Prop Research project

Hi all,
I have a thread regarding my research project with more info on the Virtual Propeller musuem forum, but I thought I may get a few more responses if I post what I'm doing here as well.


I've been making some progress on my research project. The topic is the efficiency and fuel flow rates of 3 vs 4 blade propellers. Any comments or suggestions would be greatly appreciated!

Research Proposal:

► Background: Propellers are vital in marine craft performance. The propeller is responsible for transferring the power of the engine into thrust. Without a proper propeller, engine power is wasted. There are numerous types of propellers. There are many characters that affect the efficiency of marine propellers. Such characteristics include rake, pitch, material, diameter, blade quantity, blade design, and cup. Many new boats that are purchased from dealers and manufacturers come with three blade aluminum propellers. It is commonly known that a four blade propeller is more efficient than a three blade propeller. However, it is not known exactly how much more efficient a four blade propeller is.

► Goal: My Experiment is designed to find the difference in fuel flow rates at given RPMs and speeds for three and four blade propellers.

► Materials: Test Boat: 1982 13’ Boston Whaler
Test Power: Tohatsu 30 HP 2 cycle outboard
Electronic instuments:
Fuel flow gauge
Tachometer
GPS

► Test propellers: I am working with Precision Propellers to create two propellers for testing. The props will be from Mercury. They will be aluminum. Precision Propellers will repitch the props with identical pitching blocks, to insure identical blade design, adding on inch less of pitch to the four blade (to compensate for the extra blade). The diameters will also be reduced and equaled.

► Procedure:
1. Install fuel flow meter and tachometer on boat.
2. Run various tests with three blade propeller
3. Record data
4. Run various tests with four blade propeller
5. Record data
6. Compare data and analyze results
7. Form conclusions


Then I will fill out charts. The charts I have so far are:
Speed vs. Fuel Flow(line graph)
RPMs vs. Fuel Flow(line graph)
Speed vs. RPMs(line graph)
Prop slip vs speed
Prop slip vs RPMs
Are there any other graphs or comparisons I should point out? Thanks.
-Ben

Id like to hear some comments on running the 4 blade with an inch less of pitch. Also why aluminum ? I just think you will get more consistency with stainless steel. Im not suggesting you change your procedures youve already defined, id just like to know what everyone thinks....:)