Is Drydocking A Necessary Evil?

By March 10, 2016 Technology No Comments

^ Drydocking Ships is a Mammoth Operation – Image Courtesy of Hydex Solutions at

First in a series of two, this article is based largely on the whitepaper Extending the Interval Between Drydocking to Ten Years by Hydex Solutions.

An Inconvenient Necessity

Drydocking is a bitter pill. But as the owner or operator of a ship, you have to swallow it or you could land yourself in serious financial and legal trouble. Not for nothing does the shipping world regard this procedure as a necessary evil.

Expensive, complicated, lengthy, and stressful is how many will describe it. But as is usually the case, swallowing bitter pills does keep you healthy. Drydocking is no exception. It keeps your ships healthy. And it keeps you out of trouble.

Heavily Fouled Hull  Image Courtesy of Colin Porteous at

Heavily Fouled Hull
Image Courtesy of Colin Porteous at

Fouling and corrosion are the main culprits of hull destruction that force you to drydock the vessel. And because painting hulls shields them from both these marauders, it commands the lion’s share in drydocking operations.

Conventional biocidal and anti-fouling hull coatings are however notoriously non-durable. Plus, they pollute the water around the shipyards where you get your vessel drydocked. But drydock a vessel, you have to. All that you can do is do this less frequently.

This article takes a comprehensive view of the multiple facets of drydocking in order to examine why it gives sleepless nights to many in the shipping industry. In the second article of this series, we look into how to extend the drydocking interval to 10-12 years.

Drydocking Fundamentals

Before we get into the details, let us clarify some things. In the context of this article, hull means all the normally submerged parts of a ship – wetted hull, propellers, rudders, thrusters, bilge keels, stabilizers and the like.

In drydocking, shipyard personnel lift the ship on a dry dock and clean, repair, construct, or maintain its normally submerged portions. Underwater operations have their limitations. It does not always allow efficient inspection, maintenance, and repair of wetted hulls.

Dry docks are narrow basins or containers that can be flooded with water to enable the ship to float inside. Operators can also drain the water from the dry dock to allow the ship to rest on the platform.

Most hulls are made from steel. Engineers also use aluminum, wood, and fiberglass – particularly for small boats or those parts of large ships that need to be more corrosion resistant.

Depending on the type and age of a ship, the legally mandatory interval between successive drydockings normally ranges between 2.5 and 5 years. Classification societies permit ships less than 15 years of age to drydock once every 7.5 years provided they comply with certain criteria.

Corroded Hull Image Courtesy of Pix4Pix at

Corroded Hull
Image Courtesy of Pix4Pix at

And because, we cannot do away with drydocking – we can only extend the interval – a 10-year drydocking interval would be a win-win situation for the shipping industry. How to do this is the topic of the second article in this series.

Rough hulls are the strongest symptom of the need to drydock. Ship hulls face a continuous onslaught of:

  • Fouling due to Marine Organisms
  • Corrosion by Seawater
  • Cavitation from Flowing Water

Corrosion: strong chloride content makes seawater highly corrosive. It causes the failure of as many as 30% of ships and marine equipment. The greater penetrating power of chloride ions and better electrical conductivity makes seawater is more corrosive than freshwater.

Fouling: algae, mussels, polyzoans, seaweed, tubeworms, and barnacles accumulate on the hull and cause fouling. This is a serious phenomenon that can inflate fuel use by as much as 40%.

It also increases the transfer of aquatic species from one area in the ocean to another. Being non native at the destination, the transferred organisms do not have any natural checks. They proliferate rapidly and wreck grave havoc on the local ecosystem.

Underwater Repair of a Major Crack on Hull Image Courtesy of Hydex Solutions at

Underwater Repair of a Major Crack on Hull
Image Courtesy of Hydex Solutions at

Of course, ballast water transfers are the main culprit responsible for the transfer of invasive aquatic species. The prevention of transfer of Non Indigenous Marine Species (NIS) is, in fact, the driving force behind the Ballast Water Management (BWM) Convention 2004.

As of February 11, 2016, 47 countries / parties representing 34.35% of the global merchant fleet tonnage have adopted the BWM Convention. It gets operational 12 months after 30 countries representing 35% of the world merchant fleet tonnage ratify it.

Cavitation: relative motion between ships and water creates its own sets of issues. Flowing water possesses great energy and erodes insufficiently protected hulls through mechanisms such as cavitation – the formation and collapse of low pressure vapor bubbles near the hull surface.

Why is Drydocking Necessary?

Ships, particularly large ones, are intricate floating complexes with a host of equipment systems, engines, motors, pumps, navigational aids, and other mechanical and structural components. Repairs and maintenance are inevitable.

Drydocking minimizes the following deleterious effects of fouling and corrosion (and to a certain extent, cavitation):

  • Drag
  • Hull Damage
  • Fuel Expenditure
  • Emissions
  • Transfer of Non Indigenous Marine Species (NIS)
  • Insurance Costs
  • Penalties for Non-Compliance with Regulations

And because painting takes care of both the potent hull destroyers viz. fouling and corrosion, it is the single largest operation in drydocking. Of course, you have to clean and shot blast the hull before you paint it.

If you do not reblast and recoat a conventional coating system for around 10 years, the fuel penalty i.e. the rise in fuel consumption can shoot through the roof and hit 25-40%.

Fouling and corrosion roughen the hull. This increases drag that, in turn, hikes fuel use. And, any increase in fuel consumption escalates the associated emissions.

