BACKGROUND OF THE INVENTION
Field of Invention
Description of Prior Art
This invention relates to a marine vessel, and more particularly, to a landing craft that
uses fixed and retractable azimuthing drives in combination with an improved bow shape to
obtain both excellent seakeeping and beaching abilities.
Throughout the history of modem military operations, there has been a requirement to
transfer men and'materials from ships to a beachhead. Without docking facilities, such transfers
are difficult to accomplish. In the twentieth century, particularly during the Second World War,
specialized landing craft were developed to facilitate such transfers. Unfortunately, such craft
were limited to transporting a relatively small group of men, one or two vehicles, or an
inadequate amount of cargo, due to their limited size and cargo weight capacity. Larger marine
vessels were limited for such operations due to their inability to effectively and safely "beach"
themselves to unload cargo and then return to normal seakeeping operations.
Some of the aforementioned problems where addressed with the development of socalled
"roll-on, roll-off" vessels. Used in both military and commercial applications, vehicles
and other cargo are loaded onto a marine vessel, typically by way of a ramp on the bow or stern
of the ship. The vehicles or cargo are then unload by way of the same ramp used for loading.
An obvious disadvantage of using one ramp is that vehicles must be "rolled-on" in reverse, such
that they can be driven off the vessel in a forward orientation so that they can be immediately
When loading/unloading ramps are provided at both the bow and the stern of the ship,
such vessel still suffer from several disadvantages, particularly if used during beaching
operations. In such prior art vessels, vehicle, cargo, etc. were loaded at the stern of the ship.
Beaching operations were conducted with the bow portion of the ship being beached, and the
materials offloaded by a ramp or similar means at the bow. However, the use of ramps and other
offloading systems located on the ship's bow affected the seakeeping ability of the ship as design
compromises must be made to the hull design which affect the ability to sail through the water
and break waves. Furthermore, due to the compromised designs of such hulls, the bow ramps
would suffer damage from the force of wave impacts, beaching and general sailing operations.
Prior art landing craft are also destabilized by the surf slamming into the flat stern of the
ship when beached. When extricating from beach, such craft must operate in reverse―i.e., they
drive stern first into the surf, operating its propellers or other propulsion system in reverse.
Operation of the propulsion system in this manner is inefficient and taxing on the mechanical
systems. Once clear of the shallow draft of the beach area, such ships must perform a broad turn
to point the bow of the ship forward, towards the sea, for normal seakeeping operations. This is
difficult in rough surf and can result in loss of vessels during combat operations.
It is conventionally known in the art that steerable or azimuthing drives may be used to
orient marine vessels in different directions. U.S. Patent No. 5,522,335 to Veronesi et al.
describes a combined azimuthing and tunnel auxiliary thruster which can be retracted inside of a
boat hull if hazards are present, the contents of which are hereby incorporated by reference.
However, there is no discussion in Veronesi et al. of utilizing the disclosed thrusters in
combination with a vessel configuration which is appropriate for both seagoing and beaching
U.S. Patent No. 5,660,131 to Gulling, et al. describes an icebreaking attachment for use
with a parent vessel. This attachment, when connected to the parent vessel, provides an ice knife
at the bow for increased icebreaking ability and protection. The icebreaking attachment also
provides fully rotatable z-axis drives to steer the parent vessel, or the icebreaking attachment
alone when detached, during icebreaking operations. While incorporating conventionally known
z-axis drives to increase maneuverability, the disclosure of Gulling, et al. does not contribute to
the problems associated with prior art landing craft.
Another representative example of a marine vessel utilizing steerable drives is U.S.
Patent No. 5,966,520 to Arpiainen, et al. which discusses an icebreaking method and icebreaker.
The icebreaker of Arpiainen, et al. uses a relatively narrow hull and first and second propulsion
mechanisms to propel the icebreaker through an ice field in a direction at a substantial angle to
the keel line of the ship to open a wide opening in the ice. Again, while the use of steerable
drives is discussed, the apparatus and method of Arpiainen does not disclose how such drives, or
the hull configuration of the ship, can be used to accomplish beaching operations while
maintaining good seakeeping abilities.
It is therefore an object of the present invention to provide a marine vessel that is capable
of engaging in beaching operations and maintain good seakeeping abilities while doing so and
when traveling in open water.
It is a further object of the present invention to provide a marine vessel that is capable of
moving in multiple directions including traveling bow forward as well as stern forward.
It is yet another object of the present invention to provide a marine vessel which cargo
can be loaded and unloaded quickly and easily.
SUMMARY OF INVENTION
An additional object of the present invention is to provide an agile craft capable of
turning in a short radius and handling well in surf and landing operations.
The marine vessel described herein has the ability to travel in multiple directions,
particularly stern forward, during landing operations on a beach or other unimproved water/land
interface. The high maneuverability of the disclosed marine vessel is accomplished through the
use of conventional steerable or azimuthing drives mounted below the waterline on the bow and
stern portions of the craft.
