help with prop selection

[galynd]

I recently helped my brother put a rebuilt engine into his 1978 model Catalina 30. We removed the old Atomic 4 and replaced it with a Yanmar 2gmf, knowing it might be slightly under powered. The engine runs well but it only pushes the catalina about 4 knots maximum speed. We're hoping to gain some speed by optimizing the prop. I don't know what prop is on it now as it's in the water. However, the transmission is a KM2A, with a gear ratio of 2.62. What would be the best prop selection for the boat?

thanks.

 

[Bob4203]

Thats a good question. I have the Universal M-18 (2-cylinder) that puts out about 12-14 horsepower. As such, the standard two bladed prop running against a swift current and big tidal changes say, in the Carolina's or Georiga, would leave me going nowhere at high speed! A three bladed prop might provide the extra torque or more push then a two bladed prop. I always thought there was some magic formula to prop selection only known to the prop experts. You know, pitch formulas passed down through the generations! Maybe someone will chime in and give us the skinny on what works best on a two cylinder diesel for the 30 Cat.

Bob
'88 Mark II
Georgia

 

[Bad Obsession]

There is no problem that money won't fix. You could always go with the Max Prop and talk to the company. Give them the engine and transmission and they will tell you the best solution.