not accel as I think it should

Hello. I bought a 99 nitro 185 sport with a 120 2 cycle force mercury. My concern is when I am taking off it revs under load to 3500 then shoots to 5500 with no more thrust. It does not slow down, its still accelerating but just not any different. It does take a bit to plane out. The best way I can describe it if the prop is pulling in air allowing the load to decrease and the engine to rev. Once it planes out the rpm drops to say 4800 and you are running 30 with about 10 more to go before it maxes out. I (not knowing boats that well) was thinking a dolphin tail might help if it is in fact pulling air into the prop. Anyone have any good suggestions? Or what I might do to test it.

Be sure your trimmed all the way down on take off

May need a prop with a little more pitch

If it is pulling air, a fin might help. I agree with "G" though, prop with a little more pitch may also help.

I would also have someone look at how the motor is hung. Trimmed all the way out may not leave the motor at a 90 degree (or proper angle) to the hull. Might be as simple as that.

Make sure the motor is mounted as low on the tramson as it can be.

Sure prop hub not slipping ?

If it used to run better set up the way it is then I am with Nimrod of the hub may be slipping.

Quote:

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Originally Posted by NIMROD

Sure prop hub not slipping ?

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This would be my first guess also.........mark the hub/prop with a permanent marker then go for a ride, check marks if they have moved you know it's a spun hub.

Also I would think a foil would make the problem worse as a foil lifts the stern of the boat.

Does the boat have a jackplate on it, maybe the motor is lifted a tad too much

Thanks for all the ideas I appreciate it. I'll mark the hub to make sure. I am stumped on the prop however. I went to Mercury marine and went thru the prop selector as I was curious to see if I had the right prop to begin with, but all it gave me was their recommended replacements. It is a Lazer two and the numbers on it are 48-16990 and the pitch is 20 any ideas?/

Whatever the pitch, it shouldnt be revvin like that...its either the prop hub is spun or your cavitating. the first set of fins right above the prop (anti-cavitation plate) should be level with the bottom of the boat - as a general rule to start. You can gradually raise to give you more top end speed. Until cavitation becomes an issue. Same with trimming - take off with it all the way down, then gradially trim up once on plane till you hear the rpms increase - then back down a hair and youre in the zone. Of course all this varies with different boats.. it takes lots of experimenting and adjusting till you get it right.

Does your prop have holes in front of the blades? Some motors don't like those vent holes.

If so, try just flooring the throttle from standstill and see what happens. My old Evinrude hated the vented prop unless you floored it, and then it would spin for a second or two, then leap forward like being shot out of a gun.

i got tired of that, and filled the holes with epoxy putty. After that, it accelerated a little slower, but would not spin out, so it was much more controlled.

Check for vent holes and let us know what happens.

-TH

What's the max rpm you can get?

Jack sounds like a slipping hub to me. See if some one up your way has a Merc Prop you can borrow for a test run. A 14 X 19p is a common size that would work for the test.