1972 Columbia 30' with A-4

[EugD]

I have the boat on the hard and am faced with whether to change my existing 2 blade (16x12) propeller. I can not understand why the previous owner would have chosen this large a size when all I read suggests a 2 blade at 12x6, 12x7 or 12x9. I also have seen Indigo's 3 blade winged 10x7.4 and Michigan 3 blade 10x6 and am inclined to go with a 3 vs. 2 blade.

My prop guy says that the rule of thumb is that if you are using a 12x9 2-blade that the appropriate 3 blade would be 12x8. He seems concerned that we will get too much RPM for the A-4.

Anyone have a definate opinion?

[Don Moyer]

Hello,

Before changing to any other prop, we need to hear whether or not your engine has a 2 to 1 reduction gear. If it does, then a 16 X 12 two-blade prop wouldn't be all that unreasonable.

If you have a tachometer, it would be useful to know what RPM you're able to achieve.

The prop sizes you're mentioning are only appropriate for a direct drive Atomic 4.

Don Moyer