HULL REDESIGN AND ITS EFFECT ON THE RESISTANCE OF MANADO PROTOTYPE SMALL PURSE SEINER

This research aims to determine the effect of redesigning the hull of a small purse seine ship on its motion resistance. The research was carried out using a small purse seine ship prototype in Manado by changing the length-breadth-depth ratio based on the ship's main dimensions, resulting in three new hull designs coded K-0 (prototype), K-1, K-2, and K-3. Maxsurf modeler and Maxsurf resistance were used to run a simulation set of three loading conditions (light, half, full) and speed (low, medium, high). The research results show that changes in ship hull design affect the resistance and thrust of the ship. There is a difference in resistance between the ship with the redesigned hull and the prototype, where K-3 shows the smallest difference. In addition to changes in hull design, changes in ship loading conditions, Froude number, and ship speed lead to increased ship resistance and thrust. Based on the average allowance (sea margin or service margin) in shipping lanes, the need for propulsion power and the number of propulsion power vessels K-0 (prototype) and K-3 are still better than K-1 and K-2.


INTRODUCTION
Ships are a means of transportation to bring goods and or passengers from one locality to another on the water and are built according to their respective interests (Suriadin and Putra 2021).Fishing boats, fishing gear, and fishermen are three factors supporting the success of a fishing operation (Soeboer et al. 2018).Fishing vessels in Indonesia have a variety of shapes (Putra et al. 2020).The vessel shape is significantly affected by fishing grounds and operations (Niam and Hasanudin 2017).
Purse-seiners are fishing vessels widely used by fishermen in small pelagic fishing activities.According to Azis et al. (2017), purse seiners belong to a type of fishing vessel targeting the schooling fish by encircling the fish schools.They have a variety of distinctive shapes with the locality where the ships are made.Despite their different shapes, they all intend to support the ship's activities in operating purse seines.Indonesian fishing boats, including purse-seiner, are made of wood, have a relatively small size, under 25 m long, and are generally planned and made traditionally (Mulyanto et al. 2019), with an easier and simpler manufacturing procedure than steel vessels (Liu et al. 2019;Chrismianto et al. 2020).
Purse seine fisheries in North Sulawesi Province are located in several different localities, including Bitung, Molibagu, Belang, and Manado, each with its typical shape and different technical capability.A previous study (Pamikiran et al. 2017) found that the purse seine vessel of Manado has a better technical capability than other areas.Based on this study, the original type of Manado purse-seiner has a better resistance value than vessels from other purse seine fisheries-based areas in North Sulawesi.Nevertheless, the hull line needs to be redesigned in relation to the ship capacity development, particularly the ship resistance, and power.
The ratio of length (L), width (B), and depth (D) are a significant component that will indirectly provide an idea of the ship's shape and influence its performance, such as resistance, stability, loading ability, and motion.It is in agreement with Putra et al. (2020) that different ship shapes will give different technical capabilities of the ship, such as resistance, movements, and stability.Ship resistance is a fluid force that acts on a ship in such a way that counteracts the movement of a ship in which the resistance is equal to the component of the fluid force acting parallel to the axis of the ship's motion (Harvald 1992).In general, ships moving in the water at a certain speed will experience resistance forces opposite to their direction.This resistance must be overcome by the thrust of the ship's propulsor.Information on the ship's resistance is essential in relation to the ship's speed and propulsion, which will affect the propulsion engine's thrust needs and fuel oil use.The interaction between the ship resistance and velocity needs to be balanced to make use of power efficiency (Diaz-Ojeda et al. 2023).There are several definitions of power often used in estimating the power requirements of the ship propulsion systems, including adequate power, i.e., the amount of power needed to overcome the inhibitory force of the ship's body (hull) so that the ship can move from one place to another at the service speed (Vs).Thrust is the amount of power generated by the work of the ship's propulsor to push the ship's body.
For the average condition of sailing service, an additional leeway should be given on the resistance and effective force caused by wind, erosion, and fouling of the ship's body.The addition of this leeway depends mainly on the cruise line.The average allowance for resistance or planned effectiveness for East Asian shipping lines is 15-20% (Harvald 1992).It means that designing the ship's effective power requires an addition of 15-20% to avoid power deficiency in poor weather conditions.This study is aimed at knowing the resistance of the redesigned vessel, including the prototype as basic information to set the ship power added with the service margin.

