Conceptual design of a 20 TBP port tugboat for the " Bahía Málaga " ARC Naval Base

Resumen Diseño conceptual de una embarcación tipo remolcador de puerto de 20 TBP para la Base Naval ARC "Bahía Málaga" Date Received: November 18th 2018 Fecha de recepción: Noviembre 18 de 2018 Date Accepted: January 6th 2019 Fecha de aceptación: Enero 6 de 2019 Conceptual design of a 20 TBP port tugboat for the "Bahía Málaga" ARC Naval Base 1 Escuela Naval de Cadetes “Almirante Padilla”. Cartagena, Colombia. Email: orlando.royet@armada.mil.co 2 Escuela Naval de Cadetes “Almirante Padilla”. Cartagena, Colombia. Email: diego.orozco.ho@armada.mil.co DOI: https://doi.org/10.25043/19098642.178 Ship Science & Technology Vol. 12 n.° 24 (39-48) January 2019 Cartagena (Colombia) 40 This project seeks to carry out the conceptual design of a port towing unit to provide assistance to the sailing, mooring, and movement maneuvers of vessels in waters restricted by the channel. The main objective is to study the design of a bay tug with a capacity of 20TBP (Ton Bollard Pull), in order to acquire it for the Pacific Naval Base (BN2), considering that at the moment, the Pacific Naval Force does not have a tug type unit.

This project seeks to carry out the conceptual design of a port towing unit to provide assistance to the sailing, mooring, and movement maneuvers of vessels in waters restricted by the channel.The main objective is to study the design of a bay tug with a capacity of 20TBP (Ton Bollard Pull), in order to acquire it for the Pacific Naval Base (BN2), considering that at the moment, the Pacific Naval Force does not have a tug type unit.

General objective
Carry out the conceptual design of a tugboat with a capacity of 20TBP (Ton Bollard Pull) for the Bahía Málaga Naval Base, in order to assist the maneuvers of the surface units.

Specific objectives
1. Prepare the mission profile study, based on the requirements of the National Navy and define its main dimensions.2. Conduct research on port tugs with a 20 TBP capacity. 3. Design the shape lines as the basis for preliminary stability, maneuverability and intact stability calculations in order to determine the buoyancy of the tugboat.4. Estimate the ship's forward resistance and determine the power required in the propulsion system.
The work methodology will be through the use of the design spiral, which is cyclic and iterative, and seeks to establish and develop the concepts proposed in each phase of the project considering that these concepts have a direct relationship between them, therefore all considerations must be taken into account to define a concept, constantly reviewing the concepts in order to achieve a result that adapts to the characteristics experienced by the design spiral.Applying it in all the phases of the project, requires the development to be carried out point by point and relating to each one to reach its center or detailed design phase.
From the data, the tasks are developed sequentially and when the first round of the design spiral is completed, it can be said that the vessel has been defined at its preliminary design level.Every time the spiral goes through its completion of a new cycle, the corresponding task is deepened in its definition.
Within the design spiral (Fig. 1), the conceptual design of a 20TBP tug for the Malaga Bay Naval Base will be developed, comprising 8 booklets where each one will contribute to the final objective of delivering the "Ship Project" design listed in the following table : Its main function will be to tow and support the maneuvers of vessels that arrive, depart, change dock, transit through the channel, maneuvers restricted to vessels that require the assistance of the tugboat.This vessel has a bullard pull of 20 ton for a maximum operating capacity of 7500 tons deadweight.

Methodology
Mission profile In order to determine the main dimensions of the design, it was necessary to compile a database of existing vessels through diff erent means of information from which information was obtained from ten (10) vessels shown in the following data table: Th e defi nition of the ship shapes is of great importance in the design.From these shapes it the storage and handling needs of the cargo are verifi ed.Th e speed is also checked through diff erent procedures in the test channels or through the maxsurf software.
Th e shapes of the tug project are conditioned by the activity carried out by the vessel.Although it is qualifi ed as a cargo ship by the Classifi cation Society Guidelines, it is a ship that provides a service, so the cargo will not be decisive in the choice of its forms, but due to its design and function, the ship resistance must be reduced as much as possible.
According to the specifi cation, the project vessel is a conventional type tug that will perform assistance and support functions, which is decisive in the choice of design.Th ese processes are performed through computer simulation tools.One of the main advantages of using these tools is that it allows you to evaluate the possible modifi cations in the shapes at any time.

