Why Surface Piercing Propulsion?
Surface Drive Comparison to other propulsion systems
The specialized “Surface Drive” propeller operates half in and half out of the water in the “cut water” or “planing wake” region that occurs immediately behind a boats transom when planing. This is due to the propeller shafts flat, almost horizontal exiting through the boats transom, not the bottom, as conventional 12º – 18º inclined shaft, inboard powered boats do.
to conventional wisdom, the incline of the traditional inboards
propeller shaft causes it’s propeller to have an angle of attack such
that, the majority of thrust is produced with the lower blades during
the propellers rotation. Therefore throughout the top half of its
rotation the blades only generate minimal thrust, and cause resistance.
Further resistance is created by pushing through the water the propeller
shaft, its support strut and the entire rudder.
Additionally the top blades receive disturbed water caused by the
spinning shaft and strut ahead of it creating further inefficiencies.
As well inefficiencies occur with the inboards 12º - 18º propeller
shaft angle expending a significant portion of thrust down into the
water. The objective is to simply push the boat horizontally. In the
case of a twin inboard boat, multiply the resistance and inefficiencies
The result for the Surface Drive is an approximate 20% gain in efficiency over inboards due to the improved thrust angle and the eliminated resistance of the underwater appendages. With the Surface Drive, only the thrust producing bottom propeller blades and rudder tip are immersed which also provides the added benefit of reduced draft.
Efficiency of Other Drive Systems
Are basically a water pump and operate on a "Differential of momentum principle" They are inherently less efficient than Surface Drives because:
Out-drives are less efficient that a Surface Drive because:
What About Damage from Floating Debris
Inboards and out-drives are more sensitive to damage from floating debris because:
The bottom line is that a surface drive surpasses the efficiency of any other high speed drive system available. Typically an efficiency gain of 10 - 20% is recognized over Out-drives, Inboards, or Water Jets.