Different RPM question

[gottabefishn]

I have a 1901 Mako with a 115 Merc Optimax ( bought Feb '07) It does not seem to get up in RPM's and runs WOT @ only low to mid 30's... I think 5500 RPMs is the max factory rec. If this is right why am I not getting more top end speed and higher RPM's ( I max out @ 5000rpm)
Thanks for any and all input

 

[rndn]

Re: Different RPM question

Is the motor mounted properly, ie: not too deep. Running okay? Just because it's new does not mean it's running right. Isn't it under warranty?

 

[gottabefishn]

Re: Different RPM question

It seems to be. Starts right up, nice and quiet, not smoke, no vibrations. Am I wrong in thinking I should be getting more RPM's and speed?
Thanks for your reply!

 

[hkeiner]

Re: Different RPM question

Perhaps you only need to change to a prop with less pitch.

 

[Silvertip]

Re: Different RPM question

Before spending money on prop changes, check the position of the antiventilation plate in relation the bottom of the boat. The AV plate should be even with to about an inch above. The AV plate is the flat plate directly above the prop. The dimension I gave is a "starting point" as you can continue to raise the engine on its mounting until you have optimized the setup. Just don't go so high you lose water pressure.

 

[hkeiner]

Re: Different RPM question

Silvertip is right. There may be other causes for your low WOT RPMs and you should certainly give those fixes that don't cost anything (or much) a try first.

However, if they are not successful and you later want to consider a prop change, you might talk to the guys at your local boat shop to see if you can check out a few props on a trial basis. My local Mercury boat shop let me check out a few different props for trial before my deciding on a purchase. In my case, I was considering a change to a 4-blade or 5-blade prop, as well as a change from aluminum to stainless steel. A prop purchased from a local boat shop might be a bit more expensive than if purchased on-line, but it is worth it to know ahead of time that the prop you do buy meets your needs...or solves a problem, in your case.