Page 67: of Maritime Reporter Magazine (April 1986)

A modern highly skewed KaMeWa controll- able-pitch propeller.

In many cases, considerable fuel savings can be achieved by modify- ing the propeller blades or by re- placing the existing blades with new ones optimized for the new operat- ing conditions. Among alterations that may be considered are the fol- lowing: • Reduction of the propeller di- ameter

This may be considered for geared medium-speed machinery where the number of engines uti- lized per shaft has been reduced, where one engine per shaft is used instead of two, two instead of three, etc. • Increased propeller diame- ter

An increase in diameter may be considered if the new and reduced power can be utilized at the shaft speed that is reduced more than cor- responding to the cubic root of the power ratio (Pn:i = "propeller law").

This condition may often apply for plants with directly coupled, low- speed diesel engines. To prevent propeller-induced vibration from increasing due to reduced tip clear- ance, blades of the highly skewed type may be considered. • Reduction in blade area and/ or thickness

Such reductions contribute to in- creased propeller efficiency by re- ducing friction between the water and the blades. In most cases where propeller power is reduced, blade area may also be reduced without risk of harmful cavitation. • Changes in radial pitch dis- tribution and/or blade section camber

These alterations may be consid- ered, in combination with some of the changes discussed above, if the original blades are operating with an unfavorable load distribution.

Highly Skewed Blades

For severe propeller-induced vi- brations, propeller blades of the highly skewed type are recom- mended. These blades yield vibra- tion levels that are only 30-50 per- cent of those experienced with con- ventional blade designs.

Since 1978, KaMeWa has deliv- ered some 250 propellers with high- ly skewed blades. Most of these were for newbuildings, but about 20 per- cent were for retrofits—replacing existing blades of conventional de- sign.

The high-skew blades are charac- terized primarily by their low vibra- tion impulses. As a rule, the HS pro- peller will result in vibration levels in the hull only 30-50 percent of the levels occurring with conventional blades. Despite this very low excita- tion level, the HS blades yield pro- peller efficiencies equal to those of conventional propellers.

Because of low vibration im- pulses, accompanied by an im- proved comfort level in ship's ac- commodations, HS propellers are fast becoming standard for all types

Box 10326 Bi

Telephone (20

TWX 810-733-!

Circle 201 on Reader Service Card of passenger ships as well as naval ships where low noise and vibration levels are vital.

In all cases when the old conven- tional propeller blades have been replaced by new HS blades, vibra- tion and noise levels are reduced.

For a copy of the complete report and free literature on KaMeWa pro- pellers,

Circle 93 on Reader Service Card

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April, 1986 71