2006 115 hp 4-stroke Yammy WOT RPMs ?

I have a 21 foot SweetWater Tritoon Boat with lifting strakes. On it is a 2006 115hp 4-stroke Yammy with a 13.5" x 15 inch pitch prop. From the performance bulletins I have read for this type boat I should be getting at least 5800 to 5900 rpms at wot. I am getting 5200, what is robbing me of RPMs ?

Re: 2006 115 hp 4-stroke Yammy WOT RPMs ?

The WOT range for that motor is 5500-6000. Getting 5800 riding alone with no passengers would be the appropriate setup.

When you operated the boat and observed the RPM's, what was the load; number of passengers, gear, fuel load etc?

What is the brand and model of the propeller, aluminum or stainless steel? 3 or 4 blades?

The lack of RPM's is not the motor. It is most likely the propeller size and pitch and/or the mounting height of the engine on the transom.

A performance report is usually skewed to get the best performance so the boat is lightly loaded, <1/2 tank of fuel with no passengers in warm weather on a calm body of water. Was the report you saw for the exact year and model, similar weight and engine?

Re: 2006 115 hp 4-stroke Yammy WOT RPMs ?

Thank you for responding

There was about 12 gallons of fuel, 3 people (about 500 lbs), not alot of fishing gear, but I did have a troliing motor that takes 2 12v batterys, with 3 people (about 500 lbs).

The prop: Solas Amita 3 Blade Aluminum 13.5" dia. X 15" pitch SR

The performance reports were for a similar pontoon boats but not exact. Most of the perfomance reports I looked at showed the rpms between 5500-6000. The owners manual to my motor shows a 5800 WOT.

From what you are saying, I may need to get a different pitch prop or just leave it alone the rpms are fine ???

Re: 2006 115 hp 4-stroke Yammy WOT RPMs ?

The basic concept is to rig the motor with a propeller of the correct diameter and pitch so that when light, you reach 5800-6000.

If you plan to run >80% of the time with a load, prop it for that load.

Every model of propeller is designed for certain uses. Some props are 2 bladed (sailboats) or 3 or 4. I am not familiar with that brand. Also know going down in pitch and then switching to another brand is not always wise since propellers can have a different blade shape. Not apples to apples.

Basically, if you drop down in pitch, (2 inch increments) you will gain ~150 to 200 rpm's for each 2 inch drop if you stay with the same brand/model.

Before you go throwing $250+ at a new propeller, post your current setup and prop info in the propeller forum.

While some dealers will let you lend out props for testing, I have not found many who do it.

Pontoons may have certain attributes that are addressed by a certain type of prop. A dealer may be helpful.

Hope this helps.

Re: 2006 115 hp 4-stroke Yammy WOT RPMs ?

Yes this helps a lot. Thank you very much for sharing your knowledge and helping me on this.