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Following and Quartering Sea (2/2) - Coggle Diagram
Following and Quartering Sea (2/2)
Semistatic Case
Only for Small and Fast Ships
In long waves
\( \dfrac{L_w}{L} \geq 1,0 \)
Alternatively
Can reach this condition
if calm-water speed
exceeds Fr of 0,25 \( \dfrac{V}{ \sqrt{L} }=0,84 \)
DuCane and Goodrich
Model tests
1,25 < Lw/L < 2,4
Model accelerated by waves
above calm-water speed
SURF
Heading deviation - Wahab and Swaan
Greater if bow in trough
more unstable
Smaller if bow in crest
No matter how stable
is in calm water
Lw/L > 1,5
Becomes unstable
Unstable in calm waters
might become stable
long waves, bow in crest
Wahab and Swaan Conclusions
Great danger of broaching
even with controls working
Bow in trough
wave length >=
1,5L
Likelihood of broaching
Increases with wave height
Reduction in danger of broaching
can be achieved
by increase in fin area aft
improving smooth water controls-fixed
Autopilot
can reduce regions of instability
Use of Rudder
Encounter frequency low
yaw motion is large
Angles BTW 15 and 30° of following sea
Improves stability
Increase Rudder Size
unless at high frequency encounter
low speeds
