Analysis of deck house height and center of gravity in anti-capsize patrol boat

The design of patrol boats, especially in Indonesian waters which have extreme sea conditions, requires fairly good stability capabilities and special self-righting capabilities. Designing a self-righting ship will be closely related to the ship stability because the center of gravity (G) is affected by the load and the height of the deckhouse of a ship, which has implications for the ship’s self-righting. Present study was carried out with experimental study for patrol boat design that has capability self-righting moment. The patroal boat has 4 deckhouse height variations with 2.01 m, 2.11 m, 2.21 m, and 2.31 m, respectively. There are 4 variations of the load conditions, i.e., the condition with 50% of the maximum amount of cargo, the condition 50% the passengers and cargo, full load condition without passengers, and the last one is the condition of the passenger baggage is only 50%. The results showed that a deckhouse with a height of 2.01 m has the worst GZ curve analysis, where in some conditions the results touch a negative number before heeling to 180°. The results showed by trial and error that the minimum deckhouse height is 2.07 m to have a self-righting moment in all conditions.


Introduction
The self-righting moment is a concept where the ship can return to its upright position after being upside down to a certain degree or even completely upside down (180°) without the help of an external force.The previous study of a patrol boat with an effective self-righting moment was performed using experimental and numerical methods [1,2].The results showed that the numerical method has the same phenomenon as the experiment: the ship has self-righting in all condition load cases.Numerical methods such as CFD have become famous for marine use, such as fast ship design [3,4] and ship performance [5,6].Another CFD scheme such as mesh-free CFD, i.e., smoothed particle hydrodynamics (SPH) that is suitable for marine engineering cases such as water wave propagation [7,8] and sloshing in LNG cases [9][10][11].Designing a self-righting ship will closely affect the boat's stability because the load affects the centre of gravity (G).The height of the superstructure of a vessel has implications for the ship's self-righting conducted by Bai et al. [12] shows that the height of the centre of gravity affects the ship's self-righting moment, where there is a graph of the righting lever which shows that the higher GZ (height of the centre of gravity), the ship's self-righting moment will decrease its ability.
According to previous research, the addition of the height of the superstructure on the ship influences the stability of the ship because there is also an increase in the volume of the superstructure, which will have an impact on increasing the volume of the part of the ship that is submerged in water when the vessel is tilted at a certain degree when water superstructure.This influence can be seen from the area of the stability arm curve (GZ curve), where the elevation of the superstructure affects the maximum GZ magnitude and the angle at which the maximum GZ [13].The present study is based on previous works [1], i.e., a patrol boat with four variations using different deckhouse heights where there are heights of 2.01 m to a height of 2.31 m with a difference of 0.1 m each.The analysis results showed that the condition of the ship with the lowest deckhouse height does not have an excellent self-righting IOP Publishing doi:10.1088/1755-1315/1298/1/012004 2 moment compared to the other variations, whereas in a fully loaded condition, a patrol boat with a deckhouse of 2.01 m has a negative moment at an angle at 17°.Meanwhile, ships with the highest deckhouse height at 2.04 m find the best self-righting moments.This research was continued by validating and simulating using Star-CCM+.Patrol boats with a height of 2.04 m are simulated with maximum load conditions, able to return to an upright position in 0.7 seconds and produce stability in 3 seconds.
This research focuses on the modification of the height of the deckhouse and finding out the minimum deckhouse height that has a self-righting moment.Finally, the results showed that the minimum deckhouse height was found to be more than 2.0 m.

Ship Model
The reference ship model based on MV Barracuda which was designed in previous studies [2].For the main dimension of the ship can be seen in Table 1 and for the three dimension model shows in Figure 1.
Table 1.Main Dimension Data (units in m) No Main Dimension Dimension

Deckhouse Variable
The reference variations for deckhouse heights were based on previous studies where four types of deckhouse patrol boats were used.The variations in the height of the deckhouse are illustrated in Figure 2, in which the change is 5%, 10% and 15% from the base model deckhouse height, so each model has an additional height of 0.1 m.
Therefore, the authors made variations in the weight of the component into four conditions by changing the percentage of the weight of the DWT component.
The four conditions are: a.The ship's condition with 50% cargo weight, 0% passenger baggage, and 100% passengers totalling six people.b. 50% total passengers with 0% passenger baggage and 50% cargo.c.Only 50% of all passenger baggage.d. 100% load, no passengers.The analysis was carried out using the Maxsurf software to determine the GZ curve or stability calculation of moment koppel.

