Thanks for providing the URL to the Boston Whaler factory testing of a 150 SUPER SPORT with 60-HP engine.
Looking at the reported boat speeds obtained at various engine speeds, I have calculated the propeller SLIP for each:
RPM MPH SLIP
3000 14.7 19.6
3500 19.5 8.6
4000 23.3 4.5
4500 27.2 0.9
5000 30.1 1.3
5500 33.4 0.4
5940 36.3 -0.2
The value of SLIP tends to decrease as the engine speed and boat speed increase, which is completely expected and very typical. What is NOT typical is the values for SLIP are extremely low when the boat was at moderate planing speeds of 23 to 33-MPH, decreasing from 4.5 to 0.4. The SLIP values in this range are much lower than would be produced by most propellers. Finally, the SLIP at maximum speed has gone to a negative value, which is entirely unreasonable.
The general deduction from seeing values like this is there is an error in the data. The most likely error in the data is possibly that the propeller's marked pitch was understated, that is, in this case, the pitch is higher than "15".
Finding the actual blade pitch on a propeller is difficult with modern propellers because they typically do not use a constant pitch across the entire blade, but instead use a progressive pitch. So when the manufacturer marks the propeller as a particular pitch, he is, more or less, giving his assessment of how the propeller will behave in use, and this is also usually in relationship to other propellers in the same family and their "pitch" numbers.
The other data value used in the SLIP calculation that would have a big influence is the gear ratio. The gear ratio determines the actual propeller shaft rotation speed as a function of engine speed. A variation of a only 0.02 in the gear ratio would not produce a significant change in the SLIP calculations.
The final data value with influence in the engine speed, but here I will have to take the Boston Whaler engine speed data at correct, as they seemed to be measuring it with a digital readout, probably taken a value of engine speed sent from the engine's main control unit.
ENVIRONMENTAL DATA
The Boston Whaler reports notes the water and air temperatures were 82 and 86-degrees-F, respectively. Those are not favorable values that would result in better power output from the engine and propeller. Both engine and propeller will produce more more in colder air and colder water.
YOUR DATA
As for why your boat is not able to duplicate the performance seen from Boston Whaler's testing, there are only two possible reasons: more weight and less power.
The factory tested boat total weight was 1,779-lbs, of which "personnel" weight was 355-lbs. That sounds like two adult men. You can comment on what you think the total boat weight was during your testing.
The engine power output during the factory test is assumed to be 60-HP, as the engine was in new condition. The engine power output from your testing is really not known precisely. We can estimate the engine power output using the Crouch method.
If we assume that the factory data was exactly accurate, the 60-HP and 1,779-lbs produced a boat speed of 36.3-MPH. From that data we can deduce the hull factor as 198. That is a reasonable value for a hull with variable deadrise and only moderate V-hull form, as a value of 200 is often suggested for moderate V-hull forms at higher speeds where more and more of the hull is lifted out of the water.
Using 198 as the hull coefficient, the Boston Whaler test weight value 1,779, and your test reporting of boat speed as 31-MPH, we can infer the power needed to reach that boat speed was only 44-HP, much less than the 60-HP assumed for the factory test. That suggests the cause of underperformance is the engine. It could be in poor tune or perhaps the throttle cable from the remote does not move the throttle position to completely open at the engine.
Finally, the "dinged" propeller is also likely to be an influence. You need to re-test with a new propeller, get new data, and see if you can get closer to the factory performance values for full-throttle boat engine speed and boat speed.