What is Summer Freeboard?

What is Summer Freeboard?

Summer Freeboard is the distance between the uppermost continuous deck i.e. deck line, and the waterline. The larger it is the more reserve buoyancy the vessel has, and the less chance there is of waves breaking over the deck.

It is common to base references to deadweight on what can be carried when a ship is loaded to ‘summer marks’, a ship’s Summer Deadweight DWT, occasionally expressed as Summer Freeboard.

When a DWCC (Deadweight Cargo Capacity) is quoted this is customarily also based on summer marks and a full quantity of bunkers etc. In practice, the DWCC (Deadweight Cargo Capacity) is infinitely variable depending on the weight of bunkers and spares and freshwater on board. Consideration also has to be given to any waste oil and water the ship is carrying since in most parts of the world these can no longer be dumped at sea with impunity.

Load Lines may be referred to as Plimsoll Marks or Plimsoll Lines, after the British politician Samuel Plimsoll who, in the late 19th century campaigned against shipowners who loaded their ships to a depth which jeopardized crew members’ lives. Eventually, in 1890, a system of calculating and marking a safe Freeboard, the distance from the water line to the weatherdeck, was devised and adopted in England, although it was not until 1930 that this finally became international law.

On Plimsoll Marks, there are, in fact, six load-lines. This is because the account is taken of the world’s geography and weather load-lines assessing the hazards of any particular voyage, as well as whether a ship is transiting a salt or, technically safer, freshwater area. The actual load line mark, the disc with a line through it, lines up with the summer load line.

On this Plimsoll Marks, the letters ‘B’ and ‘V’ are related to the Classification Society Bureau Veritas which surveyed the ship to determine the positioning of her marks and thereafter arranged for them to be cut-in and painted on the side of the hull on behalf of the nation in which a ship is registered.

Surplus Freeboard

Load-line Certificates are issued based on the surveyor’s calculations which must follow the rules laid down in the Loadline Convention and without such a document a ship cannot trade legitimately.

Most shipowners prefer the marks to allow the ship to load as deep as possible but there are occasions when a shipowner will opt for a Surplus Freeboard and put the mark slightly lower down on the hull. This might be because the ship will trade to ports where charges are based on summer load-line draughts but the type of cargo envisaged will mean that the ship will never load that deep. Reducing the draught thereby reduces the port costs to be incurred. For example, lumber carriers are granted a second set of load lines for when carrying a deck load of lumber, lumber load-lines, and can sail with reduced freeboard when so laden.

By international agreement, the oceans and waterways of the world are divided into load line zones, either permanent summer, winter, or tropical, or seasonal summer, winter, or tropical, depending upon the prevailing weather conditions likely to be experienced at different times of the year.

Load Line Chart

Load-line zones are displayed on a special Load Line Chart. A ship passing through a summer load line zone can load down to but no further than the top of the summer load line. The same arrangements apply for trading in winter or tropical zones, but extra allowance can be made when trading in what are assumed to be safer freshwater conditions.

Ships with an overall length of 100 meters or less are further restricted when trading in the North Atlantic Ocean in winter. Great care must be taken when planning a voyage to think ahead and to avoid transiting a load line zone when too deeply laden to be able to comply with these international regulations.

In 1982 a new international system of measurement for ships came into force, under an IMO (International Maritime Organisation) resolution. This applied immediately to all new-building ships, and from 1994 all existing ships had to conform to its provisions.

What is Plimsoll Line (Plimsoll Mark) on Ships?

The Plimsoll line, also known as the Plimsoll mark or the international load line, is a reference mark located on a ship’s hull that indicates the maximum depth to which the vessel may be safely immersed when loaded with cargo. This depth varies with the ship’s dimensions, the type of cargo, the time of year, and the water densities encountered in port and at sea.

Samuel Plimsoll, a British politician and social reformer, introduced this line in the 19th century to prevent overloading and enhance the safety of ships. The Plimsoll line has been an integral part of maritime safety rules and regulations ever since.

