Tohatsu 70A2 prop choice

[kaferhaus]

I'm going to move this engine from a 17ft CC to a 14ft CC so it's going to need re-propped.

Closest educated guess I can come up with is a 17 pitch prop...which still may be a bit under... as this is a very light boat

The boat is a 1987 14' Mckee Craft with a dry weight of 665lbs, 120lbs fuel, 110lbs gear and two persons.

The boat IS rated for 70HP.

I've tried the various "prop calculators" that I could find and most won't even return a result....one came back with a 22 pitch!!!

Is this 17P a reasonable starting point?

 

[steelespike]

Re: Tohatsu 70A2 prop choice

Run it with your present prop get your max rpm and speed and make your decision from there.Prop selection would depend partly on your present max rpm and speed.
w the 17ft.
I wouldn't make any changes without the specs with original prop on the new setup.

 

[kaferhaus]

Re: Tohatsu 70A2 prop choice

Run it with your present prop get your max rpm and speed and make your decision from there.Prop selection would depend partly on your present max rpm and speed.
w the 17ft.
I wouldn't make any changes without the specs with original prop on the new setup.

I understand how to figue the prop needed when you know what you have... that's pretty much childs play.....run it wot with your normal load in the boat add or subtract 1 step in pitch for every 400 rpm outside the engine's WOT range.

The problem is the current prop is an unknown. No markings on it other than a casting mark. No numbers on the prop anywhere.

Any "layman" way to measure the pitch?

 

[TOHATSU GURU]

Re: Tohatsu 70A2 prop choice

Figure on a 19 pitch prop being about right on that application. A 17 would be right if you were doing some water skiing. The easiest way to determine prop pitch is to run your old one by a prop shop and let them measure it.

 

[kaferhaus]

Re: Tohatsu 70A2 prop choice

Figure on a 19 pitch prop being about right on that application. A 17 would be right if you were doing some water skiing. The easiest way to determine prop pitch is to run your old one by a prop shop and let them measure it.

Thanks Elvin.... I was thinking my "guess" at 17 might yet be a little underpropped... I hadn't thought of going by the repair place... there is a shop in town that repairs props...

Finding a 19P prop to fit it might be a interesting exercise....LOL

Although I'm no speed freak by any means... I'd imagine that little Mckee is gonna fly at WOT... but maybe it'll let me cruise at 35 without killing me on gas.

 

[TOHATSU GURU]

Re: Tohatsu 70A2 prop choice

Rewind the 19 pitch...It didn't register that you had an A model. A 17 is actually a hair high on that one. You might want to start off with a 15 pitch. That model uses a very small diameter prop.