Boat speed under power

[Paul K]

I am the owner of a C-30 with a 25 hp Univerasl. The boat came equipped witha 3 blade 13X10 RH prop. I found that the performance under power wasn't what I would have expected. I changed to a 2 blade 13X11 with some improvement. What is the correct size and pitch for this boat.Thanks,Paul K

 

[Kevin]

props

Hello Paul,Our records show that the two correct propellers for your vessel are the two that you list. I’m not sure what speed you are trying to obtain is, but as long as the propeller is loading up the engine properly I would guess that you are not going to see much additional speed. If you find that the propeller is not loading the engine up then increasing the pitch in 1” increments will help to distribute the available torque and help you obtain additional speed.Hope this helps Kevin

 

[Wayne F.]

Universal M25 Prop

My boat has a Universal M25(21HP)which used to have a 16X9"RH two bladed propellor. This combo pushed my O'Day 35 to 7 knots. I recently switched to a 15X8" three bladed prop which is smoother but doesn't quite push the boat as fast.I'd say if you use a prop in the 16" diameter range(assuming you have the hull clearance for it-a couple inches clearance at least)the boat will perform better than with the seemingly undersized prop you have now.Also the 11" pitch you have may be dragging the engine RPM down too much. My boat was a little low on RPM with the 9" pitch.Of course the higher the pitch the more the engine is lugged down and the lower the pitch the faster it will turn-it's a bit of a balancing act.The engine should turn at full rpm with the prop digging in at full throttle(approx 3000rpm)Then you would just cruise at a lower RPM which gives you full power available when required.

 

[Garry @ S/V TASHTEGO]

Gerr's Propeller Handbook

Go get a copy of Dave Gerr's "Propeller Handbook," $18 from Barnes and Noble, and be your own expert.

 

[Dave Fremont]

Catalina 30 Prop

I too, have a Cat (88) with M-25XP engine. I purchased the recommended 13X10 three bladed prop from the Cat dealer in Vancouver as that was the one he said was specified by Catalina.The 13X10 does not put the proper load on the engine, I only do 4.9 k at 2300 RPM. My friends exact same boat does 6.1 knots at 2300, (tops out at 3000) with a 15X9 three blade. Check out the archives, this has been verified by others.I too, have a 30 Cat (88) with the M-25XP engtine. I purchased the recommended 13X10 prop from the Cat dealer in Vancouver as that was the one he said was specified by Catalina. The 13X10 does not put a proper load on the engine I only do 4.9 knots at 2300 RPM. My friends exact same boat does 6.2 knots at 2300 rpm and has max RPM at 3000. His prop is 15x9 three blade, (there is room to swing it).My Cat dealer gyped me by not doing his research. Check the archives, this has been verified by others.