The line itself is not just a line but a ring with a line through it horizontally. It also has additional lines marked for different sea water types (Fresh Water, Tropical Fresh Water, Salt Water, Tropical Salt Water) and different seasons (Summer, Winter, Winter North Atlantic).

The markings are usually found amidships on both the port and starboard hulls of cargo vessels, and they are used worldwide to ensure that ships have a safe level of buoyancy. They allow captains, loading supervisors, and inspectors to judge if a ship is overloaded as the water level should not be above the Plimsoll line.


What is Surplus Freeboard on Ship?

Surplus freeboard refers to the extra margin of safety provided above the minimum required freeboard in ship design.

To understand it better, let’s start with what “freeboard” is. Freeboard in a ship is the vertical distance from the waterline to the upper edge of the deck side (or gunwale). It’s essentially the distance from the water to the lowest point where water could potentially enter the ship. This measurement is critical for the ship’s safety and seaworthiness, as it helps to ensure that the ship doesn’t take on water and become swamped in heavy seas or poor weather.

Now, coming back to “surplus freeboard,” this is essentially an additional buffer over and above the minimum required freeboard. This surplus freeboard provides extra safety against the ship being swamped. It’s particularly beneficial in situations like rough seas, where larger waves could potentially wash over the deck.

This surplus is not mandatory but serves as a good design practice, providing extra safety and resilience to the ship. The amount of surplus freeboard a ship may have can depend on factors such as the ship’s design, its intended use, and the specific sea conditions it’s expected to encounter.

Surplus freeboard is like an extra safety measure, going beyond what’s minimally required to make a ship seaworthy. It can help ensure the ship remains safe and functional even in challenging sea conditions.


What is Load Line Chart?

In the context of ship chartering and maritime transportation, a Load Line, also known as Plimsoll Line, is a special marking positioned on the side of merchant ships. The Load Line indicates the maximum safe draft, and thus the maximum permissible load, especially pertinent in different seasons and water types (freshwater, tropical saltwater, summer saltwater, winter saltwater, and winter North Atlantic).

A Load Line Chart in this context would therefore refer to a graphical representation that illustrates the relationship between the load (or weight) a ship can carry and the corresponding draft depth, which changes according to the water type and temperature. This would enable charterers, captains, or other interested parties to visually understand how much cargo they can load onto the ship under different conditions.

The Load Line markings and regulations were introduced by the Merchant Shipping Act passed in the UK in 1876, thanks to the efforts of Samuel Plimsoll, a British politician and social reformer. They are also a part of the International Convention on Load Lines, adopted by the International Maritime Organization. The regulations aim to ensure the safety of the ship by not overloading, which might compromise its stability.


What is Summer Freeboard in Ship Chartering?

In ship chartering, the term “summer freeboard” refers to the vertical distance between the waterline and the main deck of the ship, as specified for summer conditions.

Freeboard indicates the safety margin of a ship’s buoyancy. In simpler terms, it tells how much of the ship is above the waterline and how much more cargo it can safely carry without risk of sinking or being overwhelmed by waves. Different freeboard specifications are given for different seasons, as the seaworthiness of a ship is affected by changes in water density and weather conditions that occur across different seasons.

The summer freeboard is based on summer seawater conditions, which typically have higher temperatures and lower densities than in winter. Therefore, the summer freeboard is typically less than the winter freeboard because a ship can safely be deeper in the water during summer conditions.

The International Load Line Convention, also known as the Plimsoll Line, governs these measurements and markings, with standards set for different seasonal and geographical conditions.

Please note that the ship’s freeboard can impact chartering decisions as it can dictate the vessel’s cargo carrying capacity. This means that a ship with a smaller summer freeboard might be able to carry more cargo in summer conditions, which could potentially mean a higher income for the charterer. Therefore, understanding freeboard, including summer freeboard, is a crucial aspect of ship chartering.


