[pedrolourenco]

Originally Posted by ruzbehxyz

The dock water is pumped out using high capacity pumps and gravity. During the process, as the water level goes down, the vessel starts moving down and gradually sits on the blocks, aft / stern area first.

Critical Moment and Critical Period. Brings back memories of Stability Class.

Originally Posted by ruzbehxyz

You can read about Ship Stability online.

Or read Subramanian's books which are easy to understand.

Not sure if I have met you for some course and read your name somewhere on board but you name does ring a bell.

I just finished withe the Dry Dock Specs before signing off last month. Vessel is going to dry dock in a few days.

[ruzbehxyz]

Anti-Fouling paint and the convention

One of the main reasons for Dry-Docking is application of Anti-Fouling paint to the Hull. There is a big process where the Hull is cleaned, blasted, primered etc, before application of the paint. A process which is very important for the vessel.

Ship’s Hull that remain in water continuously are subject to sea growth like barnicles, algae etc, especially when the ship is stationary for long time, thus causing “Fouling” of the hull. This is in turn increase the weight of the ship, makes the movement sluggish, reduces speed and increases the fuel consumption. To prevent this, ships are required to be coated with special paint called “Anti-Fouling” paint, which has evolved over a period of time and also modified to prevent harm to the marine environment.

Background:

While anti-fouling coatings began to be developed from 1840 onwards, the first practical commercial anti-fouling coatings were established around 1860. Over a period of time, these coatings caused harm to the marine environment. Studies have shown that these compounds persist in the water, killing sealife, harming the environment and entering the food chain. One of the most effective biocides for use in anti-fouling paints, developed in the 1960s, was the organotin compound tributyltin (TBT), which has been proven to cause deformations in oysters and sex changes in whelks, as well as longer-term effects due to its persistence and bioaccumulation.

In November 1999, IMO adopted an Assembly resolution that called on the MEPC to develop an instrument, legally binding throughout the world, to address the harmful effects of anti-fouling systems used on ships. The resolution called for a global prohibition on the application of organotin compounds which act as biocides in anti-fouling systems on ships by 1 January 2003, and a complete prohibition by 1 January 2008.

This instrument was later adopted as the International Convention on the Control of Harmful Anti-fouling Systems on Ships.


AFS Convention:

The International Convention on the Control of Harmful Anti-fouling Systems on Ships (AFS Convention), which was adopted on 5 October 2001, prohibits the use of harmful organotin compounds in anti-fouling paints used on ships and establishes a mechanism to prevent the potential future use of other harmful substances in anti-fouling systems. The Convention defines "anti-fouling systems" as "a coating, paint, surface treatment, surface or device that is used on a ship to control or prevent attachment of unwanted organisms".

The Convention entered into force on 17 September 2008.


Source: IMO.


Ships of 400 gross tonnage and above engaged in international voyages (excluding fixed or floating platforms, FSUs and FPSOs) are required to hold an International Anti-fouling System Certificate, for which they shall undergo an initial survey before the ship is put into service or before the International Anti-fouling System Certificate is issued for the first time, and further surveys when the anti-fouling systems are changed or replaced.

Ships of 24 metres or more in length but less than 400 gross tonnage engaged in international voyages (excluding fixed or floating platforms, FSUs and FPSOs) have to carry a Declaration on Anti-fouling Systems signed by the owner or authorized agent. The Declaration has to be accompanied by appropriate documentation to demonstrate that the anti‑fouling system used on the ship complies with the Convention.


For more details on Anti-Fouling paint from Nippon, please read here: https://www.nipponpaint-marine.com/products/a-lf-sea/

[adi.mariner]

Originally Posted by RJK

This looks like chowgule’s yard at Lavgan
I spent 3 months there last year refurbishing one of our oil rigs, must say good for ships and supply vessels but terrible yard for rigs

I was there in July for a couple of weeks. There was a rig undergoing maintenance at that time as well. There were a lot of supply vessels, tugs and mini bulk carriers undergoing Dry Docking. However the spares, OEM technicians and other support has to come from Mumbai which causes delays.

