Operational Safety And Towing Of Damaged Vessels In Naval Architecture

Introduction to Operational Safety in Naval Architecture

Operational safety remains the most serious concern in naval architecture. When a vessel is damaged, it is very hard to know the vessel’s stability because the motion of damaged vessel is exceedingly coupled with the flooding water behavior. Its motion is affected by the flooding water, and ironically, the flooding water motion is influenced by the motion of the ship. Among many to achieve quality operational safety standards such factors as hull stability and safety requirements are to be put into consideration (Sikora, 2005).

To protect the steel monohull survey vessel of 20.5m LOA from further damage that may be caused by the leaking seawater through the hole in the vessel which is In the way of a freshwater tank, as the surveyor in charge, I must ensure that the vessel is tow voyaged across the open sea to a place of repair and be repaired. This must be done with strict adherence to the requirements of the Flag State Administration which states that temporary repairs must be performed in the first instance, or the vessel to be towed unmanned.

The process involves offering requisite advice on the necessary repairs as well as supervision on behalf of the client. In addition, it encompasses advice on matters to do with stability and the survivability of the towed and towing vessel, installation of a new deck crane on the port side of the small craft at the midsection, preparation procedure for the towing survey of the small craft and another survey at the location of repair, and to weigh how the emergency salvage capacity will influence the level of risk involved. This activity will involve safe emergency towage capacity and the ability to respond to the recovery of the damaged vessel (Ritter, 2012).

Normally, a floating object possesses some degree of stability and buoyancy. These two parameters are exceedingly important considerations with respect to the safety of any water vessel. The aforementioned parameters are also important with respect to limitations of operation of this damaged vessel. Stability and buoyancy are the factors that enable a ship to stay afloat on water by applying the Archimedes principle. If this damaged vessel is towed in a damaged condition, water flooding will occur in the deck causing a phenomenon known as a surface effect which will create a deleterious effect on the stability of the vessel and eventually cause the vessel to capsize easily. As the professional hired it is within my jurisdiction to ensure that the ship is not damaged further and it reaches its place of repair within the stipulated time and a proper repair is done.

Survivability refers to the ability of the vessel to remain afloat, and in stable state as thinkable when a state of flooding erupts. The survivability of the craft will depend on a number of such factors as the mass of water in the structure of the ship hull, the water location in the structure of the ship hull and the water effect known as the free surface effect (Cerup, 2009).

Means of survivability

• The overall orientation of the small craft will be critical to influencing its capability to thwart water ingress and, to avert water flow through the structure should a floating situation occur.
• Reduce the ability and possibility of flooding by having a sound understanding of the abilities of the vessel, maximum weather conditions and the area of operation which is the 160 nautical miles open sea. The design of the vessel should let water to freely flow off the main deck back to the sea via the freeing ports.
• By making the most of the down flooding angle of the vessel, survivability of the vessel can be increased.
• Bilge pumps aid to reduce the volume of water. This will assist in maintaining stability and survivability for the longest possible period of time prior to the loss of the vessel just in case.
• Watertight bulkheads are significant to the vessel’s survivability since a vessel that is not fixed with any waterproof bulkhead will flood (Andrews, 2008).

Stability.

Stability, on the other hand, refers to the ability of the vessel to endure loading and return to upright position. In a damaged state, the residual stability must be in a way that:

• Equilibrium angle doesn’t surpass 7 degrees from the vertical position.
• The consequential righting lever curve possesses a range to the depression flooding angle of 15 degrees past the equilibrium angle.
• Full righting lever in this range is more than 100mm.
• Area covered by the stability curve is not below 0.015-meter radians.
• The destruction and flooding should not make the vessel to float at a watermark of below 75mm to the weather deck at whichever point (Chose, 2006).

Towing a Damaged Vessel for Repair

The research involving towing of a damaged vessel in various conditions of damage, especially like in our case, contact destruction at the waterline in the region of the starboard forward hull show that this operation may be very difficult and the forces necessary to tow such a vessel might in certain circumstances be exceedingly huge. This needs the employment of powerful tugs having a huge bollard pull. Usually, there will be also difficulties with bringing heavy towing hawser onboard of the damaged vessel (Sieleski, 2012).

In order to avoid further damage to the vessel, disastrous pollution of the sea, and preventing further entry of seawater into the freshwater path, the floodable area of the vessel must be reduced and this is done by fitting transverse watertight bulkheads throughout the structure. This is done to increase its survivability but care must be taken when considering the use of longitudinal watertight bulkheads. The floodable area is reduced and the effects of water weight as well as the free surface effect. In addition, watertight bulkheads also reduce the capacity required by the bilge pumps or emergency bilge suctions (Lang, 2006).

