rev-limiter does not kick in when it should, or boat tach inaccurate?

[rayaa3]

Hi Folks -

My engine is a 2007 Merc Optimax 150XL.
My boat is 2006 tahoe 215 OB.

It's a recent purchase.

I noticed during my test drive, and since having the boat that my rev limiter does not kick in until well past 6500RPM...I would say some place around 6800RPM. The alarm goes off, and if I back down all is fine. If I don't I get backed down to about 5000RPM.

All of this is according to boat tach on the dash.

The advertised WOT range of the opti is 5250-5750. I am wondering which of these is true:

1) the rev limiter does NOT kick in and limit you at the advertised RPM range limit? It only kicks in when you are REALLY about to screw the pooch. So - Ray, you need to trust your boat tack and keep it down to 5750 or lower.

or

2) my boat tach is inaccurate - because the onboard computer is not kicking in and stopping me, and it will do it at 5800RPM...so the fact that it isn't really just means my boat tac is wrong. So ray - you can trust the rev limiter and safely run at 6250-6500 RPM where the rev limiter hasn't kicked in yet.


or if there is a 3rd likely possibility.

I just bought the boat and took it in for 300hour service (it has 250hours, but you never know what the last person did).

The symptom described happened before and after.

The boat came with a 15x17P prop on it, and another 15x16P 4 blade prop that had never seen a hub. I tried both props, same RPM (or so very very close that it was impossible to perceive a difference). I did lose a little top end on the 16P prop, but that was expected, and I gained a little hole-shot.

All the testing described was done on calm water, with only myself aboard. Will be interesting to see how thing run when I have her loaded down with family and ice chests.

thanks for any help or advice on above.

 

[GA_Boater]

While the shop has the boat for service have them verify the tach. They should have a shop tach for testing stuff just like this.

 

[rayaa3]

I just got it back from the 300 hour service. Didn't realize at the time I took it in how far off the tach seemed. Trying to avoid another visit. Hoping someone can confirm for me that the limiter does kick in at 5750-6000 - which would confirm that my tach is inaccurate, and #2.

 

[QBhoy]

Hi.

That engine shoild have a rev limiter. Does it not have smart craft ? That or the vessel view will tell you exactly what rpm it’s doing. Tachometer are usually off, but perhaps not by this much.

 

[rayaa3]

No smartcraft. I've heard of vessel view, $200ish bluetooth reader for your phone?

At what rpm are other folks optimax over rev limiters kicking in?

 

[GA_Boater]

At what rpm are other folks optimax over rev limiters kicking in?

It depends on how accurate the tach is. Your rev limiter is probably working right, it's the inaccurate tach making it look wrong.

 

[GA_Boater]

You really should get your tach verified. A fairly accurate tach is needed to dial in props things like this when the limiter is kicking in.

 

[rayaa3]

Little follow up. Got behind the tach. It was set to 5p not 6p. I wont know till next week end but bet that was it. The math adds up perfectly.

 

[GA_Boater]

That'll do it every time. :smile: