What are the loses due to boat propeller wear/damage?

Question

I'm wondering how much thrust/horsepower/speed (whichever is more relevant) you lose by having chips, dings, scratches, bent sections etc on your propeller. A quantitative answer would be preferred over a qualitative one. Percentages or deltas would also be helpful.

If it is more appropriate, given the example of a prop on an inboard/outboard boat with a dime size piece missing from one of the propeller blades. The shaft diameter is around 5" and the blade tip diameter is around 15".

Answer 1

Ok , your prop has a few chips or nicks on one ore more of the blades. Do you have any vibration upon acceleration ? Has your ability to get on plane seem to take longer ? Does your boat want to pull to one side or the other ? All of these questions pertain to your prop, and it`s condition.  You can have your prop rebuilt back to O.E. specs at a reasonable price. Or just replace it with a new one. Ask yourself what kind of performance you want . You can get a prop of any flavor. Hole shots or top speed and other various designs. Check with your local Boat shop or any Boating magazine. As to how much power your losing, just depends on your set-up. It` kind of like losing a cylinder on a V8 you pay for 8 but only get 7.

Answer 2

This is a very good question.  However, there are few studies that are "public" that have been done on this.  The Naval Research Lab, at Carterock, Maryland has done extensive design studies on propellers.  I think it's fair to say that because each Boat, prop, and engine is different, it's hard to put quantitative numbers on performance.  Keep in mind that the forces required to chip an alum prop could bend that one blade, without bending the other two.  

      Strictly from experience, I've seen performance increases of 15 to 40% by changing props.  True,  the larger increase was a double switch, to stainless, plus a different pitch from the original damaged prop (bent blades).   It's a fact that design changes (thinner blade cross-section)  make stainless props about 15% more efficent

        The hub dia. of 5" is about standard for outboards and IO's and 15 to 17" tip to tip, but it is the pitch that really makes the differance.  Thats the distance the tip travels in one revolution.

Answer 3

A 1/2 inch hole in a propeller can reduce thrust by about 3%. It will also cause wear on the shaft bearings because the prop is out of balance. Eventualy the prop blade will fracture and drop off due to cavitation and lateral forces. This will cause a violent vibration at medium to high speeds and result in shaft failure if not repaired.

Answer 4

Hey I would not be operating a boat that had a damaged propeller. This can cause so many bad things to the motors it's just not worth it. Example $150.00 prop or $5000.00 motor. Once the motor is gone the boat is pretty much worthless.

Answer 5

Sorry, I am not going to give you the scientific delta and matrix answer you are looking for.

Here's what I will share: if you have a balanced prop and you lose weight from one or more blades that thing is going to flail around on the shaft. Do that long enough and you will blow your seals and risk losing your lower unit.

Seen it happen more than once.