The Calculation of GZ curve
The load loading test was carried out out in 4 conditions with LWT data for four ship models as follows.Load case 1 is where each cargo weighs 50% of all and the condition of no passenger baggage but 100% of passengers.The results show that each variation of the ship's deckhouse has good stability, and no ship models touch the negative GZ to a 180° angle.This condition indicates that each ship model has a self-righting moment, therefore, the ship has a positive GZ curve (see Figure 3 (a)).
Load case 2 is a condition where the weight reduction is 50% of passengers, and the remaining cargo is 100%.The analysis shows that all deckhouses except deckhouse one experience good self-righting moments.Deckhouse 1 failed to return to the upright position at a heel angle of 170°, furthermore, deckhouse 1 has a negative GZ curve in this load condition (see Figure 3 (b)).
Load case 3 is a condition where the ship has three passengers who are placed on one side of the ship's passenger section, but the other side is left empty and also, for cargo conditions, is 50% of the total weight of the overall cargo.The analysis showed that each variation of the ship's deckhouse has good stability, and no ship models touch the negative GZ to heel angle of 180°.This condition indicates that all deckhouse heights have a positive GZ curve.However, this condition is unbalanced because the passenger load is only on one side of the ship, so there is a shift in the centre of gravity on the transverse axis (see Figure 3 (c)).
Load case 4 is a condition where all cargo is 100% fully loaded, but there are no passengers.The analysis showed that Deckhouse 1 failed to return to its original position at an angle of 170°.In contrast, the other deckhouses had good self-righting moments (see Figure 3 (d)).Therefore, deckhouse 1 did not have a self-righting moment.The four conditions are: a.The ship's condition with 50% cargo weight, 0% passenger baggage, and 100% passengers totalling six people.b. 50% total passengers with 0% passenger baggage and 50% cargo.c.Only 50% of all passenger baggage.d. 100% load, no passengers.The analysis was carried out using the Maxsurf software to determine the GZ curve or stability calculation of moment koppel.

The Calculation of GZ curve
The load loading test was carried out out in 4 conditions with LWT data for four ship models as follows.Load case 1 is where each cargo weighs 50% of all and the condition of no passenger baggage but 100% of passengers.The results show that each variation of the ship's deckhouse has good stability, and no ship models touch the negative GZ to a 180° angle.This condition indicates that each ship model has a self-righting moment, therefore, the ship has a positive GZ curve (see Figure 3 (a)).
Load case 2 is a condition where the weight reduction is 50% of passengers, and the remaining cargo is 100%.The analysis shows that all deckhouses except deckhouse one experience good self-righting moments.Deckhouse 1 failed to return to the upright position at a heel angle of 170°, furthermore, deckhouse 1 has a negative GZ curve in this load condition (see Figure 3 (b)).
Load case 3 is a condition where the ship has three passengers who are placed on one side of the ship's passenger section, but the other side is left empty and also, for cargo conditions, is 50% of the total weight of the overall cargo.The analysis showed that each variation of the ship's deckhouse has good stability, and no ship models touch the negative GZ to heel angle of 180°.This condition indicates that all deckhouse heights have a positive GZ curve.However, this condition is unbalanced because the passenger load is only on one side of the ship, so there is a shift in the centre of gravity on the transverse axis (see Figure 3 (c)).
Load case 4 is a condition where all cargo is 100% fully loaded, but there are no passengers.The analysis showed that Deckhouse 1 failed to return to its original position at an angle of 170°.In contrast, the other deckhouses had good self-righting moments (see Figure 3 (d)).Therefore, deckhouse 1 did not have a self-righting moment.

Figure 1 .
Figure 1.Three dimension of ship model authors made variations in the weight of the component into four conditions by changing the percentage of the weight of the DWT component.

Figure 3 .
Figure 3. GZ curve for all loadcase condition4.ConclusionIt was found the self-righting moment has linierly effect on deckhouse of patrol boat, nevertheless based on variations of deck-house in this study conclusions could be drawn as follows:a.The distribution of cargo loads on patrol boats have significant influences to the stability of patrol boats.DWT distribution, especially for small ships, needs to be symmetrical as results ship have self-righting cabilities.b.The minimum deckhouse height is 2.07 m with a ratio between the height and width of the ship of 4.2 m, the result is 1 m: 1,415 m.

Table 3 .
LWT and CoG Data of Patrol Ship

Table 3 .
LWT and CoG Data of Patrol Ship