Shape lines
Th e Van Oortmerssen method was determined for this project, since it has much more correlation for this type of tugs, being an algorithm designed to predict the advance resistance focused on small cargo vessels, fi shing vessels and tugs, (Arbuniéz & Caja, 2015, p. 34).
Th e analysis shows that for a speed of 11 Kn there is a total resistance of 117.1 KN and an estimated power of 1124.373KW which are the starting point for power prediction.
Based on the data obtained, referring to the advance resistance and calculation of the optimum propeller for the vessel being designed, the vessel in the project will have two axle lines with one power in each engine: BHP: 592 KW

Advance resistance
Powering Th e selected engine is a Diesel MTU 12V-M61, which compared to the other engines observed in the table has a fuel consumption g/h which equals a better performance, and the dimensions show that it is smaller than the other two engines shown in the data table.Th e engine is from the German company MTU with a power of 1184 Kw equivalent to 1610 HP.
According to the chosen engine manual, by recommendation it is compatible with the ZF 5000 NR2H gearbox with a 2.963 ratio, which does not require a special manufacturing order.
Th e design of this vessel requires that the propulsion system has a 4-blade propeller.To avoid torsional vibrations and synchronisms induced by axial thrust of the blades, kort type nozzles are implemented for each propeller, which decreases the vibration induced in the hull by the propeller, since it provides a greater regularity of the fl ow inside, reducing the fl uctuations generated by the propulsion engine.It also provides protection to the fl ow of water aff ected by the propeller and therefore decreases pressure variations on the hull around the propeller.Th ese nozzles are designed to increase the traction force of the tug at low speeds.
Th e tug must have the following navigation and communications equipment GMDSS A1 (Global Maritime Distress and Safety System) is a SOLAS and IMO convention, an international agreement on safety procedures, types of equipment and communications protocol to enhance maritime safety, divided into 4 maritime zones.Th e ship design will use zone a1 which is between 20 -30 MN from the coast.
• TR-20   Conceptual design of a 20 TBP port tugboat for the "Bahía Málaga" ARC Naval Base • For indoor communications, command telegraph equipment shall be mounted on a transmitter and two receivers, a maneuvering loudspeaker system with 2 repeaters on the main deck and the bridge.
The tugboat will need the basics for its operation and therefore the following auxiliary equipment must be installed: • Two starting air compressors from 14 m3/h to 30 bar. • One emergency starting air compressor from 9 m 3 /h to 30 bar • Pressurized air dryer filters • One petrol purifier with a capacity of 1500 l/h • One electric centrifugal pump of 40 m 3 /h at 3 bar for fresh cooling water service, as backup for the main engine.• Two centrifugal electric pumps of 70 m 3 /h at 3 bar, for the salt water pump of the main engine.• One electric centrifugal pump of 15 m 3 /h at 3 bar, for transferring fresh water within the ship.• Two centrifugal electric pumps of 25 m 3 /h at 4 bar and 40 m 3 /ha 1,5 bar, for flushing, firefighting, ballast and bilge pumping.• One electric helical pump of 5 m 3 /h at 1,5 bar, for oily waters.• One self-suction electric pump with a 15 m 3 /h screw at 2 bar, for fuel transfer.• One 2.5 m 3 /h at 5 bar self-suction screw electric pump for the main engine fuel reserve service.• One 35 m 3 /h at 10 bar self-suction screw electric pump for the main engine reserve oil lubrication service.• One electric centrifugal pump of 1 m 3 /h at 2 bar, for waste water discharge.• One electric centrifugal pump of 20 m 3 /h at 2,5 bar, for salt water cooling of the air conditioning equipment.• One salt water hydrophore, consisting of a pump of 2 m 3 /h at 3 bar, with a 50 l capacity tank.
• One fresh water hydrophore composed of a pump of 4 m 3 /h at 3 bar, with a 50 l.capacity tank.• One bilge separator with a 1 m3/h capacity.
• One biological waste water treatment plant, which receives by gravity and treats waste water for 4 people on board.• Two axial and reversible fans with a flow of 25000 m3/h each, for the ventilation of the machine room.• One centrifugal fan with a capacity of 2000 m 3 /h for the engine service room.
The ship shall have enough space to accommodate a crew of 4 persons consisting of: • Under the main deck two double cabins equipped with bunk beds, wardrobe and desk, bathroom with shower, toilet and washbasin, washing machine and dryer for crew, living room for 4 people, stainless steel kitchen, food pantry room, with a freezer inside, a longitudinal corridor from stern to bow will connect the engine room with a hatch entrance and exit, then with cabins on each side, along the corridor there will be communication with the bridge on the main deck that will have a hatch to exit the bridge, interior doors will be galvanized steel with PVC or stainless steel, acoustic insulation and thermal insulation for high noise reduction and fire resistant.
The structural study of a ship can be carried out by considering it as a beam ship in which the shear and flexural stress to which the ship is subjected in a specific condition are studied, for the calculation of these stresses the most drastic conditions must be taken into account.
The American Bureau of Shipping (ABS), part 3, guide for building and classing will be used for the analysis.

