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WOT - RPM - Prop pitch

L

Lowen

New member
I am running a 2014 30HP on a heavy displacement hull, with the 11" pitch prop as supplied my WOT is only 3500 RPM but the boat will cruise at about 5 knots (my preferred speed) at about 2000 RPM.
Is this doing any harm to the engine?
I have purchased an 8" pitch prop and this will allow 5500 RPM WOT but at the speed I prefer (5 Knots) engine speed is 3000 RPM and the overall effect is more noise and presumably fuel consumption than using the original prop (11")
What would you recommend?
 
2 cycle or 4 cycle engine?...what is the comparative speed at 2k rpm?...if it is a 2 cycle i would go with the 8 inch one because it will run the full range of rpm's....a 2 cycle is not designed to tun 2k rpm's all the time without opening it up for a bit....as far a gas mileage is concerned you just have to check it and get the difference and decide how big a factor that is to you..

if its a 4 cycle i would still lean to the 8 inch prop but the exposure to carbon build up is less because you don have oil in the fuel....
 
papyson said:
2 cycle or 4 cycle engine?...what is the comparative speed at 2k rpm?...if it is a 2 cycle i would go with the 8 inch one because it will run the full range of rpm's....a 2 cycle is not designed to tun 2k rpm's all the time without opening it up for a bit....as far a gas mileage is concerned you just have to check it and get the difference and decide how big a factor that is to you..

if its a 4 cycle i would still lean to the 8 inch prop but the exposure to carbon build up is less because you don have oil in the fuel....
Click to expand...

It is a 4 cycle MFS 30B. Do you think that running at 2k rpm with the occasional spell at WOT 3.5k rpm will do the engine any harm?
 
Thanks for your input, I will do a little more experimenting, certainly the engine response using the 8" prop is much sharper.
 
the 8 inch will be much safer in case of unexpected rough water and wind...you are going to use more gas with it but its the only way to go in my opinion...
 
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