Prop size Yamaha 115

bcastlebbcastleb Posts: 9 Greenhorn
I have a 1999 1720se with a 1999 Yamaha 115 2 stroke and jack plate. The prop that I have now is a 17" Stiletto 3 blade, with the jack plate all the way up, my rpms are 6200 and speed in low to mid 30s. I purchased a Powertech RXB4 18" and with the jack plate all the way up 5600rpms at 32mph, jack plate all the way down I'm at 4800rpms and 40mph. Having said all of this, I'm hoping someone with this setup or similar can help. I understand I can't have high top end speed and run shallow. I have filled out the prop worksheets and spoke with some Powertech guys and just wanted some real world experience.


  • dholleydholley Posts: 91 Greenhorn
    You're inducing lots of slip into the equation when you jack it way up. Are you also using the trim, or just the jack plate? With the 18 pitch prop you're at 3% slip (really efficient) vs jacked up at 33% slip (extremely inefficient).

    In my opinion, the boat needs to be propped to hit max RPMs (5500 in your case) without inducing tons of slip. Sounds to me like your either overpropped or not trimming the motor to obtain more RPMs.
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