METHODS
The redesign and data analysis were carried out in the drawing room of the Shipmenship Laboratory, Fisheries Resources Utilization Study Program, the Faculty of Fisheries and Marine Sciences, Sam Ratulangi University, Manado.This study was carried out from July 2019 to January 2020.

Research procedure
Data collection covered the technical data of the prototype ship in the form of the size and hull line of the ship from Manado City (Pamikiran et al. 2017).The prototype ship is the original purse seiner of Manado, which has better technical capability than the ships from other areas.This ship shape was adopted as a standard measure.
The redesign of the Manado prototype ship in the form of a hull line was carried out by changing the ratio of breadth (B) and depth (D) of the ship.The change in the ratio between the principle dimensions of Length (L), Breadth (B), and Depth (D) is carried out based on the standard ratio of the principle dimensions of purse-seiner proposed by Fyson (1985) as follows: L/B = 3.10 -4.30, B/D = 2.10 -5.00, and L/D = 9.50 -11.00.From the middle value of the scale of the primary size, three new hull line forms were obtained, and together with the prototype ship, the following abbreviation codes were given: K-0 (prototype), K-1, K-2, and K-3.The redesign was conducted by altering the ratio scale of the primary dimension; namely, the hull-line structure was altered in two directions, the width and the height, whereas the ship length did not change.The change in hull-line structure was done automatically through transform scale vector and simulation of transverse axis and vertical axis values, while the longitudinal axis value was maintained.Thus, this redesigning only alters the ratio of the principle dimension and the hull-line structure, whereas the block coefficient (Cb) and prismatic coefficient Cp) remain the same; the change only occurs when the submerged part changes from loading conditions (I=light condition, II=half condition, and III=full condition) (Table 1).The implementation of the draft values on three immersion conditions of the ship operation were 13% for light condition, mid-draft (half-submerged), and 18% from the half-draft to the full-load condition.The ship's offset body plan data, buttock line data, and hull-line image are presented in Tables 2 -5 and Figures 1 -4.

Data Analysis
The hull line data were inputted into the free-ship plus application.The data format was then adjusted to the application by exporting the data from free-ship plus and importing them into the Maxsurf Modeler Advanced application.This application changed the hull line data format to a format corresponding to the Maxsurf Resistance Enterprise.Maxsurf application, including Maxsurf Resistance, was also used for data analysis by taking advantage of free Maxsurf Enterprise V8i (SELECTSeries 3) 20.00.02.31.The Froude number was used to obtain the value of ship speed in various categories, namely low, medium, and high speeds, using the formula below (Harvald 1992): where V is ship speed (m/s.), g is the acceleration of gravity (9.8 m/sec 2 ), and L is ship length (m).
In this study, the calculation of ship resistance used the Wyman method.The ship's total resistance data consisted of friction, auxiliary, air, and residual resistance.The friction resistance and coefficient were calculated following the formulation of the International Towing Tank Conference (ITTC) 1957.The formulations used in the analysis are as follows: where ABT is bulb area because the fish boat does not have a bulbous bow, then ABT = 0, B is the breadth, Cb is block coefficient, Cf is the frictional coefficient, Cm is midship coefficient, Cp is the prismatic coefficient, Cw is water area coefficient, LWL is the length of waterline (m), Rf is total frictional resistance (N), S is wet surface area of the vessel (m 2 ), T is draft (m), V is ship speed (m/s), ρ is density of seawater (1.025 kg/m 3 ), and ν is kinematic viscosity of seawater 0.94252 x 10 -6 m 2 /s (at the temperature of 25 o C).
Additional ship resistance (RAPP) is determined based on additional part factors (1 + k2), which is determined by the following formulation: (1 + k2) =  E2 /  E1 ............................. (10) where  E1 is the value of the presence or absence of additional parts and  E2 is the multiplication of the value of the presence or absence of additional parts and the value of the factor: R APP = (1 + k2) x Cf x 0.5 x  x As x V .... (11) where CF is the coefficient of friction, 1 + k2 is additional part factor values,  is seawater density, 1025 kg/m3, As is the area of additional fields, and V is variation in ship speed in m/s.
The power needed to respond to the ship's resistance to various speeds was obtained by converting the ship resistance value in Newton's (N) unit to the horsepower (HP).The conversion was calculated as follows: HP = Rf (N) x V (m/s) Where 1 N. m/s = 0.001 kW, and 1 kW = 1.34102HP.

