How to measure X-Dimension and hull degree ?
 

These terms are used alot and Im curious as to how they are properly measured.

A quicky way to mesure the x is to measure from the bottom of the V to the bottom of the gimble. Then add 9.25". That'll get you in the ballpark.

Does that equation apply to all outdrives? Mines an OMC. I guess I want to know what the definition of X dimension is as well as how to calculate it.

The X dimension is from the bottom of the v to the centerline of crankshaft

Or you can simply measure the distance from the centerline of your prop shaft to the bottom of your V. Mine is 4.5 inches (shaft below the V). A lot of guys use this dimension to compare boats. As for hull degrees, you would really need and inclinometer to correctly measure it. Or you can do the geometry thing and figure out how far it falls per inch. Then do the math (and DON'T ask me to do it!!!!) I have a digital inclinometer at work, so I don't have to do no stinkin math!!!!

Ok, one says centerline of crankshaft to bottom of vee, the other says centerline of propshaft. Judging from the 59 views with only a couple responses, looks like I had a question worth asking. Back to hull degree. Measured at the transome I'm guessing?

Mercury measures their x-dim from the bottom of hull to the crank center line. It's roughly 9.25" from the bottom of the bravo/alpha gimble to the center line. So no, this won't work for your OMC drive.

What WF is talking about is the same thing. The higher the x-dim is the more the drive comes out of the water. It's really the distance below the bottom of the hull that matters. For example-if you had a 15" x-dim and put a shortened lower unit out, your x-dim wouldn't change even though the bottom to prop shaft distance was reduced. Does that make sense?

What should the x dimension be on a 27' single engine boat with a 24 degree dead rise be. I know it varies with different boats, but approximately how far down should the center of the propsahft be the bottom ov the V?

Im at 8-9 inches roughly with my King Cobra on a 26' Liberator. Is that alot? Just purchased a Rev4 as I am told they are good for deep x-dimensoin setups (thats why I asked this question). My slip is at about 17 % with every three blade Ive tried. Hoping this workes .

It depends on what your use is. Theres a bruiser by my dealer that has the gimble mounted right on the keel. The prop is what 10", 12" below? There's a P-29 Scarab up here where the prop is at least 1" above the bottom. Neither height is wrong as their purpose is different.


But to answer your question: your boat is setup to be a cruiser and will never see a very high efficency or speeds. The prop is too deep for a high speed boat. The trade off is that you'll have good low speed control, a effective reverse, and be able to tow a dozen skiers. Short of actually filling the transom to raise the gimble/engine I know of no way to raise your x-dim.

Im not convinced, prolly cause thats not what I want to hear. My boat runs right about where it should for its size, weight, and power. My big problem is getting positive trim. I would think that with a deeper prop, more actual trim (like what is shown on the trim guage) would be required to lift the nose. Kind of like using a longer breaker bar on a nut. You can apply more force but have to move the wrench further. I think that the reverse of this is limiting the amount of trim I can get. The force applied to the prop by the weight of the bow is increased becuase of the length of the outdrive below the hull. The prop cant hold the bow up and blows out. Im hoping that the four blade will hold the water better resulting in the ability to increase positive trim. I just purchased the prop from a member here and will know as soon as it arrives.

If you need large amounts of trim to carry the bow of your boat, then the rev is a prop that you could try but I wouldn't buy it. You'll need a higher rake prop than the rev. The machs arn't the best props on the planet, but I'd be trying the sterndriver.

I heard/read that the 'X' dimension is the distance from a horizontal line up from the V which measures the width of the cavitation plate or about 5"- from that line to the crank centerline.

That is draw and move a horizontal line up from the point of the V on the transom until the line is 5" wide and then measure from there.

Same question and so many answers. What is 'X' dimension? Too many definitions and confusing.

I like a better measurement of propshaft location in inches above or below the 'V' point or for cats the bottom of the sponsons.

I too have heard of that method...guess it depends on who you are talking to as to whether it's correct or not.

Well, time to test my memory again. According to what I remember from the Merc layout templates, the X dimension according to Merc is the distance from the crank centerline to where a vertical line through the crank center intersects the bottom, measured on the transom surface. On a single this would be the bottom of the V, on a twin this would look like a rectangle when drawn on the transom.

As boat transoms are usually built at an angle of 10-14 degrees from vertical, the length of a line drawn on the transom (X spec) will change with transom angles to produce the same crank/bottom distance.

As the prop / crank distance various on the different drives, so does the recommended X.

The real thing that matters is where the prop is in relation to the bottom, that is what I really look at. As I can barely remember breakfast at lunchtime, I don't even try to remember the X spec for the different drives. I just want to know where the prop is. It also is very difficult to measure once the engines are in. I scribe a small line at the crank C/L that is visible once the drives are mounted.