Main         Home  |  CO's Welcome  |  Sea Cadet Corps  |  Our Unit  |  Junior Section  |  Things we get up to
Menu :     Ship's Company  |  Parents  |  Adult recruitment  |  Find Us  |  FAQ  |  British Navies  |  Site map

This description is made up of three sections:

Some of the information below, such as helm orders and technichal bits, is not on the Sea Cadet Corps syllabus, but is included for those who are interested.

1.   SHIP TERMINOLOGY

Parts of a Ship

Bow – Stem – Forecastle - Hawse pipe – Weather decks - Draft - Freeboard - Superstructure - Bridge - Mast - Yardarm - funnel - Keel - Shaft - Propeller - Rudder - Stern - Waterline

Other terms

2.   FORCES ON SHIPS

PROPULSION PLANT

Power train: power source (ENGINE) turns a shaft (through reduction gears), which turns a propeller. (Click on diagram of Hydra Class frigate below for larger image.)

.PROPELLERS may be fixed propellors or controllable pitch propellors (CPPs):

• Fixed: Ship speed is controlled by shaft rpm only
• CPP: Ship speed is controlled by both shaft rpm and propeller blade pitch

In addition to fore and aft thrust, propeller rotation also causes what is known as “side force”: Side force is a lateral force caused by propeller rotation. The direction of the force is the direction in which the propeller would “walk” along the bottom due to its rotation §.

ENGINES

Almost all Navy ships have one of three ENGiNE TYPES:

• Gas turbine: (requires CPP): most surface combatants
• Diesel: Large auxiliaries, minesweepers
• Steam: (Conventional or Nuclear): Older ships, aircraft carriers, submarines

AUXILIARY PROPULSION UNIT (APU)

Also known as a Bow Thruster, an Auxiliary Propulsion Unit (APU) is a hull-mounted, transverse propeller used to develop lateral thrust when pierside. It is normally found on larger ships. It is retractable, omni-directional and can be used for emergency propulsion on single-screw ships and for pierside manoeuvring §.

RUDDERS

Configuration: normally one rudder for each propeller, mounted directly astern of the propeller.
Range of motion: 35° left or right of CL

Rudder effectiveness is dependent on flow velocity over the rudder surface. Bare steerageway is the minimum speed at which a rudder is still effective. This is generally 2 to 3 knots for most ships. Rudder angles must be reversed for astern operation §.

MOORING LINES

Lines are used next to a pier to control ship positioning.

Each line has a specific name, indicating location, direction, and purpose. Lines are numbered, fore to aft, based on location on the ship:

TUGS

Tugs are used to assist ships in pierside manoeuvres. Three ship-to-tug tie-ups are used:

• Single headline: Simple; effective for steady pushing/pulling in one direction
• Double headline: Allows tug to push the ship both ahead and astern
• Power: Best general purpose tie-up; allows tug to use engines and rudder in any direction without moving itself §.
  

SHALLOW WATER EFFECTS

Increased resistance: In relatively shallow water at high speeds, pressure drag on the hull is significantly increased, resulting in actual speed less than ordered speed.

Squatting: The ship’s bow wave is increased, resulting in a lifting of the bow and sinking of the stern §.

3. STANDARD COMMANDS

The trend in merchant ship navigation is for fewer crew members on duty and more automation, away from the style of operation associated with navies and towards the 'one man bridge' scenario, where the vessel's automatic systems are controllable by the `conning officer'. In the latter case, there is less need for the type of command sequences described below.

COMMANDS TO THE HELM

Format Example

Direction, {Amount}, {Course}

Amount: Expressed as a number of degrees of rudder (10°, 15°, etc.), or one of the following: (nominal values given)

For small course changes of 10° or less, a specific rudder angle is not given. This allows the Helm to use up to 10° of rudder to make the course change.

Course to steer: Expressed as a number of degrees. If not given, the Helm maintains the rudder at the ordered angle until another order is given.

HELM REPLY

Whenever an order to the Helm is given, the Helm repeats the order back to the Conning Officer word-for-word. This assures the Conning Officer that the order was heard and understood correctly. e.g.

The Conn orders: “Right standard rudder, steady course 260.”
The Helm replies: “Right standard rudder, steady course 260, aye.”

If the helm does not understand an order from the Conn, the helm will reply: “Orders to the helm”.
The Conn should immediately check his/her order and restate it clearly to the Helm.

REPORT

Once a desired action is complete, the Helm reports it to the Conn §.

ACKNOWLEDGEMENT

The Conn acknowledges all reports with “Very well’
If the Conn does not acknowledge a report, the Helm should repeat the report until acknowledged.

EXAMPLES OF COMMAND SEQUENCE
Order: “Right standard rudder, steady course 298.”
Reply: “Right standard rudder, steady course 298, aye.”
Report: “Sir, my rudder is right standard, coming to new course 298.”
Acknowledgment: “Very well.” §

ENGINE ORDERS

For fixed pitch propellers, ship speed is dependent on shaft rpm only.
For controllable pitch propellers, ship speed is dependent on shaft rpm and, below about 12 knots, propeller blade pitch.
For gas turbines, the shaft is always spinning when the engine is on line. “All engines stop” is achieved by a blade pitch of 0°.

Prescribed standard speeds are predetermined ship’s speeds:

Engines: Port, Starboard, or All Engines. (Unnecessary for single screw ships.) e.g. ”All engines . . ."
Direction: Ahead, Back or Stop, followed by the nearest standard speed (except for stop) e.g. ". . ahead full. . ." ". . .back 2/3. . ."
Speed: specify pitch (for controllable pitch propellors), turns and knots e.g. ". . .indicate 072 revolutions and 20% pitch for 3 knots." §

REPLIES, REPORTS AND ACKNOWLEDGEMENTS TO ENGINE COMMANDS
Reply: Word-for-word repeat-back is required.
Reports: Lee Helm reports when action is completed, including the complete status of all engines.
Acknowledgement: Conn will acknowledge all reports with “Very well”

EXAMPLES
Order: “All engines ahead standard indicate 115 revolutions for 16 knots.”
Reply: “All engines ahead standard indicate 115 revolutions for 16 knots, aye.”
Report: “Ma’am, engine room answers all engines ahead standard, indicating 115 revolutions for 16 knots.”

MAN OVERBOARD

Immediate actions - sound 6 or more short blasts; designate bridge team member to drop a smoke in the water - but not for aircraft crash (fuel in water)
Additional actions - notify captain & other ships; hoist Oscar flag (day) or turn on red-over-red pulsating (night)
Recovery - helicopter average time to ready for takeoff is 10-12 mins; small boat average time to launch 6-8 mins; ship is the fastest method
Manoeuvring - Anderson, Race Track, Williamson, Tear Dro and Y-backing are all Man Overboard manoeuvres, each appropriate in a particular situation §.

SIMPLY THE BEST - THAT'S THE SEA CADETS !