What is the Plimsoll Mark (Load Line) regulation?

The Plimsoll Mark, also known as the Load Line, is a regulation that relates to the safety of merchant ships. It sets the minimum criteria for the safe loading of vessels to prevent them from becoming overloaded and risking sinking.

The regulation was developed in the 19th century by a British politician named Samuel Plimsoll. He was concerned about the loss of ships due to overloading, which was a common practice by unscrupulous ship owners trying to maximize their profits.

A Plimsoll mark is a line painted on the hull of a ship which indicates the maximum depth to which a ship can be safely loaded, or the minimum freeboard (distance from the waterline to the main deck) that must be maintained. It’s represented by a circle intersected by a horizontal line with further horizontal lines (seasonal load lines) marked from it. The actual position of these lines varies with the ship’s size, type, and design.

The load lines mark different safe loading levels depending on geographical location and time of the year, due to variations in seawater density and weather conditions. These include:

  1. TF (Tropical Fresh Water)
  2. F (Fresh Water)
  3. T (Tropical Seawater)
  4. S (Summer Temperate Seawater)
  5. W (Winter Temperate Seawater)
  6. WNA (Winter North Atlantic)

These rules have been adopted internationally through the International Convention on Load Lines, administered by the International Maritime Organization (IMO), and are subject to regular review and updates to ensure they remain relevant and effective. In many countries, it is against the law to set sail if the ship is loaded beyond its Plimsoll line.

What is the measurement of Plimsoll Mark (Load Line)?

The Plimsoll mark, also known as the load line or waterline, is a reference mark located on the ship’s hull that indicates the maximum depth to which the ship can be safely loaded with cargo.

The measurement of the Plimsoll mark is not a singular fixed value. Instead, it varies depending on several factors such as:

  1. The ship’s size and type.
  2. The season of the year. For instance, seawater density varies between summer and winter, affecting a ship’s buoyancy. Therefore, there are separate ‘summer’ and ‘winter’ load lines.
  3. The geographical area in which the ship will be operating. Freshwater load lines may be different from saltwater ones, due to differing water densities.
  4. Whether the ship is venturing into tropical or cold water areas. There are separate ‘tropical’ and ‘winter North Atlantic’ load lines.

Hence, the Plimsoll mark consists of several lines indicating these different load conditions, each labeled for easy identification: TF (Tropical Fresh Water), F (Fresh Water), T (Tropical Seawater), S (Summer Seawater), W (Winter Seawater), WNA (Winter North Atlantic).

The actual “measurement” of the Plimsoll mark, in terms of distance from the water’s surface to the bottom of the ship (the ship’s draft), is not a universal figure but rather specific to each ship and its loading condition.

This mark is vitally important as it ensures that ships do not exceed their safe loading limit, which could result in decreased stability and potentially catastrophic accidents. It is mandatory for all sea-going vessels to have this mark under international maritime law.


How do you calculate Load Line (Primsoll Mark)?

The Plimsoll line (also known as the Plimsoll mark or the international load line) is a reference mark located on a ship’s hull that indicates the maximum depth to which the vessel may be safely immersed when loaded with cargo. This line makes it easy to determine whether a ship has been overloaded.

The Plimsoll line is actually not a single line, but a series of lines, each marked for a specific type of water (fresh, salt, warm, cold) and load conditions (summer, winter, tropical, etc.). The ship’s load varies with the season and the water density, and these details are taken into account.

Calculation of the Plimsoll line is a complex process which involves the assessment of many aspects of the ship’s structure and design, including:

  1. Ship’s Weight: This includes the weight of the ship’s structure, equipment, crew, passengers, provisions, etc.
  2. Ship’s Buoyancy: This is the volume of water displaced by the ship when it is immersed to the Plimsoll line.
  3. Load Weight: This is the weight of the cargo, fuel, water, and other loads that the ship will carry.

