FIELD OF INVENTION
The present invention relates to design modifications & its successful implementation in Landing Craft Utility (LCU MKIV) Vessel. These innovations relate to mitigation of severe aeration by an Inverted Spray Rail configured for obstructing bubbles from flowing down the hull by diverting the same towards the sides of the vessel thereby achieving flawless Echo Sounder Performance. It also relates to improvisation of astern motion by introducing a unique Forward Skeg enabling unhindered beaching operation.
BACKGROUND ART
Echo Sounder Non Performance: After first Sea Trial of the vessel it emerged that the problem is more severe for LCU MK IV. After certain speed all the Echo Sounders stopped functioning due to presence of two phase flow below echo sounders.
Functioning of Echo Sounder is a prerequisite for sailing and its non-performance due to Aeration is a severe problem for ships. Further, lack of worldwide technical literatures on the subject matter had made the mitigation task more challenging.
Directional stability: For facilitating beaching operations, the vessel is designed with rake in keel of 1 in 60, though this is also a concern for such vessels as it entails issues pertaining to directional stability; especially in astern motion. This was also observed during first sea sortie wherein the vessel had issues pertaining to directional instability in astern motion.

OBJECT OF INVENTION
The principle object of the present invention is to provide improved echo sounder performance. The invention adopts mitigation strategy to completely divert the substantial two phase flow going underneath the hull for successful operation of Echo Sounder.
Another object of the present invention is to provide improved directional stability in Astern. The theoretical analysis of the problem demanded a requirement of increasing longitudinal sectional area in the forward of the vessel to improve the directional stability of the vessel during astern motion/unbeaching operation.
Hence, strategies were envisaged to design, develop, test and successfully implement the profound solutions to mitigate the issues.
SUMMARY OF INVENTION
The present invention relates to design and implementation of an Inverted Spray Rail & Forward Skeg configured for successfully obstruction of the bubbles from flowing down the hull by diverting the same towards the sides of the vessel thereby achieving flawless Echo Sounder Performance and improve astern motion.
An inverted spray rail enables a vessel to successfully obstruct the bubbles from flowing down the hull by diverting the same towards the sides of the vessel thereby achieving flawless Echo Sounder Performance. Introduction of forward inverted spray rail was beneficial especially for these vessels (like LCUs) wherein primary features such as operating

at low draft, forward Bow ramp & rake of keel were mandated for Vehicular Movement & Beaching requirement and fitment of any conventional items underneath the hull like Gondola or Blister for successful functioning of Echo Sounders could be major limiting factor for beaching operations for any Landing Crafts.
In another exemplary embodiment, there is nose shape skeg provided in the forward portion of the vessel. The said nose shape forward skeg is configured for improving directional Stability during Astern Manoeuvring during un-beaching operation by increasing longitudinal sectional area in the forward of the vessel to maintain a straight line course while astern movement.
In another exemplary embodiment there is provision for fitment of Echo Sounder just beneath the Skeg where aeration effect is minimal as verified during CFD analysis & actual sea trials.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 illustrates flow vector of water particle in accordance with the present invention;
Fig.2 illustrates water to air mixture in accordance with the present invention;
Fig.3 illustrates the model test in accordance with the present invention;
Fig.4 illustrates the relocation of Echo Sounder position based on Model Test and CFD Analysis in accordance with the present invention;

Figs.5 & 6 Illustrates the manoeuvring test at NSTL (DRDO), Vizag with various Forward Skeg configuration to ascertain Directional Stability during Astern Motion in accordance with the present invention;
Fig.7 illustrates the forward skeg and Inverted Spray Rail fitted On-board in accordance with the present invention.
DETAILED DESCRIPTION
The Landing Craft Utility (LCU MK IV) Vessel for Indian Navy, is the World's largest operational vessel with highest speed of 15 knots. The Preliminary Staff Requirements of the vessel demanded a hull with rake of keel with flat bottom and a forward bow ramp. Requirement of beaching on shore demands a rake of keel. These requirements are contrary to some other requirements which are necessary considering the operational requirements of the vessel that includes High-speed, Directional Stability and operability of Echo Sounder at all speeds.
INVERTED SPRAY RAIL
The applicants herein innovatively designed and implemented Inverted Spray Rails for successful obstruction of the bubbles from flowing down the hull by diverting the same towards the sides of the vessel thereby achieving flawless Echo Sounder Performance. The configuration of the inverted spray rails may consist of multiple inverted spray rails depending on various aspects, viz, speed, bow shape, etc of the vessel.

