What is the disadvantage and/or advatage to a 4 blade prop vs. a three blade?

Just bought a scarab 29 1998 with twin 350 carb engines. What prop would you start out with on this application?

Three blade will be better WOT but the four blade will give you better cruise and all around performance. With 350's I would say try a 22 or 24 pitch bravo one four blade. Look in the scarab owner section and someone might have your exact boat and be able to tell you what they are running.

A quick search shows that the 23 mirage or mirage plus is what others have been using http://www.offshoreonly.com/forums/s...do-you-do.html

Sometimes the 4's are slower as mentioned, but not always. It will depend on the difference between slippage between the current ones you are running and the new ones. There is a lot to propping. Rake, Camber, pitch & diameter are all important too, not just how many blades are on the wheel. I have had some boats run faster with 4 & 5 blade props than with 3's. It is all in the prop and the way the boat is set up.. Unfortunately there is just some trial and error about it.

If you are running 3 blade mirage + props now I would recommend starting at subtracting 1" of pitch and trying a Bravo 1 4 blade prop. Or possibly staying the same pitch and trying merc revolution 4s as they are kind of like a mirage plus version of a 4 blade..

Jamie / Lakeside

The first thing I would do is to run the boat with what you have and see what kind of rpm's you get and speeds mon a gps .Then you will have a guide line to what you need to run,weather or not it is a four blade or a three. My friend had the same boat and for the best top end speeds the mirage plus was the best.The drives on that boat are pretty deep in the water.But first run the boat.

I'm gonna hafta disagree with baywatch. I think a 22 or 24 4-blade will be too much prop for those 350 motors. If I were gonna guess...I'd say you should be in the ballpark with a 19p Mirage...or Mirage Plus (3 blade) sir.