This subject has been debated at many levels, for many years, by many people and no definitive answer has yet been reached!

The purpose of this paper is to examine the various merits of both systems and to attempt to record some of the key conclusions reached by others.

Further inputs and comments are most welcome as the intention is that this web-site should be interactive and serve as a centre for the exchange of information.

The basis of the debate is the interpretation made on the original I.M.O. Performance Standards laid down for Voyage Data Recorders (VDR) A.861(20) dated November 1997.

Here, the following Purpose and Operational Requirements were stated:-

As defined in the I.M.O Performance Standards: "The purpose of a voyage data recorder (VDR) is to maintain a store, in a secure and retrievable form, of information … "

The final recording medium should be installed in a protective capsule which should meet all of the following requirements:

be capable of being accessed following an incident but secure against tampering

maximise the probability of survival and recovery of the final recorded data after any incident

These clauses were then further clarified by the I.E.C. (International Electrotechnical Commission ) in the preparation of their Technical Specification and Test Standards. I.E.C. 61996 dated 1999.

During the preparation of this Standard, it became clear that there was no definitive interpretation of the term "maximise the probability of survival and recovery".

The Technical Committee was made up of a unique panel of experts with differing backgrounds.

In view of the comparative infancy of maritime "black boxes" , representatives from the aircraft industry were invited and encouraged to attend.

Their experience, spanning over twenty five years, proved invaluable in determining many of the standards necessary for adoption by the marine industry.

In general, their view of "maximising the probability of survival" was firmly in favour of a rugged fire-proof capsule which would remain with the vessel in the event of sinking.

When challenged on the recovery from a sunken wreck at depths the Committee were reminded of the successful recovery of the black box flight recorder fitted to the Air India Boeing 747 which crashed in the deep trench in the North Atlantic, off Ireland.

Clearly this demonstrated that such a recovery could be achieved but estimates of the cost varied from very high to extreme.

Nevertheless, the proponents of the fixed capsule pressed their case and concluded that the capsule should remain with the largest part of the casualty, meaning the vessel itself. Even if the acoustic beacon is no longer operating, then location of the wreck should be possible.

Others, who favoured the "float-free" approach , claimed that recovery would be at a fraction of the cost of the fixed version and would enable a far speedier availability of the data. They suggested that technology used in existing E.P.I.R.Bs could be developed to provide such a solution .

E.P.I.R.B s ( Electronic Position Indicating Radio Beacons ) have been in existence for some twenty years and are designed to transmit a signal , when activated , via satellite . These signals can be interpreted to provide accurate position information to search and rescue services . More recent models include G.P.S ( Global Positioning System ) information which is fed to the unit’s internal memory for subsequent transmission .

After much debate, specifications and test methods were drawn-up for both solutions, largely developed from the existing aircraft industry’s standard referred to as ED 56A.

Concerns continued to be expressed regarding the effect of heat on the radio transmission device contained within a standard E.P.I.R.B. with the result that the final specification insisted that the float-free mechanism be inhibited if the fire exceeded the fire survivability of the transmitter.

Another stringent requirement, again adapted from the aircraft industry, was that of a penetration test. Whilst the severity of the aircraft specifications were reduced for the perceived marine environment conditions, the rest ruled out most, if not all, E.P.I.R.B.s currently in production at that time. As a result, it is believed to be a truism that no VDR manufacturer offers a float-free option.

With a Performance and Technical standard in place, attention was then turned to the introduction of VDRs into the world’s maritime fleet. Whilst international agreement was reached for fitting in new vessels and existing passenger carrying vessels, legislation fell short of including existing cargo ships.

The Maritime Safety Committee (MSC) of the International Maritime Organisation (I.M.O.) instructed its delegates to carry out a feasibility study on the carriage of Voyage Data Recorders (VDR) on existing cargo ships.

It was as a direct result of this study that the concept of a Simplified Voyage Data (SVDR) was adopted.

The purpose of this simplified version was to provide the marine industry with an interim solution to the inclusion of some form of voyage data recording on older vessels, which may be equipped with diverse equipment, not readily suited to conversion to an external recorder.

One of the key decisions reached, of direct relevance to the fixed versus float-free discussions, was that the penetration test should be omitted for SVDR and a relaxation of some of the environmental tests. This made the use of an E.P.I.R.B. type device a far more practical proposition than was the case with VDR.

As a result, work is well advanced with experienced E.P.I.R.B. manufacturers in the design and construction of a float-free device. However, it should be remembered that such a unit only represents part of a complete SVDR system.

Most reputable SVDR system manufacturers offer both a fixed or float-free option to maximise the probability of survival and recovery of the final recorded data captured .

The philosophy being to allow the customer to make their own choice. To assist in the decision making process and with the background to the subject now established, a number of points have been recorded and abstracted from papers presented or published over the past three years.