Page 72 - Practical Ship Design

Setting Design Requirements 43

2.5.8 Explorationldrilling rigs

Most exploration work has been carried out by jack-up rigs inshore and by semi-
submersibles offshore, although some monohull vessels have been built for this
purpose. This has usually been done where there is an also a need to provide oil
storage capacity.

2.5.9 Supply boats
The requirements for these will usually be stated in terms of a clear deck area on
which the extraordinary range of spare parts and stores required by a drilling rig or
a production platform can be stowed. In addition there will generally be a need for
tanks for the carriage of liquid cargoes such as drilling mud. Supply boats are
generally designed so that they can undertake towage tasks and a bollard pull must
therefore be specified.

2.5.10 Safety vessels
In the past, many of these have been converted trawlers but conversions of this sort
have not been able to provide some most desirable requirements which would be
specified for a new build vessel. These should include having a length of ship side
with a low freeboard for the recovery of people from the water and an ability to
manoeuvre quickly and precisely at slow speeds. Although trawlers generally have
good sea-keeping characteristics, this is a subject to which particular attention
would be given on a custom built safety vessel.

2.5.1 I Oil storage and tanker loading facilities

Most of those built so far have been conversions of existing, and generally
redundant, tankers. With fewer of these available in recent years in a condition that
justifies the expenditure of considerable sums on conversion the new building of
this type of vessel is now becoming more attractive.
The most important requirement is the quantity of oil to be stored, together with
the rate at which it will be delivered to the storage vessel by pipeline and the rate at
which it is to be passed on to the shuttle tankers. If, as is usually the case, the
storage vessel is to be moored to a single point mooring buoy that will also carry
the pipeline through which the oil comes on board, details of this interface must be
given. The intended position of the shuttle tanker whether this is to be astern or
alongside must be specified. The sea and wind conditions, respectively, must be
specified for accepting a shuttle tanker, terminating loading and disconnecting the
shuttle tanker, and adopting survival tactics, which may mean abandoning the
pipeline.