Page 194 - Pipelines and Risers

Trawl Irnpaci, Pullover and Hooking Loads 167

B= the half-height of the trawl board

For trawl boards a maximum vertical force acting in the downward direction can be accounted
for as
Fz = F, (0.2 + 0.8e-25z) for polyvalent and rectangular boards (11.23)
F, = 05F, for v-shaped boards (11.24)

The total pullover time, T, is given by
T, =CTCF(m/k)“2 +6, IV (11.25)

where:
6, =0.1(~,~,(m/k)”~) (11.26)
CT is the coefficient for the pullover duration given as:
CT= 2.0 (for trawl boards)

The fall time for the trawl boards may be taken as 0.6 seconds, unless the total pullover time
is less than this, in which case the fall time should be equal to the total time.
Figure 11.3 shows typical time history of vertical forces and horizontal forces.

2.6
2.4
3.0
2.8
2.2
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 +
‘-v-’ flME(SEC)
0.6 SEC 0.6 SEC
Figure 11.3 Mover Load - Time .I History