[sukhbirST]

Excellent writeup with great photos. Thanks for sharing, being a naval veteran, have seen this many times and can say that the view down below is really mind blowing. Warships in turn have more equipment like sonars etc which need different expertise and may not coincide with regular drydocks.

[RJK]

Originally Posted by adi.mariner

I was there in July for a couple of weeks. There was a rig undergoing maintenance at that time as well. There were a lot of supply vessels, tugs and mini bulk carriers undergoing Dry Docking. However the spares, OEM technicians and other support has to come from Mumbai which causes delays.

Spares and technicians coming from Bombay is absolutely right. However, scopes such as steel replacement that CLSPL undertakes were so slow, in our case because they would divert their manpower to blasting, painting of the ships. They, in effect, force the contractors to take rigs to Lamprell in Hamriyah if professional work is needed in shorter time. Very sad.

The rig in pic belongs to Jindal Drilling I think.

Cheers!

[ruzbehxyz]

Types of Dry Dock:

1. Graving dock.
2. Floating dock.
3. Marine Rail Dock.
4. Ship-lifts.
5. Marine mobile lifts.

Nowadays, mainly the first two types of dry dock procedures from the above list are used for seagoing vessels.


Blocks Of Dry Dock:


Source: Marine Insight

The blocks inside the dry dock play a critical role in taking the ship’s load and distributing it among the blocks placed below the keel plates. Every ship has a docking plan, that will provide a guide block plan approved by the Ship Classification Society.

The blocks are usually constructed from one material so that their stiffness is similar. If the blocks are built from different materials, the force exerted on the blocks with a smaller elasticity module will squeeze them more than the stiffer block. This can lead to damage to the block or the ship’s hull, as the force distribution will be uneven.

The most common materials used for the blocks are:

1. Concrete with steel.
2. Timber blocks
3. Timber on top and concrete at the bottom

When a timber block is added to a keel track built of blocks with concrete or steel bases, the timber block will take a much smaller load than the others.

Apart from the keel blocks, side blocks are also arranged to support the ship. They are less stiffer than the keel blocks as a stiffer side block will overload the vessel and may damage the structure. The height of the slide blocks is usually similar or more than that of the keel blocks.

Source: https://www.marineinsight.com/guidel...-for-dry-dock/

[BlackBeard]

Originally Posted by arijitkanrar

What about other ships which are not round bottomed?
Are there points on the ship where supports can be attached? Is there weight on the keel of the ship when dry-docked?

What about situations where major refits and overhauls are carried out? For e.g. replacing major machinery where there is a possibility of the CoG shifting considerably. Are additional supports used?

All very valid and interesting questions. I'll see if I can answer some.

In the olden days when ships were much smaller and the bottoms with more curvature the hull used to be shored with strong wooden poles & stakes from the sides to prevent capsizing.

Nowadays with flat bottoms its not that big an issue, however well before the vessel docks its "docking plan" is sent to the shipyard to determine the load bearing members and the bottom blocks are arranged accordingly by the shipyard so that the load is distributed evenly & no deformation of bottom plating occurs. The weight of the ship is indeed on the bottom plating's when she is in the dry dock. The ship also enters the dry dock in her "docking condition" with considerable trim by the stern, the stability is again pre-calculated and advised to the shipyard.

Major refits and overhauls (mostly conversions) are sometimes done while the vessel is afloat except cutting the hull open for obvious reasons. The stability calculations are pre-calculated to prepare for all eventualities.

Originally Posted by srini1785

1. What is the turnaround time between dry docking and back to the sea? how is it charged?

2. How do you test the integrity of the steel (or the material used) in the bottom part (Hull is it called?) ultrasound testing or something?

I suppose that there are limitations on the size of the ships which can come for dry docking.

Dry dock expenses are mostly on the ship owner's account.
The nature and scope of work & type of ship dictates the turnaround time, range from a few days to weeks sometimes even months!

Integrity of the welding is checked by NDT as someone rightly mentioned (ultra sonography testing, dye penetration test). The steel is used is certified & approved by the vessels classification society.

Actually there aren't any limitations to my knowledge, vessels as large as VLCC's dry dock (L 333m, B 60m, 150,000T Light displacement)