot" part helps with it's lower gears, but the prop still needs to be matched for what you are asking it to push.

If an outboard is "unable" to reach it's max rpm range it is "overloaded". That can lead to a pretty short life for the motor, so definately something you need to address - and quickly.

As a first step I would give the motor a good go over - tune it up, run new gas, decarb the engine (or have a shop do it if you don't mind opening your wallet for another few hundred bucks).

Buying a used 4 stroke is always a gamble - even if it's only a couple years old. They are way more picky about proper maintenance than older 2 strokes.

If it is mechanically sound and the only issue is prop pitch, given that you are falling over 2000 rpms lower than where you should be, I'm not even certain that you could go with a low enough pitch for it to ever work properly - you may have way too small of a motor for what you are asking it to push.

But first things first - tune it up and see what kind of rpms it can turn..

what do you mean when you say it way have to big of a prop on it?

Ok, think of the prop as an extension of the gears.

A bigfoot already has "low gears" compared to a (regular) outboard, but they are "fixed" at 2.3:1 (a regular 60 would be about 1.8:1).

Since that particular motor could be used on a variety of boats, the second half of the equasion is the propeller diameter and pitch.

If that motor is pushing a relatively light vessel that has good hydrodynamics it would probably have a 13 or 14" diameter, 13 or 15 pitch propeller.

The more weight the motor is asked to push, the harder it has to work. If it's working too hard (rpms not getting into the prescribed range) you have to lower the pitch (and possibly the diameter) in order to lessen the load on the motor.

Basic rule of thumb - for each 1" decrease in pitch, your rpms will rise about 200 and each 1/2" decrease in diameter will also raise your rpms by about 200.

So if you are topping out at 3500 rpms, and you should be (at minimum) in the 5500 range that MAY mean that your prop is about 10" of pitch more than that motor can effectively turn given how much weight you are asking it to push.

If your current prop is a 14D (diameter), 15P (pitch) changing that to a 13D 7P should allow the motor to recover the 2000 rpms that it's currently losing

1" less diameter = +400 rpms
8" less pitch = +1600 rpms

But as I stated above, I would ensure the motor is properly tuned first (before trying to determine the correct prop). You could be losing a good few rpms if it's been neglected...

Nice information Galamb. Keep talking, I'm writing a engine service and maintanance booklet.....lol

You will also want to make sure that the throttle plates are opening all the way.

You may have a misadjusted throttle cable, Along with running the wrong size prop, And possibly be in need of a complete engine tune up and engine inspection.

What size prop are you running?

Good luck with it.

You did buy the boat with the motor on it correct, and this was the motor the dealer installed on the boat. Why not call the old owner and ask what the max rpm was before you got it, that would help to clarify your situation a little bit more. Maybe call Mercury give them the serial number and see what warranty work if any was done on the engine, Maybe someone changed the gearcase along the way as well and a used gearcase with the wrong ratio would not help your situation either. Just throwin out some other ideas.

Agree with Dave, but I really wouldn't be surprised that an underpowered or improperly rigged boat was sold to someone who didn't understand what they were buying.

Companies like Tracker and Legend (in Canada) get you in the door with their glossy ads of a boat/motor/trailer package for thousands less than the competition.

What you find is an 18 foot fish/ski with a 50 horse 2 stroke on a trailer for 12K.

Of course, if you want the 115 Opti that should really be pushing the rig that's an 8K upgrade.

On a 22' "toon" such as noted above, a 60 bigfoot will allow it to "putter around" if it was fitted with a very low pitched prop (which was probably a special order, and extra cost and definately wouldn't be in stock until long after the boat left the sales floor AND nobody bothered to educate the buyer or ask his expectations).

This baby weighs over 2600 pounds (rigged) - add in a few passengers and you really do need the 135 horse (max hp rating for the boat) to even get it moving in the 20 mph range.

At least whoever originally bought it upgraded from the 40 horse that it was packaged with.

What irriates me is, did anyone explain or did a buyer do any research as to reasonable performance expectations or how to properly rig this - seriously, 60 horses to push somewhat over 3000 pounds being carried by a hydrodynamically inferior hull.

Fine if the buyer knew that 10 mph would be "flying"....

(that's my sermon for the day - sorry, sometimes have to vent)....

Johnny C said it best you get it, "One piece at a time" - LOL.