You are correct, I was in error.

I may have to printoff marylandmark's description. His explination is much better than my notes.

something doesnt sound right,,,if you are spining props out,,you toe out,,right????

Very good explanation, but I think these two points are in error and I changed them to what IMO is correct. Props spinning out means, if looking from the rear, the starboard prop is turning clockwise and port prop turning counter clockwise. So spinning out pushes the props apart and spinning in pulls them together.

i agree with you,,

I called Fountain about this subject once and they said set them "dead straight"

start with calling Hallett, they have done a lot of experimenting on their twins, especially with the 270T...

Thanks, will do.

Short answer is yes.

Long answer is as a V hull moves, the water is displaced by the hull. As soon as the hull has passes, but before the drive or prop passes, the displaced water tries to fill the void created by the hull. That being said, being toed in provides a more natural path of water flow. Water has a lot of pressure, the less resistance your boat/drives/prop gives it the better. The deeper the water is, the more pressure it has. So the water coming up from the bottom of your hull passing has more pressure than coming from the sides. Water against water is a lot of pressure, water against air; air loses. So long answer short is slightly toed in is better than being dead straight. That is regardless if your props spin in or out. In theory, when spinning in, since the water is being funneled that way to fill the void, you may be able to get away with a slightly larger prop. That is in theory and just to help clarify.

Read all of this as if you have to error on one side, when spinning out, error on the side of toed in than toed out.

Incorrect. If props spinning out and you are toed out, you will be more toed out. Less so if you have strong steering, tie bars, etc but that is the way the pressure is pushing none the less.

Every force has an equal and opposite counter force. Look at the back of a boat with the props spinning out. The blade area you see, let's call that the outside blade. That is the part of the prop that is pushing the water, the pressure is there. The inside of that same blade will have a neutral or negative pressure, it is just following the outside blade that is doing all of the work if that makes better sense.

Now think about if those props didn't have any pitch to them, they are just 90 degrees from the hub, blades straight up and down. If one were to spin a prop like that, the water would be pushed directly to the side and for sake of conversation your boat wouldn't move forward. Props spinning out (clockwise), your view point is from the rear, means the water would be pushed to your right. The water is providing resistance in the opposite direction.

Fill up your hot tub, move your hand forward underwater like giving a High Five. Now push your hand forward faster, resistance increases. You are pushing forward, the water isn't exactly trying to push you backwards but provides resistance to your hand going forward. The quicker you try to push your hand forward, the more the water pushes back. Your palm would be the outside blade and your fingernails would be the tip of the inside blade if that explains it better. Your palm has all the pressure on it.

Now back to boats, when spinning out, the resistance of the water pushes the drive towards the center. The water is pushing against the prop but the prop has more force so the prop overcomes the resistance of the water which pushes the water out of the way. Exactly where water just was, the prop now is. It is that resistance from the water that is pushing against your prop shaft. It is that pushing back that makes your toed out become more toed out.

Think of it like this. Stand next to your drive with your right shoulder on your transom, your left shoulder facing away from the boat, your body is lined up with the length of your hull and you are looking directly at your drive from the starboard side toward the port side. Grab your nose cone with your right hand, your prop shaft with your left hand. Pull the nose cone toward you with your right hand, push your prop shaft away with your left hand. That is exactly what the water is doing. So the front (nose cone) that was toed out is now being pulled toward you and the back (prop shaft) is being pushed in. So if you were toed out, now you toed out even more.

Best thing about all of this? When you grope chicks in a hot tub you can tell them you are working on hydrodynamics...

Spinning out pulls them together and spinning in pushes them apart. Remember, we are talking props but toe is in reference to the drives so even a little movement at the prop shaft will have some effect on the nose cone (less with strong steering, etc).

Interesting explanation re. toe in/out, but I'm with 4mulafastech and twin-spins when they disagree with your point above.

When props spin out, the water is pushed towards the center of the boat, not the other way round. At least, there's MORE water pushed towards the center. Therefore the drives are pushed away from the center.

The point you're missing with your explanation is that when a prop spins - theorically - it pushes water around for its whole 360° rotation.
So, it wouldn't make sense to say that the drive is pushed to the right or to the left, because the upper half of the prop pushes in one direction and the lower half in the opposite.
But as a matter of fact, it's the lower half which (for a number of reasons) "grabs" more water, hence encountering more resistance. And with props spinning out, the lower half pushes the drive away from the keel.
That's very obvious if you think of surface props, which in the upper half spin in the air with almost no resistance at all, but even with "normal" X-dim outdrives there's still a difference.
Which btw is the reason behind another effect, the "prop walk", which makes it much easier to turn to port with a single R/H prop and viceversa.

Yes, you all are correct. Sorry!!

I had my perspectives mixed up, typing from one perspective and thinking from another. It's been a long Winter!!!

Opppssss!!!

I have outboards so this stuff REALLY matters. They are toed in and props spinning out so when I was on plane they were toed even further in, causing all kinds of issues.

Disregard or flip what I said above except the part about testing hydrodynamics in hot tubs!!

Teague on Tech: http://www.powerboatmag.com/question...ng-drives.html