Steering Gear Safematic

Steering GearSteering Gear

THE SINGLE THE SINGLE FAILURE CRITERIA FAILURE CRITERIA (Safematic design of (Safematic design of steering system)steering system)

Some oil tankers, gas Some oil tankers, gas tankers & chemical tankers & chemical tankers are required tankers are required to have a safematic to have a safematic design of steering design of steering system i.e. no single system i.e. no single failure on a steering failure on a steering should make the should make the steering of the ship steering of the ship inoperative and thus inoperative and thus give the rudder a give the rudder a chance to become chance to become free.free.


If, in the 4 Rams hydraulic system If, in the 4 Rams hydraulic system described the leakage had developed at described the leakage had developed at say point "X" (say point "X" (as happened in case of `MT as happened in case of `MT Ameco Cardiz' that resulted in total loss of Ameco Cardiz' that resulted in total loss of the tanker and its cargothe tanker and its cargo), there would be ), there would be no way to isolate this leak to have the no way to isolate this leak to have the steering capability of the system available steering capability of the system available to the ship after the leak. to the ship after the leak.

To take care of such leaks (i.e. leaks To take care of such leaks (i.e. leaks outside isolating valves of the rams), outside isolating valves of the rams), safematic designs have been developed.safematic designs have been developed.


Safematic Design: Safematic Design: Method No.1 Method No.1 (Also (Also called 100% redundancy called 100% redundancy method), refer figure method), refer figure

All valves are All valves are automatically controlled automatically controlled and electrically operated and electrically operated valves.valves.

In this arrangement In this arrangement System I supplies to ram System I supplies to ram No. I & 2 . System 2 No. I & 2 . System 2 supplies to ram No. 3 & supplies to ram No. 3 & 4 . However, as it is not 4 . However, as it is not practical to have both practical to have both systems work systems work simultaneously, and simultaneously, and therefore the only therefore the only combination of combination of operations available are:operations available are:


Combination No. 1:Combination No. 1: Isolating valve I & 2 Isolating valve I & 2 open, By pass valve 5 open, By pass valve 5 shut; system No. I shut; system No. I In In operation. operation.

Isolating valve 3 & 4 Isolating valve 3 & 4 shut, By pass valve 6 shut, By pass valve 6 open; system No. 2 open; system No. 2 stopped stopped

Top two rams are in Top two rams are in operation, working on operation, working on system No. I and are system No. I and are providing 100% providing 100% torque. torque.

Bottom two rams & Bottom two rams & system No. 2 is shut.system No. 2 is shut.


Combination No.2:Combination No.2: Isolating valve 3 & 4 Isolating valve 3 & 4 open, By pass valve 6 open, By pass valve 6 shut, system No. 2 shut, system No. 2 in in operation. operation.

Isolating valve 1 & 2 shut, Isolating valve 1 & 2 shut, By pass valve 5 open, By pass valve 5 open, system No. stopped system No. stopped

Bottom two rams are in Bottom two rams are in operation, working on operation, working on system No. 2 and are system No. 2 and are providing 100% torque. providing 100% torque.

Top two rams & system Top two rams & system No. l is shut.No. l is shut.


Now the logic circuit of safematic design in Now the logic circuit of safematic design in this method will cause the condition this method will cause the condition of of operation to change from Combination No. I operation to change from Combination No. I to Combination No.2 or Combination No.2 to Combination No.2 or Combination No.2 to to Combination No. 1 (depending on which Combination No. 1 (depending on which Combination was in operation when the Combination was in operation when the heavy loss of oil LLL (Low low level) alarm is heavy loss of oil LLL (Low low level) alarm is actuated).actuated).


Example if Combination Example if Combination No.1No.1 is in is in operation, (i.e. system No.1 & rams No. operation, (i.e. system No.1 & rams No. 1& No. 2 are in operation) & LL (Low level) 1& No. 2 are in operation) & LL (Low level) alarm actuates. This alarm takes care of alarm actuates. This alarm takes care of normal leakage & can be set right by filling normal leakage & can be set right by filling in some oil in the tank during the watch.in some oil in the tank during the watch.


However, if LLL (Low low level) alarm follows However, if LLL (Low low level) alarm follows immediately, it indicates a heavy loss of oil and logic immediately, it indicates a heavy loss of oil and logic circuit will cause the condition of operation change circuit will cause the condition of operation change from Combination from Combination No.1No.1 to Combination to Combination No.2.No.2.

It may be noted that as said earlier even though we It may be noted that as said earlier even though we have 4 rams, only 2 rams are in operations at any have 4 rams, only 2 rams are in operations at any given time. Thus each set of 2 rams should provide given time. Thus each set of 2 rams should provide 100% torque.100% torque.

Most ships will not employ this method to take care of Most ships will not employ this method to take care of “single failure criteria, as this method means a 100% “single failure criteria, as this method means a 100% duplication and a costly one. duplication and a costly one.


Combination No. 1:Combination No. 1: Isolating valve I,2,3 & 4 Isolating valve I,2,3 & 4 open, By pass valve 5 & 6 shut; system No. I open, By pass valve 5 & 6 shut; system No. I oror system No. 2 working. All 4 rams are in system No. 2 working. All 4 rams are in use and provide together 100% torque. use and provide together 100% torque.

Combination No.2: Combination No.2: Valve ‘a’ & ‘b’ shut. Valve ‘a’ & ‘b’ shut. Isolating valve I & 2 open, By pass valve 5 Isolating valve I & 2 open, By pass valve 5 shut; system No. I working. Isolating valve 3 & shut; system No. I working. Isolating valve 3 & 4 shut, By pass valve 6 open; system No. 2 4 shut, By pass valve 6 open; system No. 2 shut. Top two rams are in operation, working shut. Top two rams are in operation, working on system No. I and are providing 50% torque. on system No. I and are providing 50% torque. Bottom two rams & system No. 2 are Bottom two rams & system No. 2 are isolated.isolated.


Combination No.3: Combination No.3: Valve ‘a’ & ‘b’ shut. Valve ‘a’ & ‘b’ shut. Isolating valve 3 & 4 open, By pass valve 6 Isolating valve 3 & 4 open, By pass valve 6

shut, system No. 2 working. shut, system No. 2 working. Isolating valve 1 & 2 shut, By pass valve 5 Isolating valve 1 & 2 shut, By pass valve 5

open, system No. stopped.open, system No. stopped. Bottom two rams are in operation, working on Bottom two rams are in operation, working on

system No. 2 and are providing 50% torque. system No. 2 and are providing 50% torque. Top two rams & system No. l are isolated.Top two rams & system No. l are isolated.


Logic circuit of this safematic design shall on Logic circuit of this safematic design shall on detecting a heavy leak actuate low low level detecting a heavy leak actuate low low level (LLL-1) alarm and cause change over from (LLL-1) alarm and cause change over from condition No.1 to condition No.2 or condition condition No.1 to condition No.2 or condition No.3. No.3. And if the leak persists in the system, it will And if the leak persists in the system, it will actuate (LLL-2) alarm. This will cause change actuate (LLL-2) alarm. This will cause change of the condition further from condition No.2 to of the condition further from condition No.2 to condition No.3 or condition No.3 to condition condition No.3 or condition No.3 to condition No.2 (depending on what was the existing No.2 (depending on what was the existing condition.)condition.)


Steering Gear Safematic

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