alter ego

I have read a few things about the x dimension on this forum but I don't know exactly what it means. I know it has to do with the relationship of the outdrive to the boat and there is some optimum distance. Would this affect how well your prop grabs water on plane or expain why some slip more when trimmed up? I was looking at my boat today and it seems like the keel is lower than the cavitation plates on the outdrive. I noticed I have a lot of slip when I trim up even close to neutral. Could it be that my boat is designed that way without an optimum x dimension or is it just that I need a prop with more pitch?

Comanche3Six

[QUOTE=alter ego]I have read a few things about the x dimension on this forum but I don't know exactly what it means.QUOTE]
Crankshaft centerline

Zanie

[QUOTE=CigaretteFirefox]Or more clearly;
X dimension is the vertical distance from the crankshaft centerline to the running surface directly below the crankshaft. The X dimension is measured at the transom. The distance is measured true vertical (not following the transom surface). So the actual measurement ends up in space, as you have to draw a line extending your ruuning surface and then measure straight down from the crank centerline until the two lines intersect.

When people speak of the X dimension with twins they also mention the distance between the crank centerlines of the two engines.
For instance, the X dimension of my boat is 18.5" X 34.5"

Get it?
Good luck,
Dan

alter ego

I was way off.....I thought it had to do with the outdrive and the distance behind the boat and how deep it allows the prop to go in the water. I thought that was why people put short drives on or extension boxes on to get better speed or handling. What makes the x dimension so important? Is there an optimum measurement between the transom and crankshaft angle?

throttleup

The optimum X dimension is different on every boat, motor, drive and prop set up. There are many factors that determine the optimum drive height and this is determined through testing.

What type of boat do you have? What is the WOT rpm, drive gear ratio and Prop pitch? After determining what the slip is then one can figure out how the current drive height is working and make changes from there.

Matt

Zanie

So in other words, you don't really need to know what your "X" is. What would be helpful to know is what your prop height is: The distance below (or above) the running surface that the centerline of you propshaft is from the running surface. Trim your drive(s) flat (as in parallel to the running surface). lay a flat edge on the running surface directly verticle to the prop and measure the distace (up or down).

Dan.

alter ego

Thanks....Well I can see what the prop height is then. I think my slip is way up. I have a 28 Stryker Equalizer with a 502 mpi. The motor is generating just over 600hp. The rpm for peak horse is about 5600 but peak torque is in the 4800 rpm range. The weight of the boat is listed at 4600lbs but that has to be dry. My drive is a Bravo one with a 1.5/1 ratio and the prop is a 24 pitch accelerater from Houston prop. Darin is going to be working it a little more this winter. The slip has to be up there because at 5200rpm I can't be trimmed up past about 5/8 of the way to nuetral without losing speed. My top end on this prop is 58.8mph on gps. I have a Ballistic 24 pitch that gets 60.4mph but has trouble in rough water. It just can't grab in heavy chop cruising.

offthefront

iTrader: (1)

Alter .. this your boat ?

alter ego

Mike,

Thats the boat you were looking at last year.....I saw a pic of your new boat on the formula section. Great looking boat!!! I'm working with Darin at Houston Prop to get this combination maximized. When I got it the fuel pressure was turned down to 17psi and it needed some attention here and there but running pretty well now. I have some better pictures of it now that the season is through. I am having trouble uploading them but I'm working on it. How are things going with your Formula?

monsta

the higher your x, the more blades or pitch or both you'll need .