Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63H—MARINE PROPULSION OR STEERING
  • B63H1/00—Propulsive elements directly acting on water
  • B63H1/02—Propulsive elements directly acting on water of rotary type
  • B63H1/12—Propulsive elements directly acting on water of rotary type with rotation axis substantially in propulsive direction
  • B63H1/14—Propellers
  • B63H1/20—Hubs; Blade connections
  • B63H1/22—Hubs; Blade connections the blades being foldable
  • B63H1/24—Hubs; Blade connections the blades being foldable automatically foldable or unfoldable

Definitions

• the present invention relates to a foldable propeller for a boat, comprising a hub for fitting to a driveshaft of the boat and at least two propeller blades pivotably arranged about a spindle of the hub between a substantially folded first position and a substantially deployed second position according to the preamble of the subsequent claim 1.
• Such a propeller is usually adapted to being usable together with an engine to propel the boat forwards or rearwards.
• propellers are made foldable, i.e. with propeller blades fastened to a hub pivotably so that they can be folded together (by the boat's movement through the water) in the direction defined by the propeller's driveshaft, to a position in which they extend in the longitudinal direction of the boat.
• the blades are deployed by centrifugal force due to rotation of the driveshaft.
• propeller blades are normally designed to constitute a streamlined body, thereby reducing drag resistance.
• WO 93/01972 refers to a propeller comprising at least three blades which are arranged to pivot between a deployed position and a folded position.
• propellers with blades which can be folded together usually result in little drag resistance, but the propulsive action of these known propellers is relatively poor when travelling forwards and, above all, when travelling rearwards.
• a particular problem of previously known foldable propellers concerns propulsion power when travelling rearwards.
• High propulsion power rearwards when the boat is moving forwards, e.g. when decelerating close to a landing, is usually achieved by increasing the weight at the blade tips and thereby increasing the centrifugal force which causes the blades to pivot about their pivot spindle. The angle of opening of the blades is thus increased.
• increasing the weight at the blade tips entails problems either in the form of thick blade portions with bad cavitation characteristics, or in the form of long blade portions which tend to reduce propeller efficiency, particularly at increased boat velocity, when the propeller is acting in the forward direction.
• a further problem of known foldable propellers is the relatively large forces which occur when propeller blades deployed by the propeller being caused to rotate reach their limit-position stop, resulting in undesirable noise and a "power shock" which is transmitted via the driveshaft and the engine to the hull.
• a general problem of propellers is achieving both high propulsive force and high propeller efficiency when travelling forwards at any desired velocity.
• the general solution to this problem is large propeller diameter combined with low driveshaft speed.
• the propeller's radial load distribution needs to be optimum and the blade area large enough to prevent cavitation.
• the blades need to have thin bent sections of the aerofoil type. Providing foldable propellers with thin blades is a particular problem in that doing so often conflicts with the need for the blades to be heavy enough to ensure that they will always deploy.
• the object of the present invention is to provide a foldable propeller which solves the problems mentioned above. This object is achieved with a foldable propeller according to the present invention, whose characteristics are defined in the subsequent claim 1.
• the invention thus relates to a foldable propeller for a boat, comprising a hub for fitting to a driveshaft of the boat and at least two propeller blades pivotably arranged about a spindle of the hub between a substantially folded first position and a substantially deployed second position.
• the propeller is distinguished particularly by:
• propeller blades take the form of a first and a second blade element, each of which elements comprises blade segments on opposite sides of said spindle, and by
• the blade segments of each blade element are provided with different blade shapes on opposite sides of said spindle. More precisely, the blade shape of one blade segment, the main blade segment, is designed to cause greater drag resistance than the second blade segment, the secondary blade segment. The result is that the propeller folds together when it is not rotating and the boat is moving through the water, e.g. during sailing.
• said greater drag resistance of the main blade segment is achieved by the latter' s blade area being so disposed as to cause more resistance than the blade area of the secondary blade segment. More precisely, the main blade segment is provided with a larger blade width at a radius (r) from said spindle than the secondary blade segment at the same radius (r).
• the hub is provided with a recess for accommodating two of the secondary blade segments of the blade elements when the propeller is in its folded position.
• the propeller thus meets the requirement of relatively low drag resistance when it is not being used for powering the boat, i.e. when it is not rotating.