RESULTS
Based on the redesign of K-1, the dimension needed to add the ship breadth and depth, the K-2 ship only needed to add the depth size, and the K-3 ship needed to add the width size, whereas the prototype ship of K-0 (prototype) did not change.This condition causes the hull-line structure change, influencing the ship submergence, wet surface area, and half angle of entrance (Table 6).
The relationship between the Froude Number and the ship's resistance, as well as the ship's speed and power in three load conditions, namely light condition (I), half condition (II), and full condition (III), are presented in the form of a two-dimensional curve .The changes after the redesign and the submerge condition applications (Table 2) could be the reason for the highest resistance and power of the K-1 and the lowest resistance of the K-0 compared with those of K-2 and K-3.The addition of the ship draft (K-1 and K-2), submersion (K-1, K-2, and K3), and half angle of entrance highly influenced the ship's resistance and power.The resistance and power values of K-0 and K-3 are not significantly different, but these are different from those of K-1 and K-2.In general, it could result from the difference and addition of displacement value, wet surface area, and half angle of entrance.However, there is a privilege and advantage of the K-3 ship; even though this ship has a larger wet surface area and half entrance angle than the K-2, the K-3 has lower resistance value and power.
The estimated power values of the four ships at full condition and high speed (V3) are presented in Table 7.If the mean looseness of the sea margin (service margin) for adequate power is considered (Harvald 1992), then the propulsion required will be 90.54HP for the ship K-0, 135.99 HP for the ship K-1, 116.53 for K-2, and 105.66 HP for K-3, respectively.In the field, prototype ships usually use four outboard motor units with a power of 40 HP for each outboard motor, meaning that the total driving power is 160 HP.The amount of propulsion required for the service margin of the K-3 ship is very close to that of K-0, only 16.70% (15.12 HP), whereas that of K-1 and K-2 have higher service margins.Based on the ship resistance, power, and power needs to meet the margin service, the K-0 and K-3 ships tend to be similar.However, K-3 has a larger loading capacity than K-0 (prototype) because of the breadth and the rise in submergence, as shown in Tables 1 and 6.In addition, K-3 also has better stability than the previous finding (Pamikiran et al. 2020).

CONCLUSION
Redesigning the Manado prototype purse seiner has altered the ship's hull-line structure onto the transverse and vertical axes by maintaining the longitudinal axis.
Changes in the ship's impact from light conditions, half condition, and full load, as well as changes in Froude numbers and ship speed, led to an increase in the ship's resistance and thrust values.Changes in the shape of the hull line caused changes in the value of the ship's resistance and thrust, in which, based on the average allowance (sea margin or service margin) on the ship's shipping lane, the need for propulsion and the use of the amount of propulsion for K-0 ships (prototypes) and K-3 ships is still better than that of K-1 ships and K-2 ships.Besides, the K-3 ship has a higher capability in shipping services.

SUGGESTIONS
The findings have shown that the K-3 ship design yields higher resistance than the prototype, but the percent service margin was lower than the allowable sea margin added for sea safety.The redesigned K-3 ship has a more extensive hull line than the prototypes, which helps increase the ship's stability on the water.Therefore, the redesigned hull line of the K-3 purse seine vessel could be considered for small purse seiners in Manado and North Sulawesi.A safe range of hull line development is also crucial to be established.Nevertheless, further studies are needed to carefully decide on a possible ship design development for other purposes.

Figure 5
Figure 5 Froude number curve and ship resistance on light condition (I) for prototype and redesign of Manado small purse seiner, Indonesia.

Figure 6
Figure 6 Speed curve and ship power on light conditions (I) for prototype and redesign of Manado small purse seiner, Indonesia.

Figure 10
Figure 10 Speed curve and propulsion of the ship on full conditions (III) for prototype and redesign of Manado small purse seiner, Indonesia.

Table 1
Principle dimension, draft, Cb, and Cp in various loading conditions.

Table 3
Body plan and buttock line offset data of K-1 (first redesign of Manado small purse seiner prototype, Indonesia) Where: ST (Station), WL (Water Line), and BL (Buttock

Table 4
Body plan and buttock line offset data of K-2 (second redesign of Manado small purse seiner prototype, Indonesia)

Table 4
Body plan and buttock line offset data of K-2 (second redesign of Manado small purse seiner prototype, Indonesia) (continued) Where: ST (Station), WL (Water Line), and BL (Buttock

Table 5
Body plan and Buttock Line offset data of K-3 (third redesign of Manado small purse seiner prototype, Indonesia)Where: ST (Station), WL (Water Line), and BL (Buttock