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20 H. AKYILDIZ ve E. TÜRKMEN

Table 1. Risk Analysis of ASV by adopting FMEA methodology

Fault End Effect Consequences Severity Level
Δn>0 Decreased boat speed Very High
Maneuvering risk, high energy
consumption, operation cancel

Δn<0 Acceleration Maneuvering risk, high energy Very High
consumption, operation cancel,

collision risk

ΔX>0 Decreased or reversed Maneuvering risk, high energy High
boat speed consumption, operation cancel

ΔX<0 Increased boat speed Maneuvering risk, high energy High
consumption, operation cancel,

collision risk

ΔI>0 Decreased or reversed Maneuvering risk, high energy Very High
boat speed consumption, operation cancel Very High

ΔI<0 Increased boat speed Maneuvering risk, high energy
consumption, operation cancel,

collision risk

• A first class faults are regards to shaft speed measurement which is performed by
tachometer.

Δn = nref – n (rpm)

If Δn is positive, it means there could be some problems at motor controller, the control system
or the thruster. It leads to decrease of boat speed. If problem is at the thrusters there is not so much
solution to repair because the mechanical system fault. On the other hand, if problem at the motor
controller or the control system some solutions could found such as filtering software or the
auxiliary systems against a fault. However, if Δn is negative, it means that there could be some
problems at motor controller or control system. It leads to increase of boat speed.

• The second class faults are related the position values which is performed by the GPS.

Δx = xref – x (u,v,w)

If Δx is positive, it means there could be some problems at a control unit, motor controller, the
thruster or the GPS. It leads to decrease of boat speed. Although, probability of occurrence of
obtaining faults at GPS, if some faults occurs on this part, repairing of part will be impossible

GiDB|DERGi Sayı 5, 2016