low_psi

There was a decent article in the May 2013 Performance Boats Magazine in the Teague on Tech section on this very matter. Since I don't have a twin, I honestly don't know if it was good information or not, but a good read....

pstorti

iTrader: (2)

yes it is opposite of what you and Griff are saying. Spinning out is starboard clockwise and port counterclockwise, the bottom half of the prop is what pushes the drive, so a clockwise rotating prop wants to move the rear of the drive right (starboard, out), a counter clockwise rotating prop wants to move the drive left (port, out).

I don't understand how you guys figure it works the other way.

pstorti

iTrader: (2)

the effect is worse because the top half of the prop isn't offering any opposing force. But a surface style drive example just reinforces my point.

pstorti

iTrader: (2)

http://www.performanceboatsmag.com/online-magazine/

POWERPLAY J

Makes sense. I was thinking of the down turning blade pushing the transom up and drive in. BTW P thanks...

scarab600

So what speed and or handling difference being 1/8" off do you think it would make.

offshorexcursion

iTrader: (5)

Reggie fountain wrote on a thread here and Bob Teague wrote in that article quoted in this thread, that the nosecones should be closer together then the prop shafts due to the V Hull Water flow. Neither of them explain what forces the props have on the drives in a submerged (standard bravo style) condition.

Now Bob does explain in the article linked more details on surface drives and cats. Lets not get that confused with a standard bravo style V bottom.

So YES, on a SURFACE drive the bottom half of the prop is what pushes the drive, I have not read anywhere that the same is true WHEN the prop is FULLY submerged??

Still a little confused but learning more and more everyday!

Still going to try different ways on my personal boat, but just like to understand the science behind what I am doing also.

pstorti

iTrader: (2)

The same is true for any prop, the reason the prop pushes the drive has to do with water pressure differences due to depth and differences in water speed due to the effect of the hull, as you get deeper the pressure increases which give the lower half of the prop better bite and allows it to dictate the direction of force, also the water coming off the hull can be moving faster than the water deeper down which. Obviously on a 15" prop it is a very small difference but its enough to cause an effect. on a surface drive the difference is large because the water pressure is zero on the top half of the prop and the hull has no effect on it. Think about how an airplane maneuvers minute differences in air pressure are all that is needed to make a huge jet change direction. Same principles different fluid. If you have ever driven or been on a marina launch the kind used to get boaters to moored boats, or any single screw inboard with a rudder. They will crab sideways in one direction easy as can be in the other direction not so much, the reason is due to the prop rotation and its tendency to walk left or right depending on the rotation. Do a search on prop walk and you will find lots of explanations. The reality is that every boat is different and either trial and error or talking to somebody with experience setting up your hull are the only ways to figure out the best setup.

SRQ

I've read the whole thread. Try this. Take your props off. Measure you're current toe in or toe out measurements. Now take a cinch strap and wrap it around your port and starboard prop shafts and apply some pressure on them. I guarantee you'll see your statics specs fly right out the window and your drive will also go out of parallelism too. Static settings are all depending on the play in the hinge pins, gimble ring and tie bars etc. Trial and error are the only way I know to obtain the best handling and speed for any given setup and propellers.
Just my own personal experience and two cents worth.
SRQ

offshorexcursion

iTrader: (5)

UPDATE!

Tried the Drives toed both ways and could not tell a difference in speed or handling!

No biggie, its fun to learn and try new things.