By Ying Sheng

Surface Piercing Propeller, SPP, refers to the propeller with part of blade above the water and capable of operating normally when the highspeed craft is sailing at design speed. So SPP can be also called partially submerged propeller or surface propeller.Compared with conventional propeller, SPP has many unique advantages. First of all, when the ship which used SPP is sailing at design speed, the hub, shaft, hydraulic support attachments are above the water, so as to reduce added resistance caused by this part of attachments.Furthermore, because SPP is set at the back of the hull transom, thereby avoiding the limitation of the hull on propeller diameter, and then optimizing the choice of propeller working place. When navigating at high speed,compared with SPP, conventional propeller is “fully submerged” in water, the propulsion system of conventional propeller will have to face with the “erosion” phenomenon on propeller surface caused by “cavity”; while using SPP propulsion system can avoid this problem. When SPP is operating, half of blade immerses in the water, the other half above the water. The propeller is always in the condition of “ventilation”, so it will not cause “cavity and erosion”phenomenon. In addition, SPP propulsion system also has high efficiency propulsion, flexible installation, easy maintenance and other characteristics.

Because of these advantages, SPP propulsion system on high-speed craft is used more and more widely.The high-speed planing craft is mainly used in the public service yacht which needs high-speed, such as:customs coastguard vessel, border and coastal patrol vessel, maritime and fishery law enforcement vessel,etc. In addition, high-speed planing craft also has wide application value on military ships. It is understood that SPP propulsion system has been one of the main propulsion modes for the ships with speed over 50kn. On the high-speed planing craft with speed over 100kn, SPP propulsion system has absolute advantages. At present,SPP propulsion system is used widely on the world’s most advanced high-speed planing craft.

The application of SPP propulsion system on high-speed craft has nearly half a century history, but SPP propulsion system is used very little on civilian merchant ships. At present, in the major international classification rules,the research for SPP propulsion system is very little.Because when SPP is operating at high speed, the blade is alternately in the water, the hydrodynamic problem of SPP is too complex, there is no relatively mature SPP map design method now.

In recent years, our country’s marine rights consciousness is improving continuously. Also, marine search and rescue, fi ghting illegal and criminal activities on sea and etc. all require our country to have more advanced, high speed and quick high-speed vessels. This also gives a great opportunity for the research and application of SPP propeller propulsion system in our country.