Yamaha F70 wants a different prop.

[Durango318]

I'd like some prop suggestions.
I just re-powered my boat after a guy totaled my Merc 60 engine by rear ending it on the freeway. Luckily the transom and trailer were OK. Dang tough boat.
The new engine is a 2016 Yamaha F70 mated to a 2006 Lund 1660 Classic Sport (16' 3") 900 lbs.
The data:
Full tank, one 240lb person, lightly geared, anchor in bow storage.
Prop Yamaha (OEM) White Aluminum 13 5/8 X 14"
Cavitation plate. Aprox 1/4" below bottom (at even trim) Engine mount hole #2 from top, second lowest position.
RPM 6100 at full down trim.
RPM 6300 Trim 20% from bottom (three bars on gauge). Cavitation plate down aprox 2 degrees. Hull was not lifting (flying) but boat jumps on plane.
34.4 MPH two way GPS average. Could not raise trim more because the engine RPM would go too high. (5800 to 6300 WOT rated)

I was considering raising the engine one hole and going to a Turbo FX4 or Turbo Quest 13 1/8 X 16 stainless 3 or 4 blade.
These props have ventilating holes for hole shot with a high pitch.
What do you guys think?

 

[SkiDad]

your idea sounds reasonable. I'm not sure about those props what they will actually do - my gut is they will have more affect on your RPM than you might think. I would probably stick with a 3 blade. 34 is pretty fast for you setup - nice !

 

[Durango318]

Yup, 34 is a pleasant surprise considering how much wet-ed hull there is. Real happy motor. WAY more power full than the 60 Merc it replaced. It already goes as fast as the old one did with the best prop and trimmed up. The dealer may have hung the new motor a bit too low. Just cant remember where the old one was. I yanked off the old one in a hurry for a hungry salvage buyer. I just hope I don't have to go through a lot of props before real magic happens. I'm thinking there's another 3 or 4 mph to be found.

 

[SkiDad]

powertech props could hook you up with the numbers you gave.

 

[Sea Rider]

Durango,

How's your water experimentation going so far, has OB dialed the sweet transom height match ?

Happy Boating

 

[Sea Rider]

Yam and Tohatsu lower legs loves to work at this ideal lower leg/transom height :



Parameters to have into consideration :

-OB must be 101 % healthy.
-Test combo on flat no wind water cond.
-Distribute deck weight evenly.
-Set trim to 90? beforehand or once on plane if at hole shot OB is trimmed in/out
-Have someone pull head out transom and check at which lower leg height is water flow passing at speed.
-If at (O) or X will generate water splashes over/out transom, too much water drag issue.
-Spot on water performance at (1) best prop grip and max thrust.
-So, so at (2)
-Worst at (3) excessive prop aeration on choppy windy water cond an at tight close turns at speed.
-Rise or lower OB accordingly to match (1) or closest to it.

Once correct OB/transom height is dialed, trim can remain at 90?, just distribute deck weight evenly, go full throttle, combo will plane as a breeze.

Before venturing buying some other prop, test actual Yam OEM one as indicated and check max wot rpm achieved. From there can go for a prop maximization for OB to rev to its full 6300 wot revs as currently loaded. Once there will have good hole shot & plane, good top speed along good fuel consumption rate throughout the whole throttle range.

Happy Boating

 

[Durango318]

OK. We tried a Powertech stainless SCD3 13X16 cleaver prop. Drum roll please......... 39 MPH @ 6200 rpm, two way GPS average! The boat was rigged the same as above except a Yamaha 6hp kicker was added to the transom. The hole shot was good, about the same as the stock Yamaha aluminum 13 5/8 X14 semi cleaver. Control and feel were very good. Surprisingly tight u turns without blowing out (at normal trim). Top speed was had with full trim up and the top of the prop was just coming out of the water making a cool sound. Apparently, the prop has little bow lift. The engine mounting was not raised, so the cavitation plate is still about 1/4" below transom at neutral trim. Speed dropped to 38 mph with 240 lb passenger, same RPM. We may raise the engine with other props to be tested.
I'm sad to say the "techs" at Precision Propeller and Powertech were next to useless for prop selection help.

 

[David Young]

The title of 'Tech' is a word loosely used now days . In the 1960's-1970's, 'Tech' meant something or someone special

 

[jrdonicht]

I know this is an old post but I also have a Yamahaf70 with a similar boat as Captain Karl. I am very intrigued the difference that the powertech prop made as compared to the Yamaha 14p{same one he had] which I am now running. Seems like such a big difference. I would like to know more as the prop he choose is not a bow lifting prop therefore more boat in the water?