WOT at 5,000 rpms

[JJags3]

I have a 20' Aquasport CC with a Johnson 112. It runs really great at all sppeeds. WOT is dead-on 5,000 rpms. It has a 3 blade aluminum prop with 17 pitch. My question is, should the rpms be closer to 5,500? Do you recommend a lower pitch, say a 15 or 16? Or am I good as it is? Thanks

 

[jay_merrill]

Re: WOT at 5,000 rpms

Depends on who you talk to. Some will tell you that you are lugging your engine and that you will have problems as a result. Some, including my OMC dealer, who has been working on outboard motors for 30 years, say its fine and not to worry about it.

I guess that the best thing that you can do is to surf the net for as much info on the topic as you can find. From there, you can make your own decision.

One factor that I do think you should consider, is whether or not your prop choice is correct for your typical load. If, for example, the WOT rpm is 5,000 when the boat is lightly loaded, but you normally take lot of people and gear with you, I would say that you probably need to go down to a 15" wheel. On the other hand, if you are checking the WOT rpm in your normal operation configuration, you might be just fine.

 

[Silvertip]

Re: WOT at 5,000 rpms

Changing props is the "last" thing to consider when trying to optimize performance. Is the hull clean, is the engine making full power, is the throttle opening all the way, is the boat full of water soaked foam, and probably most important, where is the AV plate in relation to the bottom of the boat. In other words, raising the engine -- so long as you don't go so high as to lose water pressure, may bring up RPM several hundred RPM. We are not talking trim here -- I meaning physically raising the engine the engine on its mounting. There are lots of posts you can read in the Propeller forum on this topic. Lastly, the style of prop you choose can have an effect as well. A 19P prop from two different manufacturers may not and generally do not produce identical performance characteristics. One will have better hole shot and the other will have higher top end for example. So optimize setup and then consider props. That motor can handle 5500 and actually likes to run there.