New boat...new engine...RPM question

[bcs1313]

I took my new boat out yesterday for the first time. 18' Qwest pontoon boat. With three girls under 7, pontoon was the way to go and we primarily will be on a local 9.9 lake so we have a 9.9 merc on the back. I was going through the engine break-in process, but was really surprised when I started getting to 3/4 and WOT and the RPMs (according to my gauge) never got over 3,000 RPMs. That can't be right. Any ideas? With my dad and one daughter and a full load of fishing gear and food/drinks we were going about 7.5mph WOT. Which isn't that much less than what I expected (somewhere around 9). But I thought WOT RPMs should be between 5-6,000.

 

[sutor623]

Re: New boat...new engine...RPM question

This is the 9.9 that you are talking about? Is this motor designed to be used on pontoons, or for a jon boat? I have heard of companies using different gear ratios or different sized props(high thrust) on pontoons. Sounds like your prop is too large for your application. Also, are you supposed to be over 3/4 throttle in break in period?

 

[bcs1313]

Re: New boat...new engine...RPM question

Second hour of break-in period on this motor includes 10, one-minute WOT runs. And this is a 9.9 big foot Merc designed for pontoons,etc. Not a kicker or jon boat motor.

 

[sutor623]

Re: New boat...new engine...RPM question

Okay well I am glad that you have the right motor Does the handbook tell you that WOT is supposed to be higher? 7.5MPH with that much of a load sounds excellent for a 9.9.

 

[sutor623]

Re: New boat...new engine...RPM question

Gear ration is 2.42:1 correct? Give me your prop pitch and I can tell you if your RPM's are being read accurately.

 

[MH Hawker]

Re: New boat...new engine...RPM question

I suspect its way over propped, I also run a 9.9 on a 20 foot toon and get around 12 MPH GPS with me and the wife, how ever I am running a standard 9.9 mariner with a 2.0:1 ratio and the Bigfoot should hook up a good bit better to the water. But I would wait till the break in period is over before I push it to much, but talk to the dealer and make them aware of the issue so they can sort it out. And as a guess you should be running a 9 pitch. I really enjoy a 9.9 lake its more peacefully and the people are plain more friendly and with no bass holes or jet fleas I am sure you will to.

 

[steelespike]

Re: New boat...new engine...RPM question

Your prop size will be near the base of the blades or under the prop nut.

Big foot is 2.42. And no tests of a big foot. on the merc site.