Prop question

[tenacrewoods]

I have a 14'X 6 Alumacraft Jon Boat,I've added front and rear casting, 1/2" floors, two deep cycle batteries,5 rod & reels and accessories.With myself and all gear im pushing 1000 to 1100 lbs.I was running a 20hp Merc not sure what size prop but boat ran at 21 mph.I sold 20hp for 40hp Tohatsu w/heavy load prop around 11 x 8 and I only got 22 mph,has great hole shot but no to end. I'm thinking of buying a 10.5 x 13 for light loads and was told I would only get about 5 more mph. Is this true,I would like to get about 30 mph.What can I do. Motor is 1995 40hp M40C.

 

[Spidybot]

Re: Prop question

Hi tenacrewoods <br />Is your motor 2 or 3 cylinder?<br /><br />According to Tohatsu's prop chart, the 3-cyl will cope with a 15" pitch thus giving a theoretical top speed above 30.<br />If you visit www.tohatsu.com and follow the links 'Accessories' - 'Prop' etc. you'll see what's available. They do not give info on speed, but www.mercurymarine.com does. Although brands cannot be compared just like that (due to different gear ratios), you'll get an idea.<br /><br />Both the weight and boat size has to count in these calculations.<br /><br />Third party props may be available in different pitches, but I think you won't need any higher than 15" anyway.

 

[Boatist]

Re: Prop question

All I can say is that is a funny prop for a 14 foot boat. Seems like too low a pitch for a 14 foot boat. My 14 foot has a 15 hp motor and has a 9.5 x 10 prop and does about 18 mph. With a 40 hp motor I think you should have at least a 13 pitch. I guess you have no way to mesure RPMS of motor.