Drydocking process explained
Recently I came across a very interesting video, where capt. Jive Turkey explains whole procedure of submarine drydocking. What is great, it all happens on white board and the way it is shown will amaze you. Great job capt. Jive!
Graving dock and floating dock differences
Similar principals apply to drydocking commercial ships.
Ship itself has to be prepared for drydocking as well. For entering graving dock it is requested, that vessel comes on even keel. It means as much as it is possible ship needs to have same draft forward and aft. For entering the floating dock, dock master specifies draft and trim of the vessel. Floating dock doesn’t have to come straight up out of the water. It can be undocked with an angle too. Dock master can adjust it to actual trim and finally leveled with vessel on keel blocks.
For graving dock keel blocks are made out of concrete and are covered on top with hard wood. For floating dock blocks are made out of steel with rubber pads on top. Usually smaller vessels enter into floating docks hence keelblock pressure is smaller. Lowering weight of blocks in floating dock is also important for smooth operation of the dock.
In order to have the keel blocks placed in right position, prior entering the dock, shipyard requires following drawings: docking plan, shell expansion and midship section. All bottom plugs and openings need to be shown there. Yard will keep an eye on it, hence those won’t end up covered by the block. If you have planned steel works on underwater part, that is the right time to inform the yard. They can place the blocks in a way to allow steel works to happen. Removal of keel blocks is possible, but its costly and takes time. Small information will save you time and money.
In both cases the goal is to have as little ballast water in the tanks as possible therefore this condition will allow reduce time for emptying tanks while in the dock and speed up the process of hull washing, blasting and painting. As we know, all clients want to have quick drydocking, noone should compromise safety of that complicated operation. Placing the ship safely on keel blocks has top priority and vessel needs to be ballast according to the document „Ballast condition”. That document is filled up and sign by ship’s crew prior docking. Deballasting by gravity or with pumps may start the moment ship firmly sits on the blocks.