Ships Emit 3.3% of the Global Carbon dioxide Image Courtesy of arvydas101 at

Ships Emit 3.3% of the Global Carbon dioxide
Image Courtesy of arvydas101 at

If shipping were a country, it would be the sixth largest emitter of greenhouse gases. It accounts for the 3.3% of the globally emitted carbon dioxide (CO2). Any cut in emissions is more than welcome.

Shipping is a risky business. Bad weather arrives without notice and can ravage your ship. This makes ship insurance very important. And ship owners can get their ships insured for a reasonable premium only if classification agencies provide them a better safety rating.

Now, only well maintained ships will be better rated. This is of course a more immediate concern that makes you opt for drydocking. Because putting off maintenance would entail large and immediate insurance expenses. In the long term, drydocking saves you a lot of money.

Institutions such as the International Maritime Organization (IMO), classification societies, and coastal states lay down standards for the proper construction, operation, maintenance, and repair of different types of ships.

They also establish caps for how much CO2 your ship can emit and how many NIS it can transfer. And yes, they check if you are indeed adhering to these rules. Non compliance can take a heavy toll on your finances and reputation.

For one, they might demote your ship – award it a lower-than-class rating. Or they may declare your ship as unfit for further sailing. They

Monitoring of Underwater Inspection In Lieu of Drydock (UWILD) Image Courtesy of Hydex Solutions at

Monitoring of Underwater Inspection In Lieu of Drydock (UWILD)
Image Courtesy of Hydex Solutions at

can even slap hefty penalties. Not to mention the resulting escalation of insurance costs.

Then again, these institutions make regulations for the method of inspection – a full drydocking or Underwater Inspection in lieu of Drydocking (UWILD). The type and frequency of these inspection methods depends on the age, type-class, and condition of the ship.

Technological advances no longer require you to drydock ships for the following maintenance / repair / replacement operations:

  • cleaning and polishing hulls and propellers
  • welding cracked hulls
  • straightening bent propeller blades
  • replacing bow thrusters
  • dismantling or repairing bow thruster
  • repairing rudders damaged by cavitation
  • fixing or replacing stern tube seals

Now, the purpose of these articles is to discuss the extension of the drydocking interval to 10 years. However, regulatory institutions still need you to drydock vessels at less than 10-year intervals for the inspection, maintenance, repair, or replacement of tail shafts.

The Many Intricacies of Drydocking Image Courtesy of Hydex Solutions at

The Many Intricacies of Drydocking
Image Courtesy of Hydex Solutions at

Because although cutting-edge technology allows us to inspect, repair, maintain, or replace tail shafts less frequently than earlier, we still have to drydock a vessel for these operations – UWILD does not help.

The Intricacies of Drydocking

In the opinion of most guys in the global shipping industry, drydocking is a necessary evil because it is expensive, cumbersome, time-consuming, and stressful. The following reasons make it so:

  • non-availability of the appropriate dock at the right time
  • immense expenditure
  • loss of revenue as the ship is out of service
  • complications in preparing the ship for drydocking
  • possible damage to the ship during drydocking

It is hard to find a yard that offers the necessary drydocking services for your vessel at a location and time of your choosing. You may have such a yard, but it may be located nautical miles away from your ship’s normal route. Or it may be en route but unavailable when you need it.

Ships Plying through the Panama Canal Image Courtesy of BlackMac at

Ships Plying through the Panama Canal
Image Courtesy of BlackMac at

Now, you may be operating your ship on the west coast of the U.S. Most ships normally follow set routes. However, you might have to take your ship to the East Coast for drydocking after crossing the Panama Canal.

Because the yard on the west coast does not offer the services you need. Or because it is fully berthed when you need it. And the larger a ship is, the fewer are the number of yards capable of drydocking it.

Like it or not, you have to start a long journey that may include waiting in queue for crossing the Panama Canal. The fuel you burn now does not fetch any (direct) returns because you are not carrying any cargo.

This effectively means that your expenses rise even as your revenues take a hit. Based on the frequency of useful voyages, every ship earns certain revenue per day. You lose it when you drydock the ship. Of course, this is the short term picture. Drydocking saves more money in the long run.

As for the bill of drydocking, this is a variable amount. It depends on the type / class of ship and the duration and complexity of the exercise. It can run from hundreds of thousands of dollars to around a million dollars.

Preparation for drydocking is a mammoth operation – you have to dismantle numerous pieces of equipment as well as discharge the cargo or passengers. It is not as simple as merely sailing to the available yard.

Face Your Fears Image Courtesy of Gustavo Frazao at

Face Your Fears
Image Courtesy of Gustavo Frazao at

Such preparation is painfully slow and cumbersome. And, it’s not free. Then, you have to provide lodging facilities to your crew for the duration of the drydock. Moreover, the final drydocking bill may exceed the initial estimate as inspection and repair operations reveal hidden defects.

Next, there is the peril of damage to your ship while raising it to the drydock and lowering it later. Ships weigh thousands of tons and such raising-lowering is inherently hazardous. Good yards minimize such risks but (naturally) charge more.


Wise men say the devil is always in the detail. Drydocking is a living example of why and how. Wise men also say you must face your fears. You have to drydock your vessel every once in a while.

But you can minimize the number of times you deal with this nemesis. How? That is the scope of the second article of this series.

Don’t forget to visit our blog loaded with such information rich content.

But if you want to experience how we utilize such knowledge to offer fantastic marine fabrication services, marine pipe fitting, and large scale custom metal fabrication, contact Kemplon Engineering. All you have to do is give us a phone call. We will take over from there.