Unlike prior landing craft, which beach bow first, the ship disclosed herein uses the
combination of fixed and retractable azimuthing drives to beach the vessel stern first. The stem
azimuthing drives are adapted to retract into the hull of the ship such that they are not damaged
by the shallow waters in the beaching area.
The first advantage of this system is it allows a "drive-through" cargo deck. Vehicles,
such as tanks, trucks, and humvees, are driven into the cargo area at a loading depot from the
bow. The front of the vehicles will then face towards the stern of ship. Once the ship is beached
at the designated landing zone, the vehicles can drive off the ship, right onto the beach in a
forward gear. By unloading vehicles and other cargo astern of the vessel, the bow of the ship can
be designed for excellent seakeeping and wave breaking ability since it is not used for beaching.
This feature is also effective for getting on and off the beach since the effects of high surf near
the beach are minimized because the efficient, wave breaking bow of the vessel is pointed
towards the surf. This eliminates the problem with past landing craft and logistic support
vehicles that have had problems getting on and off the beach due to the flat stern slamming into
the surf or being pushed by the surf while beaching.
BRIEF DESCRIPTION OF THE DRAWINGS
The azimuthing drive propulsion system adds two advantages over traditional drive
systems. First, the bow azimuthing drives provide the capability of full bollard thrust in both
directions and are therefore extremely effective for powering off a beach. Second, with at least
three drives operating (bow and stern), the vessel has full dynamic position capability while at
Specific embodiments of the invention have been chosen for purposes of illustration and
description, and are shown in the accompanying drawing, forming a part of the specification
- FIG. 1 shows a side view of a symmetric vessel according to the invention
- FIG. 2 shows a front, or bow, profile view of a vessel according to the invention.
- FIG. 3 shows a rear, or stern, profile view of a vessel according to the invention.
- FIG. 4 shows a cut-away view of the stern end of the vessel according to the invention
illustrating the stern azimuthing thrusters in operational and retracted positions.
- FIG. 5 shows a perspective view of the bottom of the vessel according to the invention.
- FIGS. 6A-B show top cut-away views of an alternative embodiment of the vessel according to
the invention containing clamshell doors on bow of the vessel.
- FIGS. 7A-C show the beaching procedure of the vessel according to the invention.
- FIGS. 7D-E show extracting the vessel according to the invention from a beach.
- FIG. 8 illustrates a panoramic view of beaching operations utilizing the vessel according to the
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to Fig. 1, vessel 10 generally contains a boat hull 30 having a bow portion 12, a
stern portion 14 and a keel 26. Located at the bow 12 is a bow ramp 16. The bow ramp 16 is
generally used to load vehicles or other cargo onto the vessel 10. Located at the stern 14 is a
stern ramp 18 that is generally used to offload vehicles or other cargo, particularly during
beaching operations. Below the waterline of the vessel 10 are two sets of azimuthing or
steerable thruster drives 20 and 22. At least one drive 20 is located on the bow portion 12 or the
vessel. Similarly, at least one drive 22 is located on the stern portion 14 of the vessel. In the
preferred embodiment of the invention, vessel 10 contains two bow thrusters 20 and two stern
thrusters 22. However, as shown in FIGS. 2 and 3, one stern thruster 22 may be used in
combination with two bow thrusters 20.
Referring to FIGS. 1 and 2, the bow portion 12 of the vessel 10 incorporates, to the extent
possible, characteristics of a well designed sea-going vessel. The bow portion shape is ship-like
(i.e., not flattened to accommodate a beaching ramp), having a deep forefoot and fine "V"
sections on the port and starboard sides of the bow.. The bow end 12 is also fitted with a bulb 24
to reduce calm water resistance. The bow ramp 16 and deck 28 are r above the waterline unlike
prior art landing craft. This allows an improved ship-like shape of the bow and serves to
prevent damage to the bow ramp 16 during seakeeping operations. As a result of this design, the
bow portion 12 is optimized for a high-sea-state environments resulting in improved
controllability and performance of the vessel 10. Further, when extracting the ship from a beach,
the bow portion 12 is facing seaward to reduce wave impacts and the vessel 10 does not have to
be turned around to return to sea.
Referring to FIGS 1 and 3, the stern portion 14 of the vessel 10 incorporates features that
are designed to enhance the movement of vehicles and other cargo onto a beach. The deck 28 is
close to the waterline, which serves to reduce ramp 18 length and break angle, or the angle
between the deck and the beach. As is shown in FIGS. 1 and 3 the stern portion bottom shape
is flat and broad, improving the stability of the vessel 10 when beached.
