278 Bulletin, Scripps Institution of Oceanography 
3) Corrosion and decay.—The conductivity of sea water makes it essential that 
no dissimilar metals be in direct electrical contact. The potential difference even 
between hot-dipped and electrolytically galvanized parts is sufficient to cause 
failure if they are submerged and in contact for several months. 
The oxygen concentration in some places in the open ocean is as low as 0.15 ml/1 
at mid-depths. Many metals, including some stainless steels, are inadequately pro- 
tected at such low tensions. 
It is well known that bacteria, fungi, and boring animals in the sea are very 
destructive to most organic materials. Hither resistant or toxie coatings must be 
used, or components must be built of materials not subject to attack. 
4) Other factors—Sharks are voracious creatures of the deep sea which will 
strike or bite at any object that attracts their attention. A small float on a line, a 
tag end of line, or tape on an instrument eable is frequently bitten off or damaged 
by sharks. It is essential that every component appear continuous with the system 
in order to minimize shark bites. That is, tags, pigtails, and small floats of colors 
different from that of the line should be avoided. 
Seaweed rafts appear close in to coasts, often at oceanic fronts. A surface pen- 
nant will become fouled by such rafts, and if the raft is large enough it will carry 
the mooring away. Nipa and rattan rafts of immense dimensions are present in 
some parts of the South Pacific. Where this problem is likely to be severe, and 
the mooring must survive for long periods of time, the mooring may of necessity 
have to be designed with no surface float. 
Where sea ice is present, it is not possible to employ moorings with surface 
floats. In sleet or black-ice storms at high altitudes, ice may build up on the float. 
If these factors are hazards, the float should be designed to survive capsizal. 
Near rocky coasts, seals and sea lions sometimes are troublesome in that they 
leap aboard and bask on any surface float large enough. They may break antennae 
or even capsize the float. They may be discouraged by designing the float without 
flat horizontal surfaces or by using a rough granular coating. 
On the bottom in the deep ocean, there are a number of sharp objects: debris 
that has been jettisoned, wrecks, rock outcroppings and nodules, as well as, of 
course, the anchor. In general, therefore, any part of the mooring cable which is 
allowed to touch and drag on the bottom must be chain or flexible wire rope of 
high quality, several times stronger than the main mooring cable. 
Perhaps the most difficult problem stems from human intervention. If the sur- 
face floats on a mooring are conspicuous, visually or by radar, passing craft will 
pull off course to investigate. If there are any floating lines about the float they 
are very likely to be picked up on the hull or in the screws and cut adrift or keel- 
hauled. In addition, fishermen will tie up to the moorings, attempt to hoist them, 
or cut them free. In many instances this recovery is intended to be helpful. Regard- 
less of warnings or information painted on the float, some seamen cannot believe 
that a floating object in 2,000 or 3,000 fathoms is moored there, and will salvage 
it and return it to its owner. 
The importance of these environmental factors may perhaps be indicated by 
the fact that, of fifteen moorings broken loose and recovered by Scripps Institu- 
tion, only two or three seemed to have failed from mechanical stress, fatigue, or 
