suzuki outboard prop ??

[cosergeant]

Hello, I have a suzuki 2005 70hp. At WOP I RUN 5,200 with a 3x14x11 alum prop.. It's on a 2005 crest pontoon boat. Top speed with two people is 18mph. When I load 4-5 people it drops to 14-15mph. The manual says the revs on this motor is 5,200 to 5,800. So, I am on the bottom figure. My friends tell me to get a 15" prop and top speed will be back to 18mph with friends.
but, won't that lower my revs below the recommended safe for the motor? If I buy a 9" or 10" pitch prop, that will raise my rpm to 5,400 or 5,600??? But, will my top speed be lower? Need help please....

 

[ahicks]

Your "friends" are all wet when it comes to their suggestion. If you want the boat to turn more rpms when loaded, you need less pitch, not more.

The questions then start. If you prop for your loaded weight, are you prepared to run at reduced throttle when lightly loaded? If you don't, you're going to be over revving your engine. OK for a minute, but not for extended runs. Your fuel mileage is going to drop/suck as well.

The other thing is, wondering if you are pulling anything with this 'toon (like kids on tubes)? If not, do you really care if the boat runs 15mph vs.18mph at wide open throttle?

If you think there's more than just a couple mph being left on the table here (with the prop and motor rpms you have now), you're in for a major disappointment. Toons are just not designed with speed in mind. They're ALL about cruising, and the prop you have on it now is likely just fine with that purpose in mind.

 

[Sea Rider]

Toon will cruise much better with extra 2-3 boaters on board with a less pitch prop than current 11 one,, the issue is that it's not known how much rpm increase the motor will achieve going per one pitch reduction, be aware that the near cast on stone that states -200 wot revs gain per one less pitch not always works on all boats. Other issue to consider is how often you'll be boating with 2 up and how often will be doing same with 4-5 up to choose a 10 or 9 pitch prop. Variable load i s a wot rpm serial killer, worse on a toon with a higher hull drag compared to other boat types..

Happy Boating