In the preferred embodiment of the invention, the azimuthing drives 20 and 22 are
powered by DC electric motors 30, as shown in FIG. 4 The azimuthing drives are
conventionally known in the art and may be obtained from several producers such as Rolls-Royce
(United Kingdom) and John Crane-Lips (United Kingdom). The stem end thrusters 22
can be retracted into the vessel hull 30 such that they are above the keel 26. This operation is
shown in shadow in FIG. 4. Any typical means for retracting the stern thrusters 22 into the hull
30 may be used, such as hydraulic lifts or mechanical lifts. This allows efficient beaching
operations without damaging the stern thrusters 22 on the beach/sea floor. The stem thrusters
22 are also fitted with fixed pitched propellers, which are optimized for open water speeds. In
contrast, the bow end thrusters 20 are non-retractable. In the preferred embodiment, the bow
thrusters 20 are also fitted with fixed pitch propellers which are mounted in nozzles optimized
for maximum bollard (zero speed of advance) thrust. In open-sea or transit conditions, 60% of
the power is preferably directed to the stern end thrusters 22 while the other 40% of power is
directed to the bow thrusters 20. In the preferred embodiment of the invention, this is done
because the stern end thrusters 22 have a higher propulsive efficiency and the bow end thrusters
are limited in diameter and therefore would be prone to cavitation if more power was applied.
Because, by their very nature, azimuthing thrusters have complete rotation about a vertical axis,
the direction of the vessel is preferably changed by movement and/or different directional
alignment of the bow and stern thrusters. This configuration is shown in FIG. 5. which shows
the bow thrusters 20 and stern thrusters 22 at different angles. However, as is known in the art
the vessel may also be turned through the use of variable power to the thrusters when all are
facing the same direction, i.e., all are pointing to the stern of the ship.
In general, the waterline of the vessel is fairly fixed, particularly during open sea
operations. The ship also has an operating draft, defined herein as the distance between the keel
26 and the sea floor. The operating draft generally varies, depending on the distance between the
sea floor and the top of the water. Quite obviously, when closer to the beach, the operating draft
is reduced. To further decrease or increase the operating draft during beaching operations, the
vessel of the instant invention contains an adjustable ballast and means to adjust such ballast. As
is know in the art, tanks or other storage areas are located throughout the ship, such that the
operating draft of the ship can be lowered or raised by adding or removing ballast, typically sea
water, from the ballast tanks. The adjustable ballast system assists extraction of the vessel from
the beach upon completion of unloading operations by allowing the stern portion 14 of the
vessel, and to lesser extent the bow 12, to float off of the beach.
In another embodiment of the invention, shown in FIGS.6A and 6B, the bow portion of
the ship 12 may be additionally fitted with clamshell doors 34 ahead of or proximal to the bow
ramp 16. Preferably, the clamshell doors 34 are split and open vertically, i.e., to the port and
starboard sides of the ship, as shown in FIG. 6A. FIG. 6B illustrates the clamshell doors 34 in
the closed position. When at sea, the vessel 10 will certainly experience repeated wave impacts
to the bow ramp 16 which will slow the vessel and may ultimately damage the bow ramp. The
addition of clamshell doors will protect the ramp and provide an even truer ship-shaped bow 12.
The operation of the previously disclosed structures in connection with beaching
operations is shown in FIGS. 7A-E and FIG. 8. In FIGS. 7A-E, the heavy arrow, in all cases,
points to the direction of the beach. Referring now to FIG. 7A, the vessel 10 is in open water
36 approaching the beach 38 (not shown) with the bow 12 pointed toward the beach. Bow
thrusters 20 and stern thrusters 22 are pointed toward the stem portion 14 of the vessel Once the
vessel reaches a predetermined distance from the beach, the thrusters 20 and 22 are turned, such
that the stern 14 is pointed toward the beach, as shown in FIG. 7B. The stern thruster 22 is
retracted into the hull 30 while the bow thruster 20 is pointed towards the bow 12 (i.e., the open
sea). The vessel 10 is shown beached in FIG. 7C. The stern 14 of the vessel is on the beach 38
while the bow is still floating in the water 36 with the bow thruster 20 inactive. The stern ramp
18 is lowered upon the beach 38 for cargo unloading. FIG. 8 illustrates a beached vessel 10 on
unloading tanks 40 upon the beach 38 by way of stern ramp. A second vessel 110 is shown in the
When the beaching operations are complete, the vessel 10 is extracted from the beach.
As shown in FIG. 7D, the stern ramp 18 is retracted and the bow thruster 20 is oriented toward
the beach. By removing ballast and operating the bow thruster 20, the ship is extracted from the
beach. Once the vessel is sufficiently clear of the beach, the stern thruster 22 deploys from the
hull 30, and in combination with the bow thruster 20 propels the vessel away from the beach and
toward open water.
In addition to the structures, sequences, and uses immediately described above, it will be
apparent to those skilled in the art that other modifications and variations can be made the
method of the instant invention without diverging from the scope, spirit, or teaching of the
invention. Therefore, it is the intention of the inventors that the description of instant invention
should be considered illustrative and the invention is to be limited only as specified in the claims
and equivalents thereto.