Top Speed Question

[PensacolaJason]

I've got a 1995 Key West Sportsman. It's 19.2 feet in length and has a 1984 115hp Johnson (J115TLCRD) mounted on it with a 12.75 x 21 SS prop. The boat is fairly new to me, so I wanted to see if my top speed sounds about right for my boat and motor combo. On smooth water without a lot of weight on the boat I can get around 30mph at full throttle. My average with a few guys and a decent tank of gas in light chop is more like 25 to 27mph. Not sure what the boat weighs, but I think the max outboard rating for the hull is a 150hp.

My question is, does this seem about right for my top speed? Is there anything I can do to increase my speed noticeably. Perhaps with a different prop?

Update: I found this attached chart on NADA that suggest my boat might be 1,500 lbs in weight.

 

[racerone]

Is the motor producing it rated power, yes , no or do not know ?----But for a 19 footer your prop may be too high in pitch.-----Try a 17" prop.----Is there a tachometer installed?

 

[PensacolaJason]

Is the motor producing it rated power, yes , no or do not know ?----But for a 19 footer your prop may be too high in pitch.-----Try a 17" prop.----Is there a tachometer installed?

I'm not sure if it's producing it's rated power. It has been to the shop, carbs cleaned and all new cables installed. I do have a tach that this same mechanic also installed, but it seems to work intermittently. It sometimes jumps around and other times the needle stays buried at 0 RPMS.