The Docking: Buying the Hull Back

Between dockings a hull only ever gets worse. Every measure in this specialisation so far, trim, the confined-water correction, cleaning between dockings, manages that decline. The docking is the one event that reverses it, and it is the most expensive fortnight in the ship's five-year cycle: dock hire, off-hire, blasting, paint, the propeller, and whatever else was waiting for the water to go away. Yet the specification that decides what the hull will cost for the next five years is usually written by the superintendent and the paint maker's representative, priced by the yard per square metre, and never seen by the person who will have to explain the speed-loss trend afterwards. This course puts that person in the room.

It opens with the docking as a performance event: what a yard visit resets, what it quietly worsens, and the roughness ratchet by which a ship that is only ever spot-blasted arrives at each docking rougher than at the last, and within a few dockings carries about twice the roughness she was built with. Lesson 2 turns roughness into power through the allowance the current ITTC performance prediction method prescribes, the Townsin form, with a worked example the workbook reproduces and the honest limits of a formula fitted to painted hulls of the 1980s. Lesson 3 is the wash: why the high-pressure fresh-water wash comes before any decision about blasting, what water jetting at 700, 1,600 and 2,100 bar does and does not do, and the three facts about it the specification must get right. Lesson 4 is the grades: Sa 1, Sa 2, Sa 2½ and Sa 3 as ISO 8501-1 writes them, the SSPC equivalents, the surface profile that decides whether the coating grips and how much roughness it inherits, and the three scopes every docking chooses between, priced over the cycle rather than over the invoice. Lesson 5 is the coating job itself and the weather it is done in: dew point, humidity, dust and salt, film thickness above the peaks, the inspector, and the out-docking roughness survey that is the only acceptance test worth having. Lesson 6 is the rest of the metal: the propeller grade that pays back in days, the appendages, the anodes, the draught marks, and the performance sensors that get touched at dock and break the record if nobody writes it down. Lesson 7 is the device question: which energy-saving retrofits fit a routine docking, the lead time they need, and the confound that makes a device fitted at the same docking as a fresh coating unprovable unless the comparison is designed before the ship enters the dock. The last lesson is the report card: the two ISO 19030 indicators a docking is judged by, what a post-docking trial can and cannot show, and the docking report that feeds the next specification.

Four required exercises run on one Excel workbook, the docking decision sheet, which turns an in-docking and an out-docking roughness survey into power, prices the three preparation scopes over a whole docking interval with the roughness growth between them, looks a propeller's Rubert grade up into a payback, and computes both docking indicators from monthly speed loss with their intervals. Three subjects are deliberately not taught here, and each is named where it belongs: our Biofouling Management course owns the choice between coating families and the cleaning regime, our Hydrodynamic Energy-Saving Devices course owns what each device can physically recover, and Proving a Device Works owns the evidence hierarchy this course points at a yard invoice.

The opening lesson is free to read as a sample. By the end you should be able to read a yard's surface-preparation clause and say what it will leave under the paint, price the full blast against the spot repair in the only currency that settles it, specify the survey and the sensor log that make the docking measurable, and write the two numbers, a year later, that say whether the money was well spent.