i think its overspeeding

[xltier]

I have a 1994 225 aquasport with a Yamaha 250 ox66. when I take off it goes right up to 5200 rpms.as I climb up on plane I pull back on throttle to keep it from going to 5800-5900.rpm. when I am planed off I have about 1/4 throttle that doesn't seem to do much except make noise.should I be higher than a 17 pitch. not sure what the recommended rpm is for this engine.i am use to 4 cycle.sounds like its gonna blow up.i think this boat originally had a 200hp and this maybe the prop from that motor. ( there was 2 of us in the boat and about 60 gallons fuel.)

 

[JoLin]

not sure what the recommended rpm is for this engine.

That's the first thing you need to know if you're gonna prop it correctly. I did a little googling and came up with 5500 rpm, but do your own search or call a Yamaha dealer- don't take my word for it. Also saw mention of a rev limiter that kicks in at 6200 rpm.

IMO, you aren't hurting anything in the short term, but your revs are too high. Appears you're underpropped and need more pitch.

My .02

 

[porscheguy]

I’ve seen 5900 listed as the max on the ox66. And a range of 5200-5900. IMO, get as close to 5900 as you can. If you’re going well over, up the pitch.

What is the overall condition of your prop?

 

[Sea Rider]

Before venturing for a new prop from current one, need to make a hub slip test and check if that prop still performs opt, it's on its way or already with spun hub issues. Assume you know how to perform this simple test, must be done on flat calm water cond at full throttle.

Must know the correct min-max wot rpm range for that engine factory stated. Check if having a tech plate located somewhere on engine. Depending on what you find can go from there maximizing any other prop to suit best your boating requirements as usually loaded.

Happy Boating

 

[xltier]

the prop is in good condition.i think the thing bothering the most is that there is more noise increase between 5400 and 5900 than there is speed increase.but when I am topped out I can pull back the throttle aways without losing speed or much rpm.i think it is just free reving in the top rpm range if u know what I mean.my prop blades are cut flat across the back side edge where a same pitch prop on a different boat has wide blades. what is the difference.

 

[Silvertip]

Boat speed and rpm on a boat are not linear since there is always some slippage between the prop and the water. As you attempt to push the boat faster the drag increases, prop slip changes and at the very top end of the engine rpm range a rather significant rpm change may not translate to much of an increase in speed. Cars on the other hand are not dealing with slippage just wind resistance.

 

[xltier]

I have had a few boats in my life but never had one that I had to pull back throttle while climbing up on plane or it would go past 6,000.this is my 1st outboard.always been a mercruiser owner.

 

[Sea Rider]

If revs climbs fast or over revs when throttling towards full wot and top speed remains near same could have current prop hub on its way to become spun or already fully shot. To determine that, perform a hub slip test as a starter and go from there depending on what's been found. If engine is that old as the boat much worse. Prop hubs are not eternal..

Happy Boating

 

[xltier]

motor is a 2003.I maked the hub with a paint stick.doesnt seem to be any movement of the hub.it has a 17p prop on it. I guy has offered a 19p to try.ill post my findings.

 

[Sea Rider]

motor is a 2003.I maked the hub with a paint stick.doesnt seem to be any movement of the hub.it has a 17p prop on it. I guy has offered a 19p to try.ill post my findings.

Assume have removed prop, turned it over and marked a straight line across the middle of the prop body, went for a wot spin removed prop checked if the straight line remained same or has moved from where originally was marked, right ?

Have you checked what's the min-max wot rpm range factory stated ? Will know in over or under propped with current prop if found it's doing its homework right ? A 19 pitch will dial much less wot rpm than a 17.

Happy Boating

 

[xltier]

yes I marked it.