two-air

I am confused.. What is faster.. A high-X or low-X.. I have just learned that a spacer which lowers the X-dimension makes the propeller more efficient reducing slip which increases speed.. I was always under the impression that a high X was the way to go??

What is the relationship??

hillbilly24

there are alot of factors that come in to play with this. The boat has to be propped for the x dimension some props work better burried deep and some run better toward the top. spacers are ussualy ony used with shorty lowers to achieve the optimom drive depth. In an I/O boat by installing a shorty or a spacer you are not truely changing the x dimension, you are changing prop depth. The x dimension is the distance from crankshaft centerline to hull bottom on an I/O. On an outboard it is prop shaft centerline to the bottom of the boat. Generally speeking a higher x dimension is faster but looser but not always. As I said there are ALOT of other factors that have to be considered before decideing wich is faster on a certain boat. The saftey are control factors also have to be weighed against the speed increase. Even if it will pick up 3-5 MPH it may not be worth it when you consider the safety of you and your passangers. Most boat builders set em up with a drive depth that isn't redicoulosly deep but they do air on the side of safety in most cases.