The thermometer provided within the intake pipe when the ship is built is normally not suitable
for the measurement of sea surface temperature. Thus the Member recruiting the ship should,
with the permission of the shipping company concerned, install a thermometer appropriate for
the purpose. This should preferably be mounted in a special tube providing adequate heat
conductivity between the thermometer bulb and the intake water.
When a direct-reading thermometer is installed in cramped conditions the observer should be
warned of the possibility of error in his readings due to parallax. A distant-reading system with
the display elsewhere (e.g. in the engine room or on the bridge) overcomes this problem. The
observer should also be aware that for ships of deep draught, or when a marked temperature
gradient exists within the sea surface layer, intake temperature readings usually differ
considerably from those close to the sea surface. Finally, of course, the intake temperature
should not be taken when the ship is stationary, for then the cooling water is not circulating.