Pontoon Boat & Deck Boat Forum

Checked out 19 pages on a search with no luck.

Here's the problem.. 1999 Suntracker, 21' Party Barge. 1999 90 H.P. 2 stroke Merc. Running a 13-3/4 X 17 Vortec prop. WOT is 6100 RPM. Engine is supposed to be in the 5000 to 5500 range. My question is .. Will a 19 pitch bring the R's down in range or will I need to go to a 21? This is light load with 3 adults and small child... Don't have a speedo or GPS so no speed is known. Any suggestions?

Are you sure your tach is correct? A 17p on a 90 HP motor sounds like too much prop and shouldn't give you that rpm unless the prop is slipping or cavatating.

Carl might be right about the tachometer. You might want to have it checked for accuracy.

The current Mercury 90 hp 2 stroke is running a 2.33:1 gear ratio which would mean it may use a propeller with high pitch.

FYI: A Mercury 115 hp 2 stroke has a 2.07:1 gear ratio and they'd run a lower pitch prop since the prop's turning over faster. I

But if your tachometer is correct, you probably need more pitch to bring the rpm's down to 5500 ish.

Just remember, for every inch of pitch you adjust, you will effect your RPM by about 200.

OK, Houston, we have a problem. After borrowing a gps, I find wot speed is 14.3 mph. tach is reading 6100. Upon idling down and kicking out of gear, tach is reading 2000. First problem first, I got to get a new tach. Then back to the prop.....Thanks all...

Most outboard tachs have a switch on the back for you to set the number of cylinders the motor has. You may want to check that before replacing it. Even if it is set right I would change it and then change it back to see if that helps.

Never gave the switch a thought. Good idea. Also have a strong suspicion that the hub is spun on the prop. Even tho it is new.
Has anyone had an trouble with the hub on the Vortec props.

yep, check the switch on the back of the tach. Mine was set wrong when I got my toon.