To ensure that the towed and the towing vessels are qualified for a towed voyage, certain parameters for towed and the towing vessels must be covered. For the towing vessel, such factors as tug type, bollard pull, pivot point, length of towing line, and tug stability which is established by the heeling moment arising during towing and the applied safety margin amongst others must be taken care of as per the regulations of the Flag State Administration. It is important to be aware of the rules vital for the inspection and testing of the towing equipment and gear. By putting all these parameters together, the authorities will do nothing but to certify the towing process (Deakio, 2005).

During the final repair, it is crucial to know the original damages before tow voyage and the final damage at the end of the voyage. This would help to define the types and extent of damage on the vessel. Firstly, drain all the water that might have gained entry into the vessel through the overboard by means of a bilge pump. This is followed by examining the extent of damage to the hole. Examining the extent of damage is equally important since it will help do determine the type of damage, the tools required for the repair and the type of workmanship needed, without forgetting the size of the workmanship.

Survivability and Stability Considerations

Since the vessel is made of steel, it’s advisable to use the techniques of steelwork such as welding to seal the hole. Therefore, a metal worker with vast experience in ship welding will be hired to do the job. Care needs to be taken during the process so that no further damage is caused to the craft. For the damaged fresh waterway, replace the damaged part with a new one. Ensure that the new freshwater way is perfectly fitted and no water is leaking. This is essential because the freshwater should not come into contact with the sea water once the boat has been repaired. Then drain all the water in the tank, clean the tank with fresh water then refill with a clean one (Daidola, 2007).

Regardless of the role and type of deck machinery fitted to any vessel, there is a common concern which is the means and condition of attachment to the vessels structure. Therefore, with regards to this damaged vessel, during the survey of the deck crane as the surveyor, I am mindful that the foundations of the machinery will exist largely below decks and requires to be visited via entries to void spaces, ballast tanks or similar confined spaces (Trincas, 2010).

Preparation for the survey entails that all the necessary resources are assembled. These include all the equipment for tests and repair and human resource to aid in the work involved. For the towing process, a tugboat is to be availed and any tug type in good condition can do the job. Proper preparation for the survey is critical to this exercise. Therefore it is important to maintain quality operation at each stage involved.

In each stage of my involvement in this job, as a professional duty, it’s my responsibility to certify that my client is contented with my commitment by showing sincere commitment and due diligence to the operation. Furthermore, as a professional responsibility, I would let my client be close in this task as this would help me to get such genuine data about this vessel as the number of times the vessel has been involved in a similar incident, and much more information about the same (Gore, 2007).

Unlike the cases of undamaged stability, the valuation of the stability of a broken vessel is a very complex physical occurrence. Hence it’s extensively recognized that computational fluid dynamics (CFD) method is among the best practicable methods. With an aim of progressing enhanced approaches of CFD for the valuation of broken stability, thus it’s important to execute properly made test model as well as constructing a CFD validation record. In this case, free roll-decay tests on still seawater with both undamaged and damaged vessels are executed and six-degree-of-freedom (6DOF) motion responses of an intact ship in steady waves are measured. The impacts of the flooding water on the roll decay motion of the craft are examined through a free roll decay test. The record that offers 6DOF motion responses of the complete vessel in the model tests in steady waves is time-honored (Frangol, 2011).

Fitting Transverse Watertight Bulkheads to Reduce Floodable Area

Additionally, two measurement systems are used: flooding water behavior measurement and ship motion measurement systems. Primarily, the motion responses were measured with a grouping of the accelerometers and an inertial measurement unit (IMU). For the roll motion measurement in the free roll-decay test the IMU was used. The accelerometers were used to acquire (6DOF) motion responses from the tests outcomes in steady waves. Seven accelerometers with one situated at the center of gravity, two at the bow, two at the stern, one at the port, and one starboard of the model. From the accelerations read on the instrument, the (6DOF) motion results were achieved using strap down method. Moreover, five wave probes were used to measure flooding water height (Qi, 2004).

To respond to a curious person who wants to know about the operations to be undertaken, cost of the operation, as well as the factors that led to the damage of the ship, the initial step is to ensure having a professional plan and structure on how to go about the issue in a rather effective way without being flippant. Considerately, dismissing the person would be the best option, but in a rather polite and/or humorous manner, owing to the fact that time is of the essence and any distraction would cost the operation time (Kaharal, 2005).

