Applications of a Non Conventional More Efficient Tip Bladed CLT Propeller
on Bulk Carriers and Judgement Traps of its Performance.
The paper introduces into the historical development of ship propellers. Further concentrating on the envolvement of non conventional propellers with barrier, plates at the propeller blade tips specifically these successfully developed by a Spanish Company SISTEMAR.
In the second part of the paper an account is given on the measurement accuracy of ship propulsive power and propeller efficiency when serious errors may be committed and shipowners may fall into traps of not having the objective picture of their propulsive system.
Key Words: Non conventional propellers of CLT type, propeller efficiency measurements
The history of ship's driving force development simply called a propeller is as old as the history of ship's development itself. The oldest propeller is the oar which before it has reached today's shape has gone through several phases of development. Thousand years before our era in the acient Egypt, Assyria and Babylon ships were propelled by oars, the number of oars on ships sailing across rivers and seas was sometimes reaching few hundreds pairs, and the speed of oar driven ships could be 7 - 8 knots. At the same time of oars application wind force started to be used for ships propulsion as well. Gradually the oars were replaced by sails. After the defeat of the Spanish Armada in 1588 oar or oar - sails driven ships were not any more operated.
The sailing vessels era was on the turn of the 18th century reaching its culminating point, with very large sails they could sail with speeds exceeding 20 knots. The era of sailing vessels ended in the second half of the 19th century when the sailing vessels have been replaced by vessels with a mechanical propulsion.
On the first ships with a mechanical propulsion the propeller was in the form of a paddle wheel. In 1736 year an Englishman J. Hull patented a ship propulsion in which he applied paddle wheels placed at the ship's stern.
In 1807 year Robert Fulton built in America a steamer with paddle wheels mounted at the ship's sides. The first paddle wheels had fixed paddles. In 1829 year Morgan invented a wheel with feathering paddles what has allowed to reduce the paddle wheels diameter by half. Paddle wheels have been widely applied until 1850. A number of paddle wheels short-comings when applied to sea - going ships have caused that they have been supplemented by propellers of a screw type. The idea of using a screw type propeller was due to Bernoulli invention who in 1752 patented a propeller consisting of several blades fixed in a hub. Several inventors have later proposed various propeller designs.
In 1845 a first sea going steamer "Great Britain" with a propeller drive was built. Since than a rapid development of propellers took place leading to total disappearance of paddle wheels application in ships propulsion. The development of propellers in the last century until these days concentrated mainly on optimazation of the propeller blades geometry with the aim to achieve the highest possible efficiency.
Among various geometrical shapes of propeller blades tried by designer and inventors in the past were also proposals of propeller blades fitted with tip plates which should improve the efficiency of the propeller.
2. CONTRACTED AND LOADED TIP PROPELLERS (CLT PROPELLERS)
The first ideas concerning the potential advantages of tip loaded propellers were published in Spain in "Ingenieria Naval" in October 1976 in which a note was made mentioning Tagart's precedent paper published in the "Naval Engineers Journal" (April 1974) in which the concept of placing end plates blade tips in such a way that the blade radius at the leading edge was larger than the corresponding radius at the trailing edge was claimed.
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