(19) & (11) EP 2 371 701 A1 (12) EUROPEAN PATENT APPLICATION (43) Date of publication: (51) Int Cl.: 05.10.2011 Bulletin 2011/40 B63B 35/68 (2006.01) B63B 39/06 (2006.01) (21) Application number: 10157085.1 (22) Date of filing: 19.03.2010 (84) Designated Contracting States: (72) Inventor: De Jong, Jochem Steven AT BE BG CH CY CZ DE DK EE ES FI FR GB GR 3572 NV, Utrecht (NL) HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO SE SI SK SM TR (74) Representative: Uittenbogaart, Gustaaf Adolf Designated Extension States: Indeig B.V. AL BA ME RS Bloemendaalseweg 277A, P.O. Box 3 (71) Applicant: BV Scheepswerf Damen Gorinchem 2050 AA Overveen (NL) 4200AA Gorinchem (NL) (54) Ship such as a tug with azimuting tractor drive (57) The invention concerns a ship such as a tug forming a main active steering equipment, and rearward comprising a hull (2) with a foreship and an aft ship and of the amidships preferably near the aft ship a stationary a length that is less than 3.0 times and preferably less course stabilising skeg (18). than 2.5 times a beam of the hull, located forward of the In accordance with the invention, two rear skegs located amidships two propulsion and steering units (6) with pro- symmetrical on both sides of the hull’s centreline form pellers (7) having approximately horizontal rotation- axes the course stabilising skeg. EP 2 371 701 A1 Printed by Jouve, 75001 PARIS (FR) 1 EP 2 371 701 A1 2 Description and small steering angles. [0009] In accordance with an embodiment, the ship is [0001] The invention concerns a ship such as a tug in according to claim 9. In this way, the struts and the rear accordance with the preamble of claim 1. Such ships are skegs can support the ship during docking. known as azimuting tractor drive tugs and are in use as 5 [0010] Hereafter the invention is explained with the aid stable and easy manoeuvrable platforms for inland, har- of two embodiments of a ship with the aid of a drawing. bour, or offshore towing and ship assistance. The known In the drawing ships have a central course stabilising skeg and the con- Figure 1 shows a side view of a tug according to the prior figuration of the propulsion and steering units and the art, front of the central skeg lead to a course keeping insta- 10 Figure 2 shows a rear view of the tug of figure 1, bility. This instability means difficult and even unpredict- Figure 3 shows a side view of a tug according the inven- able steering behaviour. This is a disadvantage in terms tion, and of safety in ship handling. The cause of this instability is Figure 4 shows a rear view of the tug of figure 3. the interaction of the two propulsion jets generated by [0011] Figures 1 and 2 show a tug 1 according to the the propulsion and steering units located in front of the 15 prior art in water with a waterline 3 according to maximum central skeg. When steering, the direction of the propul- draught. The tug 1 has a hull 8 with a foreship 2 and an sion jet makes an angle with the centre line of the hull aft ship 10 and has a length that is less than 3.0 times and one propulsion jet creates an asymmetrical flow the beam and approximately 1.9 times the beam. Such against the vertical front of the central skeg. This asym- a tug 1 is suitable for use in inland, harbour, or offshore metric flow against the central skeg can generate a steer- 20 towing and ship assistance and offers a stable platform ing torque on the hull that counteracts the steering torque for a crew to work on. On the aft ship 10 there is a bollard generated by the propulsion jets of the propulsion and 12 and a winch 13 and around the aft ship 10 there is a steering units. This leads to unexpected instability. In or- fender 11; these equipments are used for assisting and der to overcome the disadvantage the ship is in accord- towing ships and barges. The tug 1 has a wheelhouse ance with claim 1. It has appeared that the two rear skegs 25 14 and has all necessary equipment for its intended use. keep the ship on course and give the ship predictable [0012] The hull 8 has two propulsion and steering units steering characteristics while free sailing. 