• said recess is provided by the hub being fork-shaped with two parallel fork limbs extending in the longitudinal direction of the hub, whereby said recess takes the form of an aperture running through between the fork limbs.
• a limit-position stop against which the respective blade element abuts when the propeller is in its deployed position is provided on the inside of each of the fork limbs, i.e. in said recess. This enables accurate mutual positioning of the blade elements, thereby ensuring that an optimum propeller blade profile is always achieved.
• Figure 1 shows a sideview of the propeller in its deployed position according to the present invention
• Figure 2 shows the propeller as seen from directly behind in its deployed position with the propeller rotating and operating in the forward direction
• Figure 3 shows the propeller as seen from directly behind in its deployed position with the propeller rotating and operating in the reverse direction
• Figure 4 shows the propeller in a position halfway between its folded and deployed positions
• Figure 5 shows a sideview of the propeller in ks folded position.
• ref. 1 denotes generally a propeller with a hub 2 for fitting to a driveshaft 3 of a boat (not shown).
• the propeller 1 in its deployed position has two substantially identical propeller blades 4, 5.
• the propeller blades 4, 5 take the form of a first blade element 6 and a second blade element 7, each of which elements comprises, on opposite sides of a spindle 8, blade segments 9, 10, 11, 12 whereby a blade segment 9, 10 from one blade element 6 and a blade segment 11, 12 from a second blade element 7 together constitute a propeller blade 4, 5 in the deployed position.
• Each blade element 6, 7 is made of, for example, bronze, aluminium bronze (containing 8-10% aluminium), steel or a plastic fibre composite.
• the hub 2 may be made of similar material.
• each of the blade elements 6, 7 is fastened, pivotably about said spindle 8, to the hub 2, said spindle 8 extending through cooperating holes 13 in the hub 2
• the blade segments 9, 10, 11, 12 of a blade element 6, 7 are provided with different blade shapes on opposite sides of the spindle 8. More precisely, the blade shape of one blade segment 10, 11, the main blade segment, is designed to cause greater drag resistance than the second blade element 9, 12, the secondary blade segment. The result, when the propeller is not rotating and the boat is moving through the water, is a greater turning moment of the main blade segment 10, 11 about the spindle 8 than of the secondary blade segment 9, 12, thereby leading to the main blade segment 10, 11 being folded rearwards, i.e. folding together of the propeller 1, e.g. during sailing.
• the blade area of the main blade segment 10, 11 is larger than the blade area of the secondary blade segment 9, 12 since the main blade segment 10, 11 is provided with a larger blade width at a radius (r) from said spindle than the secondary blade segment at the same radius (r).
• the blade width of the secondary blade segment 9, 12 is about 0.3 to 0.4 times the blade width of the main blade segment 10, 11 at a radius (r), and a blade width 0.35 times the blade width of the main blade segment 10, 11 is particularly preferred.
• the area of the main blade segment 10, 11 is 70-130% larger than the blade area of the secondary blade segment 9, 12, and a 90-110% relationship is particularly advantageous.
• the two blade elements 6, 7 are identical, making it possible to simplify manufacturing and hence be able to ensure relatively low production costs.
• the pressure centre 20, 21 shifts to a distance which corresponds to about one-third of the total deployed width of the propeller blade from the new front edge 15, 16.
• the fact that the secondary blade segment 9, 12 is so designed that the pressure centre 20, 21 is situated on it results in the turning moment on the blade element 6, 7 about the spindle 8 being greater from the secondary blade segment 9, 12 than from the main blade segment 10, 11, thereby, in a manner similar to that described above, causing the blade element 6, 7 to abut against the limit-position stop 22.
• Figure 5 depicts the propeller 1 in its folded position, i.e. with the blade elements 6, 7 substantially parallel with the longitudinal direction of the hub 2 and thereby constituting a streamlined body with low drag resistance.
• the propeller may be provided with four propeller blades.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• Ocean & Marine Engineering (AREA)
• Other Liquid Machine Or Engine Such As Wave Power Use (AREA)
• Motor Power Transmission Devices (AREA)
• Structures Of Non-Positive Displacement Pumps (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 2004
  • 2004-06-24 SE SE0401652A patent/SE0401652L/xx not_active IP Right Cessation
• 2005
  • 2005-06-14 EP EP05752541A patent/EP1768892A1/de not_active Withdrawn
  • 2005-06-14 WO PCT/SE2005/000918 patent/WO2006001747A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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