Pacientes con infección por VIH en las Unidades de Cuidados

In a narrow channel or confined area, vessel movements can occur in the same direction, opposite direction or at an angle (viz. 90º between vessels). The safe distance between two queuing ships in a port area depends on the ships’ sizes, that is; (i) 1

nautical mile (nm) in between (over 20,000 g.r.t), (ii) 0.5 nm in between (500 g.r.t ~

Safety barrier(xi) Failure probability P(xi) General skill requirement (GSR) 2.90×10-3

Management training requirement (MTR) 4.21×10-2 Technical knowledge requirement (TKR) 5.27×10-2 Emergency skill requirement (ESR) 2.71×10-2 Sailing experience requirement (SER) 10.88×10-2

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20,000 g.r.t), and (iii) 4 times a ship’s length for ships under 500 g.r.t (Hsu, 2014).

According to IMO (Nautical-Institute, 2013), the safe distance (Figure 4–8) to comply with collision regulations is as follows:

• Port side of any route: 6 ship lengths + 500 m

115 6 ship lengths 500 m Far Approach Port Starboard 6 ship lengths 500 m 0.3 nm D = 1 nm D = 1 .5 nm

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For example, two vessels are heading in the same direction (Figure 4–9) in the port area, and the distance between them is about 3000 m. If the host vessel is 160 m in length, then the required safe distance to manoeuvre is on port side, (6 × 160) + 500 = 1460 m and on starboard side, 0.3 nm (555.6 m) + (6 × 160) + 500 = 2015.6 m. However, 1 nm (1852 m) is recommended by the port traffic control for vessels moving in a line, under same speed forward, and with similar headings (Hsu, 2014). So, the remaining distance before the minimum safe distance starts is 3000 – 1852 =1148 m. The proposed collision alert system will use the hull sensor to check the safe distance frequently and hence alert the shipmaster in real-time. If the total distance between vessels, D = 3000 m and safe distance for vessels moving in a line, under same speed forward, and with similar headings, dsafe = 1852 m then remaining distance, dmin = 1148

m. It can be expressed as, D = dmin + dsafe. The remaining distance, dmin can be divided

117 D = 3 0 0 0 m dm in = 1 1 4 8 m ds a fe = 1 8 5 2 m (1 n a u ti ca l mi le ) Sa fe d is ta n c e 1st warning

Action: Situation Assessment

x1 = ¼ x dmin = 287 m

2nd

warning

Action: Appropriate Action x2 = ½ x dmin = 574 m

3rd

warning Action: Immediate Action

x3 = ¾ x dmin = 861 m 4th

warning Action: Evasive action

x4 = 1 x dmin = 1148 m

Very far Far Close Very close

Warning (sound and display on monitor) A C B Time (t) t + Δt t + 2Δt t + 3Δt A. Situation assessment B. Appropriate action C. Immediate action D. Evasive action D

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The “Warning” node has five states, (i) first alarm, (ii) second alarm, (iii) third alarm,

(iv) final alarm, and (v) no alarm. It is assumed that the host vessel is approaching at medium speed with reasonable manoeuvrability. The likelihood of first alarm is increased when the host vessel embraces one-fourth of dmin which is considered as very

far. The second alarm is activated when the vessel crosses half of dmin which distance

is considered as far, and the third alarm is activated when vessel crosses one-third of

dmin which is considered as close. The final alarm is activated when vessel crosses dmin

which is considered as very close and requires evasive action. No alarm is kept as an option, when the risk is extremely low. The shipmaster is therefore being notified through the different states of the alarm to keep the minimum safe distance on the port, starboard and bow side.

The four “Decision making” nodes are dependent on “Warning”, and Decision-making

skills (GSR, MTR, TKR, ESR and SER). In an emergency, the decision of a shipmaster is critical. The “Warning” node is dependent on “Navigational state”, “Weather and environment state”, “Own vessel speed”, “Target vessel distance”, and “Own vessel manoeuvrability”. The “Own vessel manoeuvrability” node is dependent on “Target vessel type”, “Target vessel length (m)”, and “Target vessel speed”. The input node “Target vessel distance” has four states: very far, far, close and very close. Similarly, “Own vessel speed” and “Target vessel speed” have three states: low, medium and high. “Target vessel type” has four states: cargo, tanker, passenger and fishing and “Own vessel manoeuvrability” has three states as reasonable, tight and extremely tight.

The outputs of preceding OOBNs (e.g., human factor state, navigational and manoeuvring state, visibility state and environment state), as well as other nodes (e.g.,

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own vessel speed, target vessel distance, and own vessel manoeuvrability), are taken into consideration in the proposed model (Figure 4–10).

Gen eral skill requ irement (GSR)

Manag ement training requ irement (MTR)

Technical kno wle dge requ irement (TKR)

Sail ing exp erience requ irement (SER)

Naviga tional and manoeuvring sta te

Immed iate acti on

Emerge ncy skill requ irement (ESR)

Visibility stat e Weather a nd environment stat e Environment stat e Hum an fa ctor state

Situation assessment

App ropriate

acti on Evasive action

Naviga tional

stat e Warning

Own ve ssel manoe uvr ability

Target vessel distance Own ve ssel speed Target vessel speed Target vessel leng th (m) Target vessel type

Figure 4–10: OOBN model for the confined area.

The model in Figure 4–10 explicitly combines all the preceding OOBNs to form a larger model for collision alert and decision making at a different stage of vessel navigation from a very far distance to very close distance.