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The Sea Stabilization debate around Marine Radars

The problem of human mind is its tendency to become fixated with any IDEA that it receives with overwhelming emotions.

Even as the young seafarers started to understand the importance of the STW (Speed through Water) feed to the ARPA for the purpose of Collision Avoidance , the debates around HOW and WHY such action is important , it seems to be leading TO A FIXATION among many young seafarers so much that they seem to be becoming oblivious of the importance of the SOG (speed over ground) Feed to the ARPA !!

Debating often tends to create the Fixated Advocacy of some idea, so much that people begin to judge the purpose and utility of an idea exclusively with respect to what FIXATION they bear in their minds.

The STW Data Feed on the ARPA seems to generate one such incidence. The advocacy of the 'STW Vs SOG' Debate leads, at one point, to discuss the TCPA and CPA. Theoretically, the TCPA and the CPA will not be affected whether a RADAR is fed with STW or the SOG. This condition leads many of the young seafarers into thinking that SOG is a wasted information, and it bears no connection with the calculation of the TCPA and the CPA.

But this is farther from the truth. This is because, there is an INVISIBLE underlying ASSUMPTION  whenever one says that the TCPA and the CPA Data is not affected by the use of STW or SOG, no matter what. The assumption is that Speed and Course of all the ships, Ownship and the Target Vessel, both are constant !!

Once you understand this deceitful assumption, you might be drawn to understand how the SOG feed to the ARPA is essential in order to "judge" the TCPA and CPA .

Notice that quotation marks around the word JUDGE . The word, "Calculate" has been deliberately avoided.

It seems that focus will have to be shifted towards discussing the importance of feeding the SOG to the ARPA in 'judging' the TCPA and the CPA, and also its use in the APRA technology which is handling multiple targets at any single instance.

The single most important reason for why  you would need your ARPA to receive the SOG (Speed over ground) feed from another Equipment, (let us say the GPS) is that you first "judge" whether the target is Stationery or Moving .
Well, Why do you want such a judgement?
Because you would not like to look foolish applying your ROR against a "target" which may later turn out to be a Light house, or a Buoy, or a isolated Rock !

The STW feed to ARPA will not help you realise which object is Stationery and which is moving.
But, Once you have this basic sense , it is now that you begin to judge what ROR you will apply.

Of course you may switch the feed further at your convenience to do the rest.

SOG Feed is needed in the ARPA for Navigation purpose , although not for Collision Avoidance.


I wish to highlight the issue that even SOG Feed has a utility in the determination of risk of Collision.

Let's say, how the SOG helps make distinction between which targets are moving and which are Stationery .

SOG Feed has utility in Trial manoeuvres,

For Determination of Risk of Collision -------> Speed over Ground 

For Action to avoid Collision ---------> Speed Through Water .

Distinction is being made in the two stages

Stage 1 : Determination of Risk of Collision 

Stage 2 : Determination of the Action to avoid Collision.


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