Mooring Loads Due to Parallel Passing Ships - State Lands ...

In addition, significant work was required to design and construct a mooring rig
that would allow surge and sway forces, as well as yaw moments, to be measured on a
moored ship model. This measurement rig was designed and constructed concurrent
with the development of the towing rig. In fact, two test rigs were developed.
The first test rig was constructed using a heavy aluminum frame and is shown in
Figures 4 and 5. With this rig, square modular force blocks were mounted in the ship
model and were attached to the aluminum frame using vertical guide rails running
through roller bearings fore and aft. These restrained the model in surge, sway, and
yaw while allowing heave and pitch motions. Surge and Sway forces were measured
at both the fore and aft gage locations.
While this test rig was used successfully in one test series (tests using one
water depth of 4.9 inches), it proved troublesome and was eventually replaced.
Problems arose due to occasional binding of the vertical rollers and due to use of the
modular force blocks. These force blocks had 5 and 10 pound capacities and had
difficulty resolving the small loads being experienced, which were sometimes on the
order of 0.01 pounds.
Figure 4. Original test frame used to measure mooring loads, viewed from top
NFESC TR-6056-OCN
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