Why is it that a boat prop can cut revs on a motor, but th same motor in a car(once moving) can rev to its max

Question

Due to a propellor that has too much pitch, it will not let a motor rev right out as if it were in a car.

Answer 1

You have really answered the question yourself. In a boat the prop places more load on the engine then it has in a car. This is not to say that if you reduced pitch some you would not get the same rpm as the same engine in a car. But besides the pitch of the prop, there is the gear ratio. An inboard boat commonly has a gear ratio of 2-1 and thats it. A car not only has a transmission with multiple gears but also a differential that reduces load on the engine and may have a ratio of 3-1 and much lower (like 4-1 or more). So the cars torque is multiplied many times while a boat is limited. You may get the same performance in a car if you tried running up a long steep hill in top gear, chances are it would not reach max revs becuase of that load. A boat is said to be running up hill all the time.

Answer 2

Because water is restricting the props movement, if a car was in gear it too would restrict the revs of a car engine.

Answer 3

A boat engine is under constant load.

Answer 4

The way with an outboard you can't rev once you're in gear? Because theres no reason to. Theres no gears on a boat motor.

Although I suspect it would be possible, I believe it is restricted by a mechanism in the throttle, actually, I know its restricted by a mechanism in the throttle. You can only use you're rev lever while in neutral.

In a car you need to be able to rev (in a manual) so that you can change gears, use heel toe, etc etc.

Although from recollection, theres no way of reving while in gear in an automatic? same principle I suppose.