9'6" inflatable too slow with Yamaha 15 hp

[jimmyboy82]

I have a 9'6" inflatable when it is loaded heavy I can only go very slow far from being able to plane. The boat has a Yamaha 15 hp what propeller would be best?

 

[steelespike]

Re: 9'6" inflatable too slow with Yamaha 15 hp

A 9'6" inflatable has a number of things going on.Usually not a particularly efficient hull shape,not much area to help plane a load,The motor may be too low in the water, if inflation is not right and a less than ridged keel the hull shape will distort from the weight and motor thrust.We need more detail.What is" loaded heavy"?
What prop is on it now?Numbers are usually on the barrel or under the prop nut.
What year motor and 2 stroke or 4 stroke?
You really need a tach to tell if its propped right with a light load.A Tinytach is about $47 and easy to install.A gps for speed would be very helpful as well.You shouldn't make a prop change without a tach.

 

[jimmyboy82]

Re: 9'6" inflatable too slow with Yamaha 15 hp

The prop numbers are 9-1/4 diameter 10-1/2 pitch and that is the factory installed prop. The motor is yamaha 15 2 stroke 1997 short shaft model and the boat has a soft bottom which is always maxed out with air. With 520 pounds the boat reaches top speed and with another 125 pounds the boat will not plane unless catching open ocean swells. I do not yet have a tachometer.

 

[steelespike]

Re: 9'6" inflatable too slow with Yamaha 15 hp

have you tried trimming in with a load? Your boat is probably pretty light
thus your prop is pretty high up the chart with only to props higher.
Being so little and with a less than ridged hull it will be sensetive to amount of weight and placement.If you get a tach you can tell if you should change props
and what your results are.Its possible a smaller pitch will help but you may have to watch the rpm when lightly loaded.Lightly loaded RPM and speed is very helpful in telling if the setup works.