WHAT IS SAFEMATIC STEERING ?
Complies with the latest rules and regulations of SOLAS 1974 and all leading classification societies
· Connectable to all HATLAPA ram-type steering gear allowing automatic emergency operation with two independent hydraulic systems
· In case of pipe burst or other defects involving oil leaking, the leakage can be isolated and steering capability is maintained with two cylinders and one pump unit
· Detects, isolates and switches off the defective system automatically within a few seconds
· Steering gear remains operational with the remaining system
· The ship's maneuverability is restored immediately and loss of hydraulic fluid is kept to a minimum, due to the very short time required for automatically detecting, isolating and switching over
· All HATLAPA ram-type steering gears still have their hand operated stop valves for the same purposes.
Safety devices for steering system ?
Hunting gear
Buffer spring
Angle adjusting stop (Hand over position limit switch)
Double shock valve
Relief valve
Tank level alarm (oil)
Over load alarm
Hunting gear, oil flow, and safeties in steering gear?
Hunting Gear is a feed back mechanism of steering gear which re positions the floating lever of hydraulic pump as the tiller moves to the desire position.
Hunting: Due to piston and cylinder wear, there will be slippage of oil through. Rudder can not be kept in helm as the pump can not provide effective hydraulic locking. So, rudder can be easily displaced from the required position by the action of waves etc. Hunting gear will take action to return the rudder in ordered position.
Purpose of Hunting Gear:
1. Hunting gear floating lever mechanism is required to bring the rudder to the ordered position.
2. Also this mechanism is required to position the rudder in its ordered position when the action of water,
waves or propeller force displaces the rudder from its ordered position.
the hunting gear brings the rudder to its ordered position against the water, wave etc.
3. It is feed back mechanism of steering gear which re positions the floating lever of hydraulic
pump as the tiller moves to the desire position.
Why spring links are incorporated in the hunting gear?
1. The spring called buffer spring is incorporated in the hunting gear links to take up any excess movement beyond the maximum stroke of the pump. This extra movement is stored by the compressed spring and reset when hunting gear approaches the no-effect point to prevent the mechanical damage of the pump.
2. Also buffer spring will take up the shock movement of rudder due to heavy sea, thus preventing excessive hunting action of pump.
Safety devices for steering system ?
1. Hunting gear
2. Buffer spring
3. Angle adjusting stop (Hand over position limit switch)
4. Double shock valve
5. Relief valve
6. Tank level alarm (oil)
7. Over load alarm
STEERING GEAR TEST BEFORE DEPARTURE.
Control test - Just prior to 1 hour before departure of vessel.
12 hour before departure.
Operation of main & auxiliary steering gear.
Operation of remote control system.
Operation of emergency power supply.
Alarm test.
Actual rudder angle & indicator.
Communication system.(Bridge, Engine room & Steering gear room)
Every 3 months interval.
Emergency steering gear drill at steering gear room to bridge with sound communication system
Test required before departure ?
Steering gear should be checked at least one hour prior to departure.
Telemotor transmitter oil level to be checked
Oil level of actuating system tank should be checked and replenished if necessary.
Rudder carrier bearing and bottom sea gland checked and greased.
Start pump and check response of the gear
Check abnormal noise and heat
Check load carrying and running of the gear
( swing from port 35 to STBD 30 within 28 sec )
Difference b/w steering motor and other motor on board?
The steering gear motor does not have overload trip but only have alarm.
Only trip provided on steering motor is short circuit fuses.
Explain rudders and its types.
A rudder allows the ship to turn, simple plates have been superseded by plates welded to cast or fabricated frame. Rudders are hollow and so provide for some buoyancy . In order to minimize the risk of corrosion internal surfaces are provided with a protective coating and some are even filled with foam.
A drain plug is provided to allow for the drainage of water , enable internal inspection to be made using fiber optic device and even allow for the limited application of a protective coating. Plates are welded to the frames internally in order to provide flush fitting , the final closing plate must be welded externally.
A means of lifting is provided taking the form of a tube as close to the center of gravity as possible. Rudders are tested to a pressure head 2.4m above the top of the rudder.
If the rudder has its entire area aft of the rudder stock then it is unbalanced .A rudder with between 20 and 40% of its area forward of the stock is balanced since there will be some angle at which the resultant moment on the stock due to the water force will be zero. Most modern rudders are of the semi-balanced design.
This means that that a certain proportion of the water force acting on the after part of the rudder is counter acted by the force acting on the for'd half of the rudder; hence, the steering gear can be lighter and smaller. A rudder may lift due to the buoyancy effect, the amount of lift is limited by the jumper bar fitted to the stern frame. The jumper/rudder clearance must be less than the steering gear cross head clearance to prevent damage.
A rudder is supported by means of a bearing pintle or a lower bearing depending upon the design. Where a lower bearing is employed the rudder is actually supported on split bearing rings fitted on the lower face of the rudder and the upper face of the sole piece ( the extended lower section of the stern frame upon which the rudder sits)
Fully balanced rudder
- a cylindrical static casing (stator) with usually three internal vanes which project radially inwards
- a rotor keyed to and concentric with the rudder stock, the rotor has rotor vanes which project radially outwards into the spaces formed by the stator vanes.
To reduce the amount of torque required to turn a rudder the pivot point is moved back from the leading edge. The amount of torque then varies depending on the angle of attack. Zero torque leads to instability with rudder moving within its clearances.
