Rage

Will someone explain the term 'X'factor as relates to a boat's hull design versus drive location?

KNOT-RIGHT

Let me see:

"X" dimension is the distance "on" the transome from the intersection of the boat bottom and transom ( drive location) to crank center to place the prop shafts at the desired heights.
This "X" dimension ends up being the "measurement" as you have to draw a line extending your running surface and then measure straight down from the crank centerline until the two lines intersect.

Have I Confused you enough yet?

tj309

X dimension does not generally apply to outboard applications because most high perf boats have jack plates which change the X dimension. (X dimension being the vertical distance between the crankshaft centerline and the prop shaft) In a stern drive application the crank shaft is horizontal and therefore measurable. Outboards are vertical so what you are probably really asking is drive height. Depends on how fast you want to go. The high perf rigs will set propshaft centerline about 1 to 1.5" above the bottom of the transom assuming surface capable props etc....

jpclear

Yes, Caveman has it! However, "X-dimension" and "Prop-shaft height" are not the same thing. Julie or Matt at "Throttle-Up" can explain it real well. Give them a call or e-mail them with your specific concerns and I am sure that they can give you answers as it pertains to your situation. --- Jer

Rage

Caveman,

Thanks, I now understand the 'X' dimension.

The 'X' dimension was mentioned in another thread indicating that the 'X' dimension of the Nordic Heat was not what it should for good top end speed. It was noted that this situation could be improved and the top end speed increased by using drive spacers to lower the lower unit/prop shaft position deeper into the water. I think that they were trying to get more bow lift at WOT. Conversely I know that the more of the drive that is in the water the more drag there will be.

Any idea about the merits of this approach?

I am trying to learn more about this factor and if it is something I should try on my Nordic Rage to improve top end.

fastestbowtie

I am glad you do, because I still don't. I thought it was just another fancy term used to describe the distance between the center of the propshaft (when trimmed parallel to the hull) and the lowest point on the hull. Now someone is saying there is more to it than that??? Can someone clarify this.

Kidnova

I'm with you fastbowtie.

Could be wrong on this but, I don't think the angle of the dangle matters ahelluvalot. For most go fasters, I think the prop shaft center line in relation to the bottom of the boat is what matters most.

If there's more to it, and expanation in simple terms would be helpful.

Rage

Now that I am educated on the subject the 'X' factor is essentially the distance between the motor out put/crank shaft and the bottom of the boat hull at the transom BUT since the leg bone is connected to the thigh bone wherever the motor goes so goes the drive. So in effect the 'X' factor INDIRECTLY determines where the drive shaft is relative to the bottom of the boat hull at the transom which is the important issue, not the location of the motors crank shaft axis.

If I still got it wrong then shot me!

Thanks!

jpclear

Yes, you have it 99%. "X" dimension is the distance from crankshaft (or even more correctly, drive input) C/L to prop shaft C/L when trimmed parallel with the extended hull keel line and measured at rt. angle to that keel line. (not along the slanted transom) Prop shaft height (which is the dimension that most prop builders want to know in order to set you up with the right prop) is the distance, again measured at rt. angle, from the extended hull keel line to prop shaft C/L, and again trimmed parallel. It all sounds more complicated than it really is. --- Jer