Schooner Kathrina in Dry Dock – Journey Towards a New Sailing Season in Suomenlinna's Historic Dry Dock

For the schooner Kathrina, winter signifies one of the most crucial phases of the year: dry-docking. This is not merely a routine maintenance operation, but a part of centuries-old maritime tradition and an essential prerequisite for the vessel to safely transport passengers in the coming years.

This year, Kathrina will once again be dry-docked at the Suomenlinna dry dock, a place whose history spans nearly 300 years and which is one of Northern Europe's most significant historic dry docks.

Suomenlinna Dry Dock – Over 250 Years of Finnish Maritime History

The Suomenlinna dry dock was built in the mid-18th century as part of the Viapori fortress. Construction of the dock began in 1751, although it was not part of the original plans of the fortress construction director, Augustin Ehrensvärd. Initially, no dock was envisioned for the fortress, but the idea emerged as the needs of the archipelago fleet grew.

A key figure in the dock's design was Daniel Thunberg, whose technical expertise and innovativeness were crucial during the construction phases of the Viapori fortress. Thunberg significantly influenced how the dock was implemented – and the imprint of his work is still visible in Suomenlinna's dock structures.

How the Dock Was Born

The northern part of Susisaari was chosen as the dock's location, where natural formations created a ready-made basin between the main island and the smaller islands to its north. The basin was dammed from the sea with a massive cofferdam. After that, construction began on the main dam between the central islands and filling in the straits to create a tight and drainable basin.

In 1764, the first vessel from the dock was completed: the frigate Hämemaa Oden, designed by the famous naval architect Fredrik Henrik af Chapman. Chapman was one of the leading shipbuilders of his time, whose design philosophy widely influenced shipbuilding activities in the Baltic Sea region. The completion of Oden solidified Suomenlinna dock's position as a significant construction and maintenance site.

The Suomenlinna dry dock still operates on the same principle as in the 18th century – water is pumped out of the basin, and the ship settles onto carefully constructed supports. Only the methods and technology have evolved.

Keel Blocks – The Vessel's Support is Hand-Built on the Dock Floor

Before Kathrina can be brought ashore, a dedicated keel block system is built on the dock floor to support the vessel throughout the dry-docking process.

1. Concrete Blocks

Heavy concrete blocks are placed on the dock floor to form the foundational supports.

2. Wooden Structures

Pre-cut wooden blocks are stacked on top of the concrete blocks. This structure provides a flexible yet sturdy base.

3. Keel Block Line

The wooden and concrete layers form the keel block line, which is precisely shaped to match the vessel's keel line. The keel must be positioned exactly correctly on this line to ensure the ship's weight is safely distributed.

4. Side Supports – “Shores”

Shores, or side supports, are built on both sides of the keel block line to prevent the vessel from tilting when the dock is emptied of water.

The construction of keel block structures is traditional craftsmanship and requires precise expertise.

Preparations on Board – Kathrina Lightened Before Lifting

While the keel block line is being built, Kathrina undergoes its own preparations.
Before dry-docking, the following are removed from the vessel:

• sails

• furniture

• bar fixtures and supplies

• kitchen equipment

• other loose items

This ensures that nothing moves or gets damaged during dry-docking and maintenance work.

Hull Inspection Every Five Years

According to regulations, sailing vessels in passenger traffic must be dry-docked at least every five years, at which time a comprehensive hull inspection is carried out. During this inspection, the condition of the vessel's hull structures, decks, joints, and keel is assessed, and it is ensured that the safety level meets current regulations.

Extensive Repair Work for Dry-docking Year 2025–2026

This year's dry-docking involves exceptionally extensive repair and restoration work, which will strengthen Kathrina's condition well into the future.

Renewal of the Fore Mast

A completely new fore mast will be built for the vessel.

Renewal of the Scantlings (Port Side)

The scantlings will be renewed on the port side, aft to the half deck.

Replacement of Side Planks (approx. 11 planks / approx. 100 m)

In a wooden-hulled vessel, plank replacement is essential. This year, approximately 100 meters of side planks will be renewed by hand.

Renewal of the Port Side Deck

The side deck will be completely rebuilt.

Repair of the Deckhouse

The deckhouse structures and seals will be thoroughly inspected and repaired.

Renewal of the Aft Mess Roof

The roof of the aft mess will be rebuilt, improving the space's watertightness and durability.

Maintenance of a Traditional Sailing Ship is a Cultural Act

Kathrina's dry-docking is much more than technical maintenance. It is part of Finnish maritime cultural heritage, which is preserved only through continuous work and expertise. The work carried out at the Suomenlinna dry dock continues the same tradition that began as early as the 1750s.

When Kathrina is relaunched in the spring, she will once again be ready to transport passengers to the Helsinki archipelago – safely, responsibly, and proudly as part of Finnish sailing ship tradition.