In order to calculate the position of the Plimsoll line, you need to balance the ship’s weight and its buoyancy, according to the principle of flotation. This principle, also known as Archimedes’ principle, states that an object (in this case, a ship) immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object.

Once these aspects have been thoroughly assessed, the Plimsoll line can be drawn on the ship’s hull. It should be noted that the calculation and placement of these marks is usually performed by naval architects and marine engineers, using detailed ship plans and complex calculations.

In practice, this is heavily regulated. The International Convention on Load Lines, adopted by the International Maritime Organization, sets the rules which have been internationally agreed upon for the safety of life at sea, including the placement of the Plimsoll line. As such, for a ship to be seaworthy, it must have its Plimsoll line correctly marked in compliance with these regulations.


The Story of Samuel Plimsoll and the development of the Load Line Rules

Samuel Plimsoll was a British politician, social reformer, and later on, a maritime safety pioneer, known for the creation of the Plimsoll line, also known as the Plimsoll mark or the load line.

Born in Bristol in 1824, Plimsoll embarked on a number of entrepreneurial ventures before entering politics. However, it was his empathy for the seafarers and his dismay at the appalling conditions they faced that ultimately defined his legacy.

In the mid-19th century, the maritime industry was notorious for its dangerous conditions. One particular practice known as “coffin ships” was especially concerning. Unscrupulous ship owners would often overload their old, often unseaworthy ships with cargo to maximize profit, with little regard for the safety of the crew. Many of these overloaded ships would sink in rough seas, leading to the tragic loss of lives.

As a member of Parliament in the 1870s, Plimsoll dedicated himself to addressing this issue. He worked tirelessly to introduce new legislation to improve the safety of seafarers. In 1872, he published a book titled “Our Seamen,” which highlighted the inhumane conditions faced by the sailors and drew public attention to the problem of “coffin ships.”

The culmination of Plimsoll’s efforts was the Merchant Shipping Act of 1876. This Act gave the British Board of Trade the power to inspect ships and determine whether they were seaworthy. More importantly, the Act introduced the concept of a “load line.”

The load line, which became known as the Plimsoll Line, was a marking on the side of merchant ships. It indicated the maximum safe load a ship could carry under varying sea conditions. If the line was submerged, it meant the ship was overloaded and risked sinking. The Plimsoll Line was an ingenious yet straightforward solution to a problem that had claimed many lives.

The Plimsoll Line became internationally adopted and is still in use today. Ships have a series of load lines for different sea conditions (tropical, summer, winter, and so on), taking into account factors like water density and temperature.

The work of Samuel Plimsoll was instrumental in improving the safety of seafarers and revolutionizing maritime safety standards. His tenacity and passion for reform saved countless lives and left a lasting legacy in the maritime industry. The “Plimsoll Line” remains a universal symbol of his efforts to ensure the safety and welfare of seamen worldwide.

Where and how should Load Lines (Primsoll Marks) be marked?

Load lines, also known as Plimsoll marks, are markings on the hull of a ship that indicate the maximum depth to which the ship may be safely loaded, i.e., how deeply it can be immersed in water. Load lines take into consideration the specific conditions of water (e.g., saltwater is denser than freshwater, and cold water is denser than warm water), which will affect the ship’s buoyancy. The ship’s construction, specifically the level of its freeboard (the distance from the waterline to the main deck), also impacts the load line.

Here are the general guidelines on where and how these load lines should be marked:

1. Location of the Marks:

The marks should be placed amidships, on both sides of the ship. Amidships refers to the middle area of a ship in terms of length and width.

2. Components of the Mark:

The Plimsoll mark comprises several components:

  • The circular disk or ring: It is 300 millimeters (approximately 12 inches) in diameter.
  • The horizontal line: Passing through the center of the ring, this line is 25 millimeters (1 inch) wide and 450 millimeters (18 inches) long. This line signifies the summer load line in saltwater and is also known as the Plimsoll Line.
  • Seasonal load lines: These are additional lines marked around the ring indicating permissible loading levels for other seasons and water types. They include TF (Tropical Fresh Water), F (Fresh Water), T (Tropical Salt Water), S (Summer Salt Water), W (Winter Salt Water), and WNA (Winter North Atlantic).

