The correct size prop fitted to your outboard or sterndrive is especially important for both fuel economy and engine performance.
The best method to check this is, with a normal load in the vessel your engine should be able to operate close to its maximum rev range at full throttle. If the engine cannot reach maximum rev range fuel consumption will be poor and the vessel will be slow to climb up on the plane with the engine running under load.
The other end of the scale, if the prop is too small or badly worn down, the engine can over rev at full throttle.
Most late model engines have a rev limiter system which acts to interrupt the engines ignition system causing it to miss fire. Running an engine which is hitting the rev limiter is very hard on the internal engine, drive train, gearbox, etc.
Your local marine specialist is the right person to ask for advice on the correct prop for your boat.
Prop condition is also very important. Always repair any damaged blade surfaces and never use a prop with bent blades, as this will cause severe vibration and possible drive line damage.
Check your safety gear, jackets, anchors, expiry dates on flares, epirbs etc.
Don't forget, as the person in charge of the vessel you are responsible for the safety of everyone on board.
Happy and Safe Boating
Roger