3.0l 115hp behind a 290 sp.....

[wyliec]

Hello all, trying to find a better prop for my boat, 1989 Sunrunner 195 cuddy. The original AQ151 was replaced with a 3.0l 115hp engine, leg is a Volvo sp-a 2.15 ratio. Boat is roughly 2500lbs, with two adults, gear and fuel roughly 3100lbs. Top end is 28mph by gps, at only 4000 rpm via boats tach. Calm lake, 40ft elevation. Prop is a stainless 15x19 3 blade. I know it's over propped, I need to be up near 4600 rpm. I am thinking a smaller prop might actually improve my top speed as well. Should I be reducing pitch or diameter, or possibly both?

 

[Maclin]

Just the Pitch.

 

[Maclin]

Oops, where are my manners...

Welcome Aboard!

 

[Sea Rider]

BTW, Welcome to Iboats,

Just 40 Ft of elevation ? if so, that´s nothing. Is 4600 rpm around the middle or max wot rpm range factory stated ? so to know how many pitch sizes need to drop to achieve that rpm.

Happy Boating

 

[jimmbo]

That’s a heavy boat for a little engine so 28 mph is actually it bad, but since the rpms are low(is the tach accurate?) the speed might increase slightly when the engine is repropped to run in the optimal rpm range. Don’t be too worried about diameter varing as the pitch changes, that’s more of a concern for the prop engineers. With some prop lines, diameter will get larger as the pitch drops, until it can’t get any larger. With others the diameter remains unchanged.

 

[wyliec]

Thanks guys. The max rpm is 4600, so I should be looking for a 15 pitch prop then? Would there be a benefit going to a 4 blade on a somewhat underpowered boat?

 

[jimmbo]

if you want to go slower a 4 blade will do that.
a 16" would be more what you need, a 15 will probably have the engine over revving

 

[Scott Danforth]

15p 4-blade would be my first suggestion, however a non-cupped 17p 3-blade may work.

 

[wyliec]

Thanks, I have found a brand new Solas 4 blade 14.75x15 on my local cl for $125 cad. I think I will give that a shot. I will report back with results as soon as I can.

 

[Sea Rider]

Whichever 3-4 blade prop you go after must be water tested on calm water cond and check if engine runs at least at middle rpm range, although max wot rpm range is preferred . Achieves best hole shot with slight less top end speed, you decide.

Report current max wot revs achieved as usually loaded with that Solas 4 blade prop...

Happy Boating

 

[wyliec]

No go on the 4 blade. Easily over revved, only did 21 mph, and made handling somewhat squirelly. However, my boat had a Stingray foil on it, removing it allows 4200 rpm and 30mph with the stainless 15x19p prop. I may try a 3 blade 17p out, or do you think a smaller diameter aluminum 19p would make a difference being lighter weight than tbe stainless?