Also, how did the boat do getting up on plane? If had a hard time could have a partially slipped hub (especially if prop indctates strike marks), but doubt this is the issue if still hitting 39mph.Without repeating what's already been said about 4 stroke vs 2 stroke, I have a 1996 208, with a 150hp 2 stroke yamaha saltwater series II. My top end with half a tank of gas and just me on lake like conditions was 39.0 mph. Add people and gear and I am still up to 37/38 mph Hole shot is good on the 2 stroke, and I get up with no issues (trim tabs would certantly help though at slower speed staying on plane, not sure if you have those). My boat is painted and has dropped a mph or two since being in the water all summer (algae and barnacles).
I would think you should be up in the 42/44 mph. Maybe see max rpms om your engine and see what your turning, may need to adjust prop (no clue what pitch is on mine).
Also, how did the boat do getting up on plane? If had a hard time could have a partially slipped hub (especially if prop indctates strike marks), but doubt this is the issue if still hitting 39mph.
Double check and make sure your not reading in knots (39 knots equals 44 mph which I am guessing would be about right).
Boat is in the water so may be tough but will see if I have numbers on the prop (came with the boat).Seems to get up on plane fine.
Using my GPS in mph, and thought I would get over 40 mph. Curious what prop sizes folks use.
I don't get 40 mph on my 208 with 150 SX. Even if I could, I wouldn't run at WOT for long periods.
As long as you get on plane OK with typical loads, I wouldn't fret over top end. Note also that that motor uses almost twice as much gas per hour at WOT as it does at most efficient cruise revs which are in the mid 3000 rpm range (say 33-3700 revs). I usually cruise at 3800 to 4200 revs depending on seas and wind.
As to the comment on a slipped prop; If the hub is slipping, it will do so at the higher torques like getting on plane and if it is actually slipping (as opposed to having slipped and then froze in a new position) when you apply load you will see the revs race higher without any increase in thrust or even perhaps a decrease in thrust. If the hub sliiped into a different alignment, you may feel vibrations especially at lower speeds.
