Prop Rotation
 

Which is which?

Props turning in = Bow Lift or Stern lift

I have heard and read it both ways.

On ours, props turning in is chine walk, props turning out, same speed, better handling.

Doesn't matter on a single. Only offers difference in lift characteristics on a twin.

On a single, it just changes the direction that the boat torques or leans at speed.

I'm asking about a twin setup.

Turning in= bow lift turning Turning out= stern lift

Tyler Crockett said just the opposite in Feb 2004 Hot Boat Stern-Drive Tech column.

don't care what was printed in the column.

On a vee hull, spinning in pulls the rear of the boat down, raising the bow. spinning out raises the rear of the boat, creating stern lift.

I read that article also and wondered if he was having a brain fart or if no one proofreads anything before it goes to print.

That makes since to me. Don't believe everything you read.

ACTUALY JUST THINK ABOUT IT. TURNING IN SHOULD BRING STERN DOWN. HOLD YOUR HANDS IN FRONT OF YOU AND TWIST THEM BOTH INWARDS IT LOOKS LIKE STERN WOULD GO DOWN .NOW TURN THEM OUTWARDS TURN WILL LIFT

Do you look at how the props are rotating in the water on the outside to know if they force upwards or downwards forces on the stern? Seems like on the insides, the wash from both props would give no bite. Because if you look at the direction they rotate, the blade coming out of the water will want to pull the stern down. But while there is a blade coming out, there is another one going in, wanting to lift the stern up. Which has more influence?

On my F311 SR1, turning in wouldnt hold the bow and lifted the stern. I had to turn them out. This was with 3 blade mirages and a higher than stock x-dim. ??

turning the props out always lifts the stern.
Turning them in always gives more bow lift.
Cleaver type props cause stern lift and round ear props give better bow lift.

And, then when you throw 4 blades into the mix??

One blade, ten blades, it's just more blades.

The blade STYLE (cleaver and chopper are the two most popular templates for a prop blade) is the main factor that influences bow or stern lift. Individual blade tweaks can influence these characteristics but to a lesser degree.

Now, there are stern lifting 4 blades and bow lifting 4 blades. Choose your poison.

We could go on to talk about 5 blades, too, but it is the same story.

Setback and X height are setup parameters that affect the choice regarding how many blades you need.

The higher the prop runs out of the water, the less blade area it has in the water at any given time. Less blade area is less load carrying ability. On a light boat it doesn't matter as much. On a heavy boat, a 3 blade may not be able to plane satisfactorily while a 4 blade may give it enough area to move the load.

Also, the more blades you have in a high X application, the less steering torque you must fight (a non issue in a twin but a VERY significant issue in a single).

In a raised X boat.
The closer that you run the prop shaft to the running surface of the water the more it will tend to lift the stern.