3. How to Mark:

These marks should be permanently painted and easily visible. The baseline of the marks (the upper edge of the line passing through the center of the disk) should coincide with the assigned summer load line.

4. The Line for the Worst Condition:

The Winter North Atlantic (WNA) load line is the lowest permissible load line, providing the highest freeboard and thus the highest safety margin. This line is for ships that might need to cross the North Atlantic in winter, where they might encounter severe weather conditions.

Remember, these lines are subject to regulatory oversight. In many nations, the local maritime authority or an international body like the International Maritime Organization (IMO) will provide specific guidelines and conduct inspections to ensure compliance. The Load Line Convention of 1966 (and its updates) provides internationally agreed-upon rules for load lines.


How would you explain Summer Load Line (Pimsoll Mark)?

The Summer Load Line, often called the Plimsoll Line, is a reference line found on a ship’s hull that indicates the maximum depth to which the vessel may be safely loaded with cargo and passengers during the summer months. It is part of the load line marks (also known as Plimsoll marks) that are used to ensure that a ship has sufficient freeboard (the height of the ship’s side between the waterline and the deck) and thus sufficient buoyancy to prevent sinking.

Here’s how you might understand the Summer Load Line:


The Summer Load Line is part of the load line marks and is located amidships, on both sides of the ship. This is typically the middle area of a ship in terms of length and width.


It’s usually represented as a horizontal line passing through the center of a ring (also called the Plimsoll Ring). The ring is 300 millimeters (approximately 12 inches) in diameter, and the line is 25 millimeters (1 inch) wide and 450 millimeters (18 inches) long.


When the ship is loaded, the water should reach no higher than the line. If the water is over the line, the ship is considered overloaded and could be in danger of sinking, especially in adverse conditions.

Seasonal Variation:

The “summer” designation refers to the warmer months of the year when the water is typically warmer. Warm water is less dense than cold water, which means a ship will sit lower in the water in warm conditions compared to colder ones, even if the load is the same. Hence, the load line for summer ensures the ship remains safely above water during these warmer months.

Other seasonal and geographical marks are used as well for different conditions: TF (Tropical Fresh Water), F (Fresh Water), T (Tropical Salt Water), S (Summer Salt Water), W (Winter Salt Water), and WNA (Winter North Atlantic).


This mark and the regulations associated with it are internationally agreed upon under the International Load Line Convention of 1966, overseen by the International Maritime Organization (IMO). This ensures that all seafaring vessels maintain a consistent and safe standard.

It’s important to note that these lines are subject to regulatory oversight, and improper use could lead to penalties. Always consult your local maritime authority or appropriate body for the most accurate and legally binding information.

Do all ships have a Plimsoll Mark (Load Line)?

Virtually all large commercial ships have Plimsoll Marks or Load Lines. These markings are a critical safety measure and are required by international law under the International Load Line Convention of 1966, overseen by the International Maritime Organization (IMO).

The convention applies to ships that are engaged in international voyages and have a length of 24 meters or more. These marks show the maximum depth to which a vessel may be safely loaded with cargo and passengers, considering factors like the season, the water’s density, and the geographical area in which the ship will be sailing.

However, certain types of ships, like warships, fishing vessels, yachts, or ships navigating exclusively in shallow waters, might be exempted from the requirements of this convention and may not have Plimsoll Marks. Still, even in these cases, it is not uncommon to find such marks as they provide a useful visual guide for loading and the ship’s safety.

Always remember, the application and adherence to the regulations regarding load lines depend on national legislation and the nature of the ship’s service, and it’s always best to refer to local maritime authorities for the exact requirements.