Yes, you are correct. Two different sizes they are sold as a set. Others run larger props on this boat with different power options some run B5 or B6. The C series C4, C5 or C6 stand for stainless. This is the first boat I have had with duo props and I am amazed at how these props push this heavy boat along. The nice thing about the Volvo or Bravo duo system is they are tough enough to take a high torque diesel power plant. A lot of though and engineering went into the development of this design.
Some of the high end boats have went to the ISP drive. Wow
Threaded Mode