SISTEMAR - CLT PROPELLERS
SISTEMAR is a Spanish company with main objective that of design and commercialization of CLT propellers®, high efficiency propellers with end plates at the blade tips, which improve notoriously the performance of the conventional propellers.
The merits of Tip Plate propellers (higher efficiency, lower noise an vibration levels and better manoeuvrability characteristics) have been demonstrated in more than 350 full scale applications on very different ship types.
In particular the efficiency increase (and hence the achieved fuel saving) allowed for by CLT propellers is in the range of 5 – 8 %, being higher for slow vessels with high block coefficient as tankers, bulkers, etc... making CLT Propellers the most attractive device for increasing the propulsion efficiency and lowering the EEDI and the EEOI.
Notwithstanding CLT Propellers are a mature and reliable design their refinement is still ongoing, as testified by the recent development of the so called New Generation CLT Propellers.
CLT propellers - Theorical fundamentals
The Contracted Loaded Tip propellers (CLT) are screw propellers with important load at the blade tips thanks to the fitting of end plates at the blade tips that actuate as a barrier avoiding the communication of water between both sides of the blades, and the appropiated design of the blade geometry and the radial load distribution. The end plates are positioned so as to cause a minimum viscous resistance and therefore are parallel to the incoming flow and shaped to the relative motion of the water, taking into account the fluid vein contraction.
The tip plate is located on the pressure side of the blade with the aim to obtain a higher overpressure downstream.
The underpressure on the suction side caused by a CLT propeller is much lower than for an equivalent conventional propeller whilst the overpressure on the downstream side is much higher.
CLT propellers – Advantages
Energy saving is a primary objective in the design of marine propellers; the increase of oil price and the more strict regulations in terms of air pollution and NOx/Sox emissions require more and more efficient designs. At the same time, requirements about radiated noise and vibration emissions in order to reduce the negative effects on marine life and the hydroacoustic signature of new commercial and navy vessels are the primary aims of any newbuilding.
CLT propellers represent a further opportunity to increase efficiency, reduce the risk of cavitation (and radiated noise as a consequence) without the employment of completely different geometries and propulsive solutions (ducted, contrarotating, etc.)
CLT propellers, thanks to the higher efficiency, help reducing the fuel consumption, the emissions and then both the Energy Efficiency Design Index (EEDI) and the Energy Efficiency Operational Index (EEOI) without requesting any modification to the vessel.
The main advantages of CLT propellers can be summarised as follows:
HIGHER SHIP SPEED
LOWER FUEL CONSUMPTION
REDUCTION IN CO2 EMISSIONS
BETTER MANOEUVRABILITY CHARACTERISTICS
LOWER NOISE AND VIBRATION LEVELS
LOWER OPTIMUM DIAMETER
MUCH BETTER PERFORMANCE FOR CP BLADES IN OFF-DESIGN
HIGHER CAVITATION INCEPTION SPEED
HIGHER KT MARGIN AGAINST FACE CAVITATION
The underpressure on the suction side caused by a CLT propeller is much lower than for an equivalent conventional propeller, while the overpressure on the downstream side is much higher.