DICTIONARY OF

Oceanus 240 Okta
Oceanus. In ancient mythology was the god of the river Oceanus. He and his wife, Tethys,
were parents of all rivers, and of 3000 nymphs (Oceanides).
Octant. Reflecting instrument with arc of 45°, and graduated to 90°.
Oertz Rudder. Streamlined rudder designed to reduce eddy currents from propeller streams
and to eliminate dead water.
Off and Fair. Order to take off a damaged member of a vessel, to restore it to its proper
shape and condition, and to replace it in position.
Off and On. Said of a sailing along a coast when progress is made by alternately standing in
towards the land and standing off it.
Officer of the Watch. Officer in charge of a watch for the time being.
Official Log. Book in form approved by Dept. of T. & I. issued to Master of a British ship
when engaging crew. Is entered with information required by Merchant Shipping Acts
concerning such matters as draught of water on sailing, any casualty affecting the vessel,
marriages, births, or deaths occurring on board, disciplinary action taken against offenders,
particulars regarding boat and other drills, deck cargo carried, etc. At end of voyage is
delivered to Superintendent of Marine Mercantile Office.
Offing. Sea area lying between visible horizon and a line midway between horizon and
observer on the shore. To keep an offing is to keep a safe distance away from the coast.
Off the Wind. Sailing with wind abaft the beam. Sometimes used to mean being further from
wind than justifiable while sailing close-hauled. Said of cowl ventilator when back to wind.
Ohm. Unit of electrical resistance. Equivalent to force of one ampere of current at a pressure
of one volt. Standardised as resistance set up in a column of mercury, of uniform diameter,
with temperature of 0°C, mass of 14.4521 grammes, length of 106.3 centimetres.
Ohm's Law. Links up relationship between electrical current, voltage, and resistance by
formula E = CR when E is voltage, C is current in amperes, and R is resistance in ohms.
Oil Bag. Canvas bag containing oakum, or waste, saturated with oil. Veered, when required,
for modifying storm waves.
Oil Fuel. Petroleum residue used in furnaces for raising steam in boilers. Flashpoint must be
at least 150°F for marine purposes. Heat value is about 1.3 that of same weight of coal - but
about 1.6 bulk for bulk.
Oiling. Taking in oil fuel. Lubricating machinery.
Oilskins. Waterproof clothing made of calico and soaked with linseed oil, or covered with a
bitumastic preparation.
Oil Tanker. Vessel specially constructed and fitted for carrying oil in bulk.
Okta. Unit equalling in area to 1/8 of sky, used in specifying cloud amount.