In
this example the earlier discussed theory will be used, for a real anchor at
a certain depth, to check the different forces on this anchor.
First of all the
vertical and horizontal forces ‘created’ by the fluke will be determined,
the results of these different forces are shown in the figures below
Vertical fluke force 3D
Horizontal fluke
force 3D
For this situation the α = 0,15 (for example) β = 0,3.
So:
Fv =
5570N
Fh =
3470N
Now the forces
perpendicular to the shank will be calculated for the case that:
B= 0,1m
y=
γ= 1900
kg/m3
Φ= 0,611 rad
= 1280N
After this, the
friction force of the shank will be determined to be:
= 4000Pa
= 0.6m
Forces on
the anchor
When looking at the point where the anchor becomes stable a force and moment
balance can be made out of all the forces on the anchor and mooring line. In
fact this is the moment were the anchor reaches his maximum holding capacity.
Vertical equilibrium of forces:
Now one can
calculate the maximum vertical component of the pull force Tv :
The maximum
horizontal component of the pull force (Th) can be calculated in the
same way:
Moment balance to point A:
Maximum pull force vs. depth
In practice:
When positioning an anchor, at each anchor position the maximum pull force can
be determined.
For the next
point this process will be repeated and the maximum pull force at that specific
position can be calculated as well. As a result of these positions, a curve can
be made of the holding capacity of the anchor at a certain depth.