Conclusion

With respect to this exercise, the main objective is to transfer the damaged monohull survey vessel to a place of repair that was across the 160 nautical miles open sea and subsequently do the repair. This became a success as the small craft was towed to its destination and the operation was carried out in strict adherence to the Flag State Administration regulations which requires that provisional repairs are performed in the first case or the ship be towed unmanned. In this activity, a series of tests were performed to build a dependable record for the damaged vessel’s stability and survivability. Measured time pasts of vessel’s motion and flooding behavior were systematized as a database for computational fluid dynamics validation (Brizola, 2003).

A test known as free roll decay was done in the broken monohull vessel to investigate the interaction between the vessel’s roll motion and the flooding water. The damping coefficient of the vessel became big since it was broken. The amplitude of roll motion reduced more swiftly since the flooding water would act like an anti-rolling tank. In order to avoid further damage to the vessel, disastrous pollution of the sea, and preventing further entry of seawater into the freshwater path, the floodable area of the vessel must be reduced and this is done by fitting transverse watertight bulkheads throughout the structure. This is done to increase its survivability but care must be taken when considering the use of longitudinal watertight bulkheads.  In addition, watertight bulkheads also reduce the capacity required by the bilge pumps or an emergency bilge suction (Utama, 2010).

References

Andrews, D.J. and Zhang, J.W., 2008. Trimaran Ships the Configuration for the Frigate of the Future. Naval engineers journal, 107(3), pp.77-94.

Brizzolara, S., Capasso, M., Ferrando, M., Podenzana-Bonvino, C., Cardo, A. and Francescutto, A., 2003. Trimaran hull design for fast ferry applications. In Proceedings of the International Conference on Ship and shipping research, NAV (pp. 10-1).

Cerup-Simonsen, B., Törnqvist, R. and Lützen, M., 2009. A simplified grounding damage prediction method and its application in modern damage stability requirements. Marine Structures, 22(1), pp.62-83.

Daidola, J.C., Graham, D.A. and Chandrash, L., 2007, January. A simulation program for vessel’s maneuvering at slow speeds. In Ship Technology and Research Symposium (STAR), 11th.

Deakin, B., 2005. An Experimental Evaluation of the Stability Criteria of the HSC Code. In International Conference on Fast Sea Transportation, FAST.

Deakin, B., 2010. Collating evidence for a universal method of stability assessment or guidance. Trans RINA, 152.

Frangopol, D.M., Bocchini, P., Decò, A., Kim, S., Kwon, K., Okasha, N.M., Saydam, D. and Salvino, L.W., 2011, September. Life-cycle ship reliability assessment, damage detection, and optimization. In Proceedings of the 11th International Conference on Fast Sea Transportation-FAST 2011 (pp. 26-29).

Ghose, D.J., Nappi, N.S., and Wiernicki, C.J., 2006. Residual Strength of Damaged Marine Structures (No. SR-1341). DESIGNERS AND PLANNERS INC ARLINGTON VA.

Gore, J.L., 2009. SWATH ships. Naval engineers journal, 97(2), pp.83-112.

Kaharl, V., 2005. SWATH: Calm seas for oceanography. Eos, Transactions American Geophysical Union, 66(36), pp.626-627.

Lang, T.G., Bishop, C.B. and Sturgeon, W.J., 2006, October. SWATH ship designs for oceanographic research. In OCEANS’88. A Partnership of Marine Interests. Proceedings (pp. 1163-1168). IEEE.

Qi, E.R. and Cui, W.C., 2001. A state-of-the-art review on ship collision and grounding. Journal of Ship Mechanics, 5(4), pp.67-80.

Ritter, F.A.B.I.A.N., 2012. Collisions of sailing vessels with cetaceans worldwide: First insights into a seemingly growing problem. Journal of Cetacean Research and Management, 12(1), pp.119-127.

Sielski, R.A., 2012. Ship structural health monitoring research at the Office of Naval Research. JOM, 64(7), pp.823-827.

Sikora, J.P., 2005. A method for estimating lifetime loads and fatigue lives for swath and conventional monohull ships. Naval Engineers Journal, 95(3), pp.63-85.

Trincas, G., Zanic, V. and Grubisic, I., 2010. COMPREHENSIVE CONCEPT DESIGN OF FAST TO-RO SHIPS BY MULTI-ATTRIBUTE DECISION-MAKING.

Utama, I.K.A.P., Santosa, P.I., Chao, R.M. and Nasiruddin, A., 2013. New concept of solar-powered catamaran fishing vessel. In Proceeding of the 7th International Conference on Asian and Pacific Coasts (pp. 903-909).