Ships – Steering mechanism – Fluid pressure
Patent
1998-09-08
2000-06-27
Swinehart, Ed
Ships
Steering mechanism
Fluid pressure
114246, 440 67, B63H 2546
Patent
active
060793465
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a tugboat having azimuthal propelling units.
Within the framework of the present invention, by the expression "azimuthal propelling unit" is meant a propelling unit whose propelling direction in horizontal direction can be varied through 360.degree.. Such azimuthal propelling units are already known per se, for instance in the form of a nozzle having a screw arranged therein.
Specific requirements are imposed on a tugboat with regard to thrust and maneuverability. For instance, it is desired that a tugboat cannot only produce hauling power in forward direction, but also in rearward direction, and even in lateral direction, although the hauling power producible in lateral direction will be less than the hauling power producible in longitudinal direction.
For instance from the article "Schottel tugs" in Small Ships, Vol.99, No.1204, December 1976, page 95, it is already known to fit a tugboat with azimuthal propelling units because of the maneuverability provided thereby. Such tugboats, also known by the name of "tractor tug", have two azimuthal propelling units which are juxtaposed in transverse direction and, viewed in the longitudinal direction of the tugboat, in a central position. However, some drawbacks are attached to this. For instance, it is not properly possible to continue using the tugboat if one of the propelling units has been damaged.
Generally, the object of the invention is to provide a tugboat which, in respect of the above-mentioned aspects, performs better than the tugs known thus far.
In particular, the object of the invention is to provide a tugboat which is less susceptible to damage, or at least has still good utility in the event of failure of one of the propelling units. A further object of the invention is to provide a tugboat which can travel economically, in particular by utilizing not all propelling units present.
A further object of the invention is to provide a tugboat which can produce more power than the "tractor" tugs known thus far, without the draft being increased. In known "tractor" tugs, an increase of the power producible can be realized by using two stronger propelling units, but a consequence thereof is that the dimensions of the propelling units are increased as well, which has an adverse effect on the draft of the ship.
Another problem concerns the fire extinguishing installations on board a tugboat, intended for extinguishing a fire on shore or on board other ships. In order to meet specific requirements (Fifi 1), a tugboat has two fire extinguishing pumps, driven by the propelling engines. During the use of the fire extinguishing pumps, those engines run at full power. Consequently, without countermeasures, the propelling units would produce thrust at full power, which is of course undesired. On the other hand, in conventional tugs, it is not possible to switch off the propelling units completely by uncoupling them from the associated engines, because the propelling units have to produce a counterforce to the force exterted on the boat by the fire extinguishing water, to enable the boat to be kept in position and/or displaced in a desired direction. The desired power of each propelling unit should be steplessly settable over a wide range, with the associated engine in each case running at full power, for which purpose a slip coupling should be included between each propelling unit and the associated engine. On account of the above-mentioned power requirements, such couplings are fairly expensive.
A further object of the present invention is to alleviate this problem as well.
In order to realize the above objectives, a tugboat according to the present invention has three azimuthal propelling units whose centers, viewed from the top, lie on the angular points of an isosceles triangle.
Thus, it is possible to produce a greater thrust which is distributed over the tugboat in a better manner. In comparison with known "tractor" tugs, that greater thrust can be realized through the use of smaller propelling units, as a result of which the tugbo
REFERENCES:
patent: 3176645 (1965-04-01), Shatto, Jr.
patent: 3548775 (1970-12-01), Hammond
patent: 4175511 (1979-11-01), Krautkremer
Sar Holding N.V.
Swinehart Ed
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