Spade rudder
The reduced diameter at the upper part is purely to transmit torque. The lower section must also support bending moments and hence increased diameter. With twin rudder ships the inner rudder must turn through a greater angle than the outer. This is achieved by having the tiller arm at an angle to the centre line of the rudder.
It is possible to have the blades angled in or out when the wheel is amid ships to increase propulsive efficiency.
How the 4 Ram type steering gear works?
When the wheel 1 (usually called a steering wheel) is turned anticlockwise, the pinion 2 moves the toothed rack 3 downward and moves the toothed rack 4 upward. As it is fixed to the two piston 5 and 6, the piston also moves correspondingly. As these two cylinders 7 & 8 are filled with oil, the movement of the pistons result in oil pressure being applied to the bottom of the piston 10 and moves it upward and these forces the oil in upper part of cylinder 9 up in to the cylinder 8.
Piston 10 has a piston rod connected to a slide valve 11. In its middle position, the slide valve just closes the ports 12, 13, 14 in the slide valve housing 15. As the piston 10 moves upward, the slide valve 11 also moves along with it and opens port 12 and 14. These cause oil from the pressure vessel to come under side of the piston 20 and the oil above piston 20 is forced in to the slide valve housing 15 and out through the port 12 to the discharge tank 16. As a result the piston 21 moves upward along with the piston 20 since both these piston are connected together by piston rod. These upward movements of the two pistons impart movement to the tiller arm which is mounted on the rudder stock and hence moves the rudder.
How the rotary vane type steering gear works?
These consist of two elements:
The spaces formed between the stator and rotor vanes are used as high and low pressure chambers. The main advantage of the system is that it is compact, occupying about 1 / 10 the space of a ram system The chambers are alternately connected to the suction and delivery from the hydraulic pump so that they can be used to produce the rudder actuating torque. Because the distribution of the pressure chambers is balanced around the rudder stock, only pure torque is transmitted to the stock and no side loading are imposed by the gear.
There are two main types of rotary vane steering gear in use today. One has its stator firmly fixed to the steering flat deck and the stator housing and cover are provided with suitable bearings to enable the unit to act as a combined rudder carrier and rudder stock bearing support. The other type of vane gear is supported where the stator is only anchored to the ships structure to resist torque but is free to move vertically within the constraints of the separate rudder head bearing and carrier which is similar to the bearing provided for ram type steering gears.
What are the follow up and non follow up in steering gear systems?
Non follow up system
When steering gear set to required position, rudder is moved & when rudder reach the required position, steering gear must be set to off position. This system uses the three solenoid valve.
Follow up system
When steering gear set to required position, rudder is moved & when rudder reaches the set position, steering gear still remains at that position. This system uses the hunting gear arrangement.
. Properties of telemotor hydraulic fluid ?
Low pour point (-50°C)
Low viscosity ( to reduced fractional drag, but not too thin to mate gland sealing,
30 Redwood Secs at 60°C)
High viscosity index (110)
High flash point (150°C closed)
Non sludge forming
Non corrosive
Good lubricating properties
Specific gravity 0.88 at 15.5°C
M Purpose of buffer spring
Absorb the difference between the steering order speeds and follow up speed.
Absorbed the movement of steering wheel if it is mishandled when the hydraulic pump stop in.
Absorb the movement of the control lever when rudder drift
Absorb the vibration and shocks from the rudder.
Daily check in steering gear room
Pressure gauge of steering pump.
Motor ampere on the steering switch board & motor hand touch feeling
Noise and vibration.
Oil level in tank
Oil leakage in system
Grease in rudder carrier bearing
Check the bottom seal gland whether good or not.
Steering system regulation.
Every ship shall be provided with a main steering gear and an auxiliary steering gear. The failure of one of them will not render the other one inoperative.
Relief valves shall be fitted to any part of the hydraulic system. The main steering gear and rudder stock shall be:
A of adequate strength and capable of steering the ship at maximum ahead service speed.
A capable of putting the rudder over from 35' on one ides to 35' on theother side with the ship at itsdeepest sea going draught and running ahead at maximum ahead service speed and, under the same conditions, from 35' on either side ot 30' on the other side in not more than 28 seconds.
A So that they will not be damaged at maximum astern speed.The auxiliary steering gear shall be:
A of adequate strength and capable of steering the ship at navigable speed and of being broughtspeedily into action in an emergency.
A capable of putting the redder over from 15' on one side to 15' on theother side in not more than 60seconds with the ship at its deepest seagoing draught and running ahead at one half of the maximum ahead service speed or 7 knots, whichever is the greater.
In every tanker, chemical tanker or gas carrier of 10,000 gross ton and upwards and in every ships of 70,000 gross ton and upwards, the main steering gear shall comprise two or more identical power units.
Essential requirement for steering gear.
a To move the rudder in either direction instantly, when required.
a Should come to rest immediately in the position corresponding to that shown on indicator.
a Provisions must be made to protect the steering gear from damage should a heavy sea strike the rudder.
a The design should be simple, the construction robust and its performance reliable at all times.
Tests required before departure.
a Steering gear should be checked at least one hour prior to departure.
a Telemotor transmitter oil level to be checked.
a Oil level of the actuating system tank should be checked and replenished if necessary.
a Rudder carrier bearing and bottom sea gland checked and greased.
a Start pumps and check response of the gear. a Check load carrying and running of the gear.
