Does this setup and speed sound right?

[medicbearusaf]

I have a 86 larson 17.5 open bow. 3.0 mercruiser original engine. Seems to run fine. Have a 15x17 3blade prop on it and with me and 2 kids nothing else in the boat relatively smooth water today at 4500rpm Speedo said between 28 and 32 mph. But mostly right at 30... Reading other posts I feel like I should be able to go a little faster. Maybe I'm wrong. In still learning.1

 

[Alumarine]

Speedo's aren't that accurate.
Use the gps in your phone.

 

[alldodge]

The issue is your tach and speed-o may be right but more then likely their off a little. If I use a 1.94 drive ratio and 30 mph it comes up with about 20% slip. The 20 % with a 17 footer is a bit high.

Things that can cause slip
Dinged bent or damaged prop
Hull is not clean
Boat has extra weight due to gear or water soak
Incorrect trimming of the drive

 

[roffey]

I think for the RPM the speed is most likely close. You should be at 4800 rpm.

https://www.mercurymarine.com/en/ca/engines/inboard-and-sterndrive/mercruiser/30l/