Converted AHTS: cable layer, special personnel and the certificate set
An owner buys a 2011-built, 4,900 GT AHTS (78 m LOA, 1,600 m² open deck, berths for 24) and converts her at a yard. The towing winch and stern roller come out; a 65 t knuckle-boom crane is fitted to starboard, a 40 t stern A-frame is welded to the transom, 380 m² of working deck is enclosed by new weathertight casings to create a cable-handling hall, and the accommodation is extended to 60 berths. The ship keeps her cargo-ship Safety Construction, Safety Equipment and Safety Radio certificates and her existing load line, class is asked to change the notation from AHTS to "Cable Layer", and the owner markets her for "ROV and light cable repair within 50 nm" with up to 30 client technicians embarked. A charterer now offers a 21-day survey job in a neighbouring flag State with 24 technicians plus 22 crew. The technical manager asks whether the ship can sail on her present certificates.
1. Does the ship need a Special Purpose Ship certificate, and what turns on the answer?
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Yes. The trigger is the definition, not the marketing label. Under SOLAS chapter I, a passenger is anyone other than the master, crew, or a person employed in the ship's business; the client technicians are aboard for the ship's business, so they are special personnel, not passengers. The 2008 Special Purpose Ship Code (resolution MSC.266(84)) applies to mechanically self-propelled ships of 500 GT and over carrying more than 12 special personnel. At 4,900 GT and 24 technicians, both thresholds are crossed, and because the ship was built in 2011 the 2008 Code, not the 1983 Code, governs. She therefore needs a Special Purpose Ship Certificate in addition to the cargo-ship Safety Construction, Equipment and Radio certificates, and the technicians must receive the familiarisation and safety instruction the Code requires. She does not become a passenger ship, but the flag must confirm that characterisation in writing. On the present certificates alone she cannot take the charter.
2. What do the enclosed cable hall and the new structures do to tonnage and load line?
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Two separate approvals are missing. First, tonnage: gross tonnage under the 1969 Tonnage Convention is a function of total enclosed volume, and the 380 m² weathertight cable hall is new enclosed space. The 4,900 GT figure is no longer correct, re-measurement is required, and the new GT flows into manning, port fees and any GT-based thresholds. Second, load line: the casings and the A-frame alter the conditions of assignment of the freeboard deck, including openings, air pipes, freeing ports and visibility from the bridge, so the assigning authority (flag or the recognised organisation acting for it) must confirm that the assigned freeboard still holds. The owner cannot keep the old marks because the old certificate exists. Class must also approve the crane and A-frame seatings and the local deck strength, and the notation change from AHTS to cable layer is a class matter, not a flag certificate.
3. Can the 24 technicians simply be added to the crew list for the 21-day job?
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No, and this is the trap in the scenario. The safe manning document is issued for the ship's complement and says nothing about technicians; special personnel must be accounted for separately from crew and from passengers. The LSA capacity and the accommodation must be recalculated against the number actually on board, not against the 60 berths available: 46 persons is comfortably inside the berth capacity, but the lifeboat and liferaft places, the muster list and the emergency plan must all be built around the true total. The technicians must also be given the Code's familiarisation before the ship sails, and the master needs a list of names and locations at all times. Answer: they can sail, but only after the SPS certificate, the corrected tonnage and load line, the class-approved structural work, and a muster and training plan that counts special personnel.