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Oakum. A substance made from soft vegetable fiber such as hemp and jute impregnated with pine tar. It is principally used for caulking the planking on wood decks of steel vessels and for caulking all the planking on wood ships where watertightness is desired, It is also used for caulking around pipes.

Oakum Spinners. Men who take the bulk oakum from the bales and roll or spin it into a loose or soft rope, called a thread, of the proper size to allow it to be driven into the seams between the planks.

Octant. An instrument for measuring angles, with a graduated arc of 45°.

Offing. That distance out from shore which permits the proper maneuvering of a vessel without danger of her taking the ground or of encountering other obstacles to her freedom of movement.

Offset. A term used by draftsmen and loftsmen for ordinate to ship’s curves. See Joggle, for its meaning in structural work.

Ohm. A practical unit of electrical resistance. lt represents the resistance of a column of pure mercury 106.3 cm. long, of uniform cross section and weighing 14,4521 gm. at O° C.

Ohm’s Law. The current in a direct current circuit is proportional to the e. m. f. and inversely proportional to the electrical resistance (i.e., the current is equal to the voltage divided by the resistance).

Oil Burner. A device for vaporizing or atomizing oil so that it burns like a gas.

Oil Cooler, Lubricating. A device on the order of a condenser, except that the cylinder is installed with its axis vertical. Numerous brass tubes, through which cold water circulates, pass between the top and bottom tube sheets and the oil is cooled by coming in contact with their cold surfaces. Baffles are generally installed compelling the oil to pass back and forth among the cold tubes in traveling from the top to the bottom.

Oil, Creosote. An oil obtained by the redistillation of crude tar which, in turn, is derived as a distillate in the destructive distillation of wood.

Oil Forge. A forge in which oil is used as fuel.

Oil, Fuel. A heavy mineral oil used extensively in place of coal for firing boilers.

Oil Furnace. See Furnace, Oil.

Oil, Hard Wood. Oil obtained from the tar of a hardwood by redistillation.

Oil, Pine. An oil, lighter than water, obtained by distillation from the crude resins and turpentine gathered from the pine tree.

Oil Piping. See Piping, Oil.

Oil, Pump. See Pump, Oil.

Oil, Resin. An oil obtained from resin by redistillation at high temperatures.

Oil Service Tank. In a lubricating oil system the tank from which the oil feed pipes lead in supplying the various journals, etc. In a fuel oil system the tank or tanks from which oil is drawn direct to the burners.

Oil Tight Bulkhead. See Bulkhead, Oil Tight.

Oil tight. Having the property of resisting the passage of oil. In shipwork this is accomplished by packing or calking after careful riveting of the joints.

Oilers. Members of a ship’s engine room force who attend to the lubrication of all parts of the engines.

Old Man. A piece of heavy bar iron bent to the form of a "Z." One leg of the "Z" is bolted to the material that is to be drilled, and the drill top placed under the other leg and adjusted so the "old man" holds the drill against the material.

On Board. Aboard; in or on a ship, but having a different significance from "on deck" in that "on board" applies to any location in or on the ship as any of its parts, while the term "on deck" is generally limited to a location on the weather deck.

On Deck. On the weather deck; frequently used to imply "on duty."

Open Bridge House. A bridge house open to the weather at each end.

Open Hearth Steel. See Steel and Iron.

Operating Gear, Turbine. See Turbine Operating Gear.

Ore Carrier. A vessel designed to carry ore in bulk and similar in construction to a collier.

Orlop Beam Stringer. See Stringer, Orlop Beam.

Orlop Deck. See Deck, Orlop.

Orlop Deck Stringer. See Stringer, Orlop Deck.

Orlop Deck Stringer Bar. See Stringer, Bar.

Orlop Stringer. See Stringer, Orlop.

Orrery. A clockwork model of the planetary system, named after Charles Boyle, fourth Earl of Orrery.

Oscillating Engine. See Engine, Oscillating.

Oscillation. The roll of a ship from the extreme angular position on one end to the corresponding position on the opposite side.

Oscillation, Arc of. The total angle swept through by a ship in one oscillation.

Oscillation, Period of. The time occupied by a ship in performing one complete oscillation.

Outboard. Away from the center toward the outside; without the hull.

Outboard Delivery Pipe. See Pipe, Outboard Delivery.

Outboard Profile. A plan representing the longitudinal exterior of a vessel showing the starboard side of the shell, all deck erections, masts, yards, rigging, rails, etc.

Outer Bearing. A term applied to the bearing on the sponson supporting the outer end of the paddle wheel-shaft.

Outer Keel. See Keel, Outer.

Outer Skin. See Skin, Outer.

Outlet Cock. A cock or valve with a circular channel through the valve stem arranged so that a clear opening is obtained by 90 degrees rotation, located so as to drain any receptacle.

Outermost Fiber. In calculating the strength of vessels, that part of the vessel’s strength girder which is farthest away from the neutral axis of the strength section.

Outrigger. A term applied to a small racing boat having the oarlocks located on framework extending beyond the sides.

Outriggers. A term applied to bars bolted to the outer ends of the cross-trees on each side of a mast for the purpose of spreading the stays to the topmasts. Also applied to the upper mast tables which form a support for the topping lifts operating the cargo booms.

Outside Plating. See Shell Plating.

Outside Strake. See Strake, Outside.

Oven, Bake. A commissary appliance used on board ship for baking bread, pastries, etc. The oven proper consists of one or more chambers externally heated, electrically or by burning coal or fuel oil.

Oven, Core. An oven in which cores used in foundry work are baked to insure their holding their form while pouring the molten metal.

Oven, Drying. An enclosure or room in which green timber is seasoned by the application of dry heat for a given period of time.

Overflow Pipe. A pipe fitted on a tank or compartment to permit excess liquid to escape, thus preventing undue pressure on the tank.

Overhang. That portion of a vessel’s bow or stern which projects beyond a perpendicular at the waterline.

Overhaul. To repair or to put in proper condition as to overhaul a tackle. Where two vessels are going in the same direction and where one vessel is ahead of the other, the vessel behind is said to be overhauling the vessel in the lead when it is closing up the distance between the two by going at a faster speed.

Oxter Plate. See Plate, Oxter.

Oxygen Compressor. See Compressor, Oxygen.

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