6 that are located near the foreship 2 forward of the amid- [0002] In accordance with an embodiment, the ship is ships and extending under the hull 8. There is no rudder according to claim 2. In this way, the skegs do not gen- and there is no other active steering equipment. Each erate sideways forces during vertical movements of the 30 propulsion and steering unit 6 has a propeller 7 that ro- skegs in the water if the skegs move in vertical direction tates around an approximately horizontal propeller axis relative to the water due to movement of the ship or due 5. The propeller 7 also rotates around an approximately to waves. vertical steering axis 4 to change the direction of a pro- [0003] In accordance with an embodiment, the ship is pulsion jet generated by the propeller 7 and so steers the according to claim 3. In this way, the propulsion jet of one 35 tug 1. In addition, for steering the tug 1 the rotational of the propulsion and steering units can flow between the speeds of the propellers 7 can be different so that the rear skegs, which leads to increased predictability of the starboard and port propulsion and steering units 6 gen- steering behaviour caused by the rear skegs. erate different propulsion forces. [0004] In accordance with an embodiment, the ship is [0013] The aft ship 10 is V-shaped; figure 2 schemat- according to claim 4. In this way, while free sailing in a 40 ically shows the section lines 19 indicating this shape. straight line the propulsion jets create a flow on both sides For improving the straight-line stability of the tug 1, the of the rear skegs, which increases the stabilising forces. aft ship 10 has a centre skeg 9 that extends in longitudinal [0005] In accordance with an embodiment, the ship is direction under the centre of the hull 8 to the stern. according to claim 5. In this way, the rear skegs extend [0014] Figures 3 and 4 show an embodiment of the tug sufficient deep in the water so that a lateral movement 45 1 wherein the aft ship 10 does not have one centre skeg of the hull creates lateral resistance on the rear skegs to 9 but has two side skegs 18 that are located symmetri- improve the course keeping stability of the ship. cally to the longitudinal axis of the tug 1. In the shown [0006] In accordance with an embodiment, the ship is embodiment, the side skegs 18 are located at the width according to claim 6. In this way, the full height of the of the vertical steering axis 4 of the propulsion and steer- propulsion jets influences the flow on and/or around the 50 ing unit 6 so that they extend in the propulsion jet gen- rear skegs, and so the course stabilising influence of the erated by the propeller 7 and the side skegs 18 are lo- rear skegs improves. cated as far aft as possible. The side skegs 18 extend [0007] In accordance with an embodiment, the ship is downwards at least to under the largest depth of the hull according to claim 7. In this way, the rear skegs have a 8 and in the shown embodiment they extend as deep as minimal flow resistance. 55 the propulsion and steering units 6. The distance be- [0008] In accordance with an embodiment, the ship is tween the side skegs 18 is considerable so that during according to claim 8. In this way, the stabilizing effect of sailing of the tug 1 there is a stable flow of water between the rear skegs increases during straight course sailing the side skegs 18. In the shown embodiment, the side 2 3 EP 2 371 701 A1 4 skegs 18 are positioned at approximately 0,25 times the 4. Ship in accordance with claim 1, 2 or 3 wherein each width of the vessel from the centre line of the tug 1; the of the rear skegs (18) extends in a propulsion jet of distance between the side skegs 18 is at least a propeller one of the propulsion and steering units (6) when the diameter. horizontal rotation-axis (5) of the propeller and steer- [0015] The side skegs 18 have a profiled shape with 5 ing unit is directed rearward and parallel to the hull’s a rounded front and ending with a minimal thickness. longitudinal axis. Such a profile ensures a flow that makes an inflow angle with the longitudinal centreline of the side skeg 18 gen- 5. Ship in accordance with claim 1, 2, 3 or 4 erates a lift force. A suitable profile for the described em- wherein the rear skegs (18) have a height extending bodiment is a NACA 0018 profile, which makes an inflow 10 the depth of the hull (8). angle of approximately 14° possible without loss of lift force. A similar profile with an increased thickness would 6.