Introduction of forward inverted spray rail was beneficial especially for these vessels (like LCUs) wherein primary features such as operating at low draft, forward Bow ramp & rake of keel were mandated for Vehicular Movement & Beaching requirement and fitment of any conventional items underneath the hull like Gondola or Blister for successful functioning of Echo Sounders could be major limiting factor for beaching operations for any Landing Crafts.
NOSE SHAPED FORWARD SKEG
Flat Bottom Ships like Tankers, LSTs and LCUs are prone to directional instability especially during astern manoeuvring. Vessels like LCUs which engages on its own power for combat unbeaching operations and the fitment of innovatively designed nose shaped forward skeg has provided following benefits without affecting beaching requirements (In non-combat operation, the vessel use Stern Anchor with Aft GP Winch for pulling the vessel out of beach during astern):
(i) Improvement in directional Stability in astern manoeuvring during unbeaching Operation by increasing longitudinal sectional area in the forward of the vessel to maintain a straight line course during astern motion.
(ii) Provision for fitment of Echo Sounder in the forward skeg where aeration effect was minimal as verified during CFD analysis.
The de novo design of inverted spray rails have the capability to obstruct the bubbles from flowing down the hull by diverting the same towards the sides of the vessel thereby

achieving flawless Echo Sounder Performance. The innovative Nose Shaped Skeg at forward region has aided improvement in directional Stability in Astern Manoeuvring during unbeaching Operation of the vessel LCU MK IV.
The in-house design expertise formed the basis of success of the invention. All the analysis and study involved in the project for validating these innovations were either carried out in-house or using the model testing & CFD analysis facilities present in India, which has led to saving of foreign exchange.
IMPROVEMENT OF ECHO SOUNDER PERFORMANCE
CFD analysis had been carried out to understand the air bubble flow pattern, Fig. 1 illustrates the flow vectors of water particles and Fig.2 illustrates the ratio of water to air mixture. The numerical results were verified with physical model testing using a scaled down model of the ship hull at IIT Kharagpur (Fig. 3). Based on the analysis carried out, location and sizing of Inverted Spray rails were finalised and accordingly echo sounders were relocated from previous position to new location, i.e., one echo sounder in forward skeg and another beside the forward skeg (Fig. 4). Sizing and internal angle of the spray rail was finalized based on experimental study done at IIT Kharagpur using model tests. Operability of echo sounders has been demonstrated during sea trials to the customer and Class.
IMPROVEMENT IN DIRECTIONAL STABILITY
Flat Bottom Ships like Tankers and LCUs are prone to directional instability

especially during astern manoeuvring. Theoretical analysis of the problem demanded a requirement of increasing longitudinal sectional area in the forward of the vessel to maintain a straight line course during astern. Skeg was introduced in forward section of hull. Extreme care has been taken while designing Skeg arrangement w.r.t. location and sizing considering beaching requirement of the vessel even considering a steep beach gradient of 1:20. Various combinations of forward Skeg size were model tested to get the optimal result. However, the final design of forward skeg and inverted spray rail (P&S) considered for fitment are illustrated in Fig.7 After the changes undertaken, the vessel has been able to achieve the required directional stability during aft movement and the same has been demonstrated to the customer and Class during Sea trial. The manoeuvring test at NSTL (DRDO), Vizag with various Fwd Skeg configurations to ascertain Directional Stability during Astern Motion is illustrated in Figs.5 & 6.
INDUSTRIAL APPLICATION
The combination of Inverted Spray Rails and Nose shaped Skeg at Bow region could be effectively used for flat bottom vessels like LCUs which have aided
a. Operations in restricted drafts.
b. Beaching/Unbeaching requirement.
c. In mitigation of aeration which is prominent due to presence of two phase flow
under the hull.

d. In functioning of echo sounders without fitment of any conventional append
ages like Gondola or Blister which would have required to overcome aeration
problems otherwise.
e. In improvising directional stability during astern Manoeuvring.
Although the foregoing description of the present invention has been shown and described with reference to particular embodiments and applications thereof, it has been presented for purposes of illustration by way of examples and description and is not intended to be exhaustive or to limit the invention to the particular embodiments and applications disclosed. The particular embodiments and applications were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such changes, modifications, variations, and alterations should therefore be seen as being within the scope of the present invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

We claim:
1. A Landing Craft Utility Vessel with flat bottom comprising of:
an Inverted Spray Rail (P&S) fitted at the forward of the said vessel configured for obstruction of the bubbles from flowing down the hull by diverting the same towards the sides of the vessel;
a nose shaped forward skeg configured for providing directional stability during astern maneuvering.
2. The Landing Craft Utility Vessel as claimed in Claim 1, wherein a plurality of said Inverted Spray Rails are fitted at the forward of the said vessel.
3. The Landing Craft Utility Vessel as claimed in Claim 1, wherein the said inverted spray rail completely diverts the substantial two phase flow going underneath the hull for successful operation of Echo Sounder.
4. The Landing Craft Utility Vessel as claimed in Claim 1, wherein the said nose shaped forward skeg is made at the forward section of hull aiding improvement in directional stability in astern maneuvering during un-beaching operation of the vessel.
5. The Landing Craft Utility Vessel as claimed in Claim 1, wherein the forward skeg arrangement is configured to beach the vessel on shore with a steeper gradient up to 1:20.

6. The Landing Craft Utility Vessel as claimed in Claim 1, wherein fitment of echo sounders is made in forward skeg and/or beside the forward skeg enabling operation of forward echo sounders due to absence of aeration in that region.
Dated this 18th day of January, 2019.