Underpropped, how far up should I go

[spitfire9au]

Just repowered and on the first run today had awesome acceleration and holeshot. No signs of cavitation or ventilation. From a standing start hit 6000rpm in mere seconds, around 32 knots when I backed off for fear of over revving.<br />Boat is 5.8m plate ally centre consol, motor 140hp Yamaha, 1991. Current prop is 17" ss. As far as I know it's just a standard prop. <br />Question is, anybody have any idea how far up in pitch I'd need to go to prevent over revving?<br /><br />Thanks,<br />Jeff.

 

[walleyehed]

Re: Underpropped, how far up should I go

6000 ain't over-reving by no means...did you have it completely wide open???<br />We need to know Brand of prop if you would please.

 

[spitfire9au]

Re: Underpropped, how far up should I go

Was wide open but was still accelerating when I backed off at 6k. Felt like rpm would have gone much higher, how high though is only a guess. Redline on the tach, genuine Yam one that came with the engine, is 5500. How high can you safely rev these engines?<br /><br />As for the prop brand, sorry can't find it. The only markings on the prop are 13-17k. Don't know what the k means but presuming the numbers mean 13" diam by 17" pitch.<br /><br />I'm not after maximum performance, boat is used mainly for fishing. Just want to get into the right rpm range so it doesn't get accidentally over revved, if that makes sense.

 

[walleyehed]

Re: Underpropped, how far up should I go

If you don't know how much higher than 6k it will go, we have no reference as to what to recommend.<br />see if you can borrow a 19 pitch and run it...WOT, and get some numbers with that.