prevent brute force techniques from being em- 
ployed in deeper waters. 
In recent years, dynamic systems have been 
developed to position surface platforms in deep 
water. Water depth, positioning accuracy require- 
ments, operational conditions, and platform size 
economically justify a dynamic positioning system 
for some applications. For most deep water 
floating platforms, however, direct attachment to 
the bottom is necessary. 
New materials are replacing the traditional steel 
cables and chains. Nylon, dacron, and polypro- 
pylene reduce weight and minimize corrosion 
problems of deep moors. New developments in 
fiber glass cables and chains also promise corro- 
sion-free, high-strength moorings. Connecting de- 
vices of commensurate performance are required. 
The stable surface platform, or specialized 
buoy, must perform a variety of tasks peculiar to 
the ocean environment. Special equipment is 
required to meet these needs. Surface platforms 
and buoys have particular requirements for posi- 
tion accuracy which vary widely. The required 
position accuracy usually is stated with respect to 
geographic location. Horizontal accuracy is de- 
fined as its watch circle (the area to which the 
platform’s horizontal movement is restrained). 
A system for maintaining buoy or surface 
platform position with respect to geographic loca- 
tion or bottom reference for extended periods is a 
primary requirement, except for intentionally-free 
buoys. Fixed moors require techniques to predict 
and counteract forces in the mooring cables. If 
embedment in rock is necessary, explosive anchors 
or equivalent techniques must be used. 
Dynamic positioning systems incorporating var- 
ious thrust control techniques (cycloidal propel- 
lers, directable propulsion units, or bow and stern 
thrusters) must undergo further evaluation at sea. 
Automatic control systems must be developed to 
signal corrective action depending upon inputs, 
surface conditions, and navigational data; an ex- 
perimental system should be built and tested at 
sea. Finally, options between fixed mooring and 
dynamic positioning must be studied. 
The horizontal watch circle in which a moored 
platform may move is influenced by design provi- 
sions. As the watch circle is decreased, greater 
demands are imposed on the anchor, which must 
resist both the horizontal drag of the buoy or 
platform and the vertical pull of the taut mooring 
line. 
Vertical stability can be achieved through ap- 
propriate hull shapes like that of FLIP (Figure 12). 
The platform’s design characteristics result in a 
hull with minimum response to the forces imposed 
by passing waves. 
Figure 12. Floating Instrument Platform 
(FLIP). Draft is 300 feet in vertical position. 
(Navy photo) 
b. Future Needs Technology leading to more 
stable and durable buoys and platforms is inter- 
related with many disciplines. It begins with a 
better understanding and definition of the winds, 
sea state, and currents over long periods and their 
dynamic interaction with floating vessels and 
platforms. The following specific improvements 
are needed: 
—Methods to survey bottom conditions and pre- 
dict anchoring characteristics of bottom sedi- 
ments. 
—New types of anchors with greater holding power 
in different bottoms at greater depths. 
