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Ship Maneuverability Presentation Transcript
1.SHIP MANEUVERABILITY
2.IT DOES NOT MAKE THE SHIP TURN!
What it DOES do is orient the ship at an angle to the direction of travel…
The pressure on the side of the hull causes the ship to turn (it acts like a flap on an aircraft wing)
What it DOES do is orient the ship at an angle to the direction of travel…
The pressure on the side of the hull causes the ship to turn (it acts like a flap on an aircraft wing)
3.Rudder Nomenclature
4.Rudder Nomenclature
Be familiar with the common types of rudders
Classified by the shape, position, and mounting to the hull
Balanced Rudder The rudder stock is positioned toward the center of the rudder, requiring less force to turn the it
Be familiar with the common types of rudders
Classified by the shape, position, and mounting to the hull
Balanced Rudder The rudder stock is positioned toward the center of the rudder, requiring less force to turn the it
5. Unbalanced Rudder The rudder stock is at the leading edge of the rudder
6. Semi Balanced The rudder mounts on a “horn” protruding from the hull
- The top can be considered “unbalanced”
- The bottom can be considered “balanced”
- The top can be considered “unbalanced”
- The bottom can be considered “balanced”
7.The maneuverability performance of the rudder can be described by three broad categories:
1. Directional Stability
2. Response
3. Slow Speed Maneuverability
8.Directional Stability
- With rudder at midships
- With no external pressure acting on the vessel or rudder
Controls Fixed Straight Line Stability
- A condition rarely achieved
- Any condition other than heading directly into the seas will alter the ability to continue straight
1. Directional Stability
2. Response
3. Slow Speed Maneuverability
8.Directional Stability
- With rudder at midships
- With no external pressure acting on the vessel or rudder
Controls Fixed Straight Line Stability
- A condition rarely achieved
- Any condition other than heading directly into the seas will alter the ability to continue straight
9.- Longer ships are more likely to possess straight line stability
- Short “beamy” ships, like tugs, small sport craft, have poor straight line stability
- To improve this, can increase “deadwood” of the ship
- This is the part of the hull that exists in front of the rudder, an extension of the ship
- Acts like the feathers on an arrow
- Short “beamy” ships, like tugs, small sport craft, have poor straight line stability
- To improve this, can increase “deadwood” of the ship
- This is the part of the hull that exists in front of the rudder, an extension of the ship
- Acts like the feathers on an arrow
10.- When applied, the rudder must be able to change the orientation of the ship in a minimum set time
- The ship must be able to return on course without going beyond the desired heading
- The ability to do so is a function of:
- Ship’s speed (faster = more responsiveness)
- Rudder Area
- Coxswain Ability! (Not in the text, but real life!)
- The ship must be able to return on course without going beyond the desired heading
- The ability to do so is a function of:
- Ship’s speed (faster = more responsiveness)
- Rudder Area
- Coxswain Ability! (Not in the text, but real life!)
11.- Responsiveness is determined by the ship’s mission
- A combatant needs high maneuverability
- A merchant ship needs much less than a combatant
- Can quantify responsiveness by the Rudder Area Ratio:
- A combatant needs high maneuverability
- A merchant ship needs much less than a combatant
- Can quantify responsiveness by the Rudder Area Ratio:
12.- A ship requires some level of maneuverability at low speeds
- In canals
- Approaching harbor entries
- But as speed drops, so too does rudder control!
- Typically require so additional methods to aid turning and positioning in slow speeds
- In canals
- Approaching harbor entries
- But as speed drops, so too does rudder control!
- Typically require so additional methods to aid turning and positioning in slow speeds
13.- Positioning the rudder directly behind the propeller
- Increases water flow over the rudder- Thrust acts directly on the rudder, can be directed by positioning the rudder, creating a turning moment
- Twin Propellers, one acting in reverse, can aid in slow speed maneuvering
- Lateral thrusters (bow thrusters)
- Props oriented athwartship, in a tube at the bow
- Operating thruster creates a force normal to hull, creating a turning moment
- Increases water flow over the rudder- Thrust acts directly on the rudder, can be directed by positioning the rudder, creating a turning moment
- Twin Propellers, one acting in reverse, can aid in slow speed maneuvering
- Lateral thrusters (bow thrusters)
- Props oriented athwartship, in a tube at the bow
- Operating thruster creates a force normal to hull, creating a turning moment
14.Stages of a ships turn:
15.Rudder Stall
- Just like an aircraft wing, if the angle of the rudder is too great, the high and lower pressure areas on the rudder will disrupt water flow over the surface
- Beyond 45o, the rudder will produce no lift, and so will not effectively orient the ship for turning
- Rudder will create turbulence and drag with no effect on ability to turn
- Navy ships typically limit the angle range to about 35o
- Just like an aircraft wing, if the angle of the rudder is too great, the high and lower pressure areas on the rudder will disrupt water flow over the surface
- Beyond 45o, the rudder will produce no lift, and so will not effectively orient the ship for turning
- Rudder will create turbulence and drag with no effect on ability to turn
- Navy ships typically limit the angle range to about 35o
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