x-dim - Improper Lingo?
 

Ok, from what I understand, X-dimension is the vertical distance between the centerline of the propshaft and the centerline of the carnkshaft? Correct?

So if this is the case, without knowing how high the engine is in the boat, saying "my X-dim is 18 inches" tells us absolutely nothing. True?? Saying "I have a high X-dim" makes absolutely no sense as well.

For instance, I'm doing some transome repair this fall and may raise the engine and drive 2 inches in the boat. My X-dim won't change, but my prop will be 2 in closer to the surface.

If the above is true and you're really trying to compare how deep the prop is in the water, wouldn't we want to settle on some term that represents the distance from the bottom of the hull to the propshaft?

I bring this up because I keep seeing X-dim brought up in conversations where x-dim does not seem to be relavent.

Asfar as i know X-DIM. is the hight of the propshaft compared to the botom of the hull.
Because otherwise i does not make sence.
Also ,do not move the engines higher in the boat because u will change your CG (center of gravity) on the boat .
U always whant to keep the engines as low as posible.

BUT , thats just my 2 cents. :party-smiley-004:

X Dimension
 

X dimension is the distance from the bottom of the boat to the center of the drive input shaft. In the case of a bravo if your centerline was 18" above the bottom your x dimension would be 18. In this example the propshaft would 3"15/16" below the bottom of the boat.
Steve

OK, that makes a little more sense, but it sounds like it still isn't the term that most people seem to think it is (as evidenced by post #2). However, as long as the distance from driveshaft to propshaft stays the same increasing the x-dim raises the drive. But that assumes the same drive is used boat to boat (no shorty lowers, etc.). So saying "my x-dim is 18inches" doesn't tell us anything until we know the drive configuration used?

In a couple of posts I've seen people use the term to directly indicate drive height and I swear in one instance the discussion went on and on assuming a numerically larger x-dim means a deeper prop (it's the opposite)

A term for the distance from the propshaft to the bottom of the boat would be more usefull, since obviously the distance between propshaft and driveshaft does change depending on the drive config.

thanks

X-dimension (bottom to crank centreline) measurement is used for cutting the transom.
Higher X = higher prop shaft height. The distance between the prop shaft and crank centre line differs between drives.
Like Smiklos stated 18" X on a B1 will give you a prop shaft height of about 4" give or take depending on the transom angle.

And,
Shorty lower units and/or spacers do not change your X dimension. They DO change your prop depth (- or +). In your case it would be easier to test some shortys and props, than recut your transom. A lower CG does result in better handling, and depending on your engine configuration, you may run out of vertical space beneath your engine hatch.
Regards,
Steve

Ok, here goes!X Dimension: The term "X" relates back to right angle triginometry, the hypotenuse of a right angle triangle is sometimes referred to as X in the equations. On a boat it is the distance "on the transom" from the bottom of the boat to crankshaft centerline. On an X dimension chart, you determine where you want the propshaft (or in some cases the anti-cav plate) relative to the bottom, and you input the transom angle relative to the bottom, the chart tells you what the "X" dimension is on the transom of the boat to mount the drill fixture. The right angle of the triangle is the vertical dimension (what propshaft position you want) and the level bottom of the boat. The hypotenuse (X) is the measurement on the angled transom. Wow! I really can use some of that math I learned in high school!

A good thing i never been in shcool,.......this is getting real confuising !!!!!!

I just put the prop as high as i can and if it dont run ,,,,,,,,,they make spacers to play with !

Dial the boat in get the CG right and run the **** out of it.

ISN'T THAT MORE SIMPLE ?! :drink:

Didn't mean to turn this into a discusion of my project. Was only using it as an example of the confusion I was seeing in posts.

I've already added a 2in shorty and picked up 5mph. Propshaft is still 6.25 inches below the hull. Engine also sits WAYYYY low in the hull. Got about 6-8 inches between the aircleaner and the hatch. In fact the engine sits so low that my tailpipes are almost underwater off plane.

Figure I can probably raise the engine a couple inches and still end up lower than the engine height in most boats this size. Would like to find a used extension box, but that also requires raising the engine.

It would appear your hole is cut for a 15.5" X dimension and the shorty is making it net out to a 17.5" X dimension. If you go much more than 18.5" you may start to have problems depending on weight prop type etc.
Steve

X=Location of crank shaft center (CC) from lower edge of boat bottom.

Yeah it is confusing. I misused "x" a number of times.
Now I say "prop to pad" or "propshaft to bottom of boat" etc. when talking shorties etc.

Raising or lowering the engine a couple of inches in the boat should not change handling AT ALL. Moving the engine forward or backward can have a huge impact on handling.

IMO, not worth the $$$ invested at all. You may not gain another mph and might have to spacer it back down. 6.25 is deep, but not extreme. Plenty of straight V's run that deep. Being deep gives leverage and bow lift.

Thanks. Saw a couple of threads on smaller V hulls like mine where people were talking 2.5in or 3.5in, with 2.5 being too shallow. I haven't seen anywhere where anyone went up from over 6 inches and regreted it. Although, I think I am going to leave it where it is this year. First I've got some bottom work to do this fall, including removal of some wedges, and minor straightening. We'll see what that does for me, then look into rasing the drive with an extension box next winter.

One thing to remember is that I consider this boat to be one big experiment. I'm trying to learn all I can and experiment as much as possible (and do all the work myself). Yeah, I've put a lot of effort into a $20K boat, but hopefully I'll learn enough not to ruin a $200K boat in the future. Yeah, I've made a couple mistakes, and spent a lot of my time, but slowely but surely this boat is inching up on "fast" territory and I'll come out a lot more educated.