Auxiliary Systems
Outfit and Furnishings

Royet del Gallego, Orozco
For this project, which is defi ned as a Conceptual Design, a breakdown will be made of the main structural elements of the vessel "20 TBP Port Tug for the National Navy", the frames, web frames, longitudinal and transverse bulkheads.Vessels of this type have mainly, a transverse structure with special reinforcements in the keel area, the propellers and especially in the bulwark, an area that can be especially subject to blows during operations.
In order to carry out the electrical balance, the loading conditions in port, navigation, maneuvering and emergency have been studied.From this study, the power in KW required for the power plant was obtained.Th is consists of two main Caterpillar generators, model C4.4 of the following technical characteristics: 100kW, 125 kVA, 220VAC, 320Amp, power factor 0.8, 1800 RPM and an emergency Caterpillar generator C4.4 Model ACERT 4.4 three phase, 36kW, 120V 240V, 60 HZ, 1800 rpm.Th e main generators will be located in the machine room on both sides, connected to the main board.Th e emergency  Conceptual design of a 20 TBP port tugboat for the "Bahía Málaga" ARC Naval Base engine generator will be located in a separate compartment for that system only.

Estimate of electricity generation system
The diesel engine of the emergency generator will be started by means of an electric engine and battery, connected by means of a low voltage contactor to the emergency bars in the panel.
The cost estimate for this tugboat design was made in a general way, in order to obtain a conceptual estimate of the costs for construction.
The calculation of estimated costs is calculated without considering the "other" expenses that may result, where only the hull, structure, material, costs of shipyard, equipment, machinery and facilities were estimated.
For the estimation calculations the approximation established by (Carreyette, 1977, p 245) is used, in which you can estimate the price of a ship, considering the following characteristics for a tugboat: Finally, an estimation of the shipyard costs is made, which includes services, materials, tools, equipment, machinery, among other elements.Also, the estimation of the general expenses is made, which are included and are characterized by carrying a % of expense similar to 30% of total cost in man hours.It is also estimated that the construction profit is 5%.
In principle, the estimated cost of building the port tugboat would be $2,011'975,000 Colombian pesos.
In this investigation, the proposed objectives were met.
A conceptual design was achieved, fulfilling each of the proposed objectives, concerning port tugboat for the National Navy, having the necessary capabilities to support the vessels of the entire naval fleet.It is of great importance that the design of a vessel of this type can be developed into its construction, considering the institutional plan of the National Navy of compliance, plan 2030.
The design and context of this project is achieved with the help of computer tools, being able to design the hull shapes in the Maxsurf software, maintaining the main characteristics, determining a reliable analysis.It was also possible to analyze and evaluate the type of propulsion, propellers and generators to be selected.
For the propulsion system, the installation of two 1610hp MTU propellers, two lines of axles with 4 blades propeller, a diameter of 67.29in, were considered, thus meeting the power requirement to overcome the advance resistance of these vessels.
The design focused on the calculation of the advance resistance, and weight capacities, all analyzed and determined with the computational tools.

References
Finally, an approximate cost estimate was determined, considering the conceptual analysis up to its construction and launching, analyzing each possible cost, dividing the construction by construction groups and taking an organization with reference in the design and construction methodology.The total cost estimate for this tugboat was $2.011´975.000projected for construction in 2020.
To carry out the development of this project requires great knowledge in computational tools focused on design and engineering analysis, focused on the naval issue.In addition, it must have a permanent company of teachers, naval engineers and the shipyard's own engineers, in this case, Cotecmar.

Table 3 .
Engine Comparison

Table 6 .
Characteristics of the 20 PBS tugboat