A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Mooring dolphins, as the name implies, are used for mooring only and for
securing the vessels by using ropes. They are also commonly used near
pier structures to control the transverse movement of berthing vessels.
Fig. Breasting dolphin and mooring dolphin
8. Should dolphins be designed in a rigid manner, i.e. resting on
several raking piles?
In designing dolphins, they are normally supported on a system of three to
four raking piles. This in essence is a rigid structure and exhibits little
flexibility e.g. movement against impact and berthing loads by vessels. In
fact, this kind of design may not be desirable in terms of maintenance
because the dolphins are readily susceptible to damage by high berthing
vessels. To rectify this situation, some energy absorption devices like
rubber/plastic fenders have to be installed to reduce the impact load
deriving from its own deflection. On the other hand, by designing dolphins
as flexible structures capable for allowing slight deflection, it helps to
reduce the large forces generated during berthing of vessels. In this
connection, one way of designing dolphins as flexible structures is by
provision of a single pile only.
Note: For a rigid structure, it takes up external loads without undergoing excessive
deformations.
9. Why is sulphate-resisting cement not used in marine concrete?
The main components of Portland cement are tricalcium silicate, dicalcium
silicate, tricalcium aluminate and tetracalcium aluminoferrite. In
sulphate-resisting cement, it contains a low amount of tricalcium aluminate
in order to avoid sulphate attack. Otherwise, tricalcium aluminate would
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