30hp 4 stroke Tohatsu max RPM

[Geezer1]

So I'm a little confused by the max rpm numbers posted in my owner's manual, specifically that max rpm is between 5250 and 6250 rpm. What exactly does that mean? That max rpm can be anywhere between those numbers? Should I strive to prop the boat to run max at 6250 rpm?

 

[pvanv]

What is your actual model? MFS30A? Yes, that is an acceptable range for WOT RPM. You want to be near the high side... say 6000-6200.

 

[Geezer1]

Actual model is MFS30C Paul. I've got a Tohatsu 9.9 x 14P prop on it now which at WOT is turning 5900 RPM and reading 29 MPH on GPS. With the 2.17 gear ratio, that figures out to be about a 20% slip rate. If I go to a 13P prop, I should gain about 200 RPM (put me at 6100) and possibly cut back on some of that slip. Am I figuring it right?

 

[Sea Rider]

Before venturing playing safely with prop pitches, which type, length of boat is it, how loaded was the combo when achieved 5900 wot rpm range, was the motor trimmed to 90º (fully vertical) with correct deck load distribution running on flat, calm water cond ?

Happy Boating

 

[Geezer1]

Well, I put the 13P prop on and attained 6100 RPM and 30 MPH. That computes to 13.31% slip. Not too shabby for an aluminum prop. I'm happy with it.

 

[Geezer1]

Before venturing playing safely with prop pitches, which type, length of boat is it, how loaded was the combo when achieved 5900 wot rpm range, was the motor trimmed to 90º (fully vertical) with correct deck load distribution running on flat, calm water cond ?

Happy Boating

Sea Rider I appreciate your input. But I have to say that if all of that is your criteria for propping a boat, I believe you're over thinking it.

 

[Sea Rider]

But I have to say that if all of that is your criteria for propping a boat, I believe you're over thinking it.

Sorry, it's not my personal criteria, is what Tohatsu Mortors states/recommends on their Owner's manuals and works best for their motors. Boat size and load are serious wot rpm killers specially with portable motors. To have gained just +200 wot revs going one pitch down you have either a large boat, a heavier load or a combo of both situations.

Happy Boating