I L L U S I O N
42
Tunnel tuning tools
Drive: Depth
- Lower to loosen the boat, higher to wet the boat. Imagine that the prop wants to always
ride at the same depth in the water. If you lower the prop, you are lifting the boat out of the
water. The reverse is true for raising the prop; it lowers the boat in the water.
Drive: Angle
- Negative to push the bow down, positive to push the stern down.
This is a course ride angle adjustment. Small changes in the prop angle make large changes
in ride attitude.
CG:
This is the longitudinal (fore and aft) balance of the hull. Tunnels are usually 24-28 percent
of the hull length, from the transom. This is the pivot point for turning. A forward CG
keeps the hull wetter, preventing blowovers. Limits absolute top speed due to drag.
An aft CG keeps the hull out of the water, and usually blows over with very high speed.
That’s why they call it a “balance” point…
Prop:
The prop is very important to speed, as well as overall handling of the boat.
You can (and should) experiment with many props, lifting and non lifting, to get the best
speed and handling from your boat. Always sharpen and balance your props! A sharp prop
helps reduce “prop walk”, and a balanced one usually stays together!
.
The goal is usually to get as much of the hull out of the water as possible,
without blowing over. This is a compromise. Add the requirement to turn, and
everything gets even more complicated.
Don’t be afraid to try anything, as far as prop or setup.
