What is Length Between Perpendiculars: Understanding the Importance in Shipbuilding

When it comes to designing and building ships, there are countless factors that must be taken into consideration. One of the most important of these is the length between perpendiculars (LBP). In this article, we will explore what LBP is, how it is used, and why it is so important in the shipbuilding industry.

Ship size diagram with Length Between Perpendiculars, a graphical representation of the dimensions used to describe a ship.
Ship size diagram with Length Between Perpendiculars, a graphical representation of the dimensions used to describe a ship.

What is the Length Between Perpendiculars or LBP?

The Length Between Perpendiculars (LBP) is measured from the forward-most point of the stem (the bow of the ship) to the aft-most point of the stern (the back of the ship). The forward point, also known as the point of the stem, is located at the very front of the ship, where the bow meets the waterline. The aft point, also known as the point of the stern, is located at the very back of the ship, where the stern meets the waterline.

It’s important to note that the LBP measurement is taken along the waterline and not including the overhanging structures, such as the bow and stern, or the rudder and propeller. These structures are not included in the LBP measurement as they do not contribute to the ship’s displacement.

In addition, LBP is measured perpendicular to the centerline of the ship, it is not measured along the curvature of the hull. Therefore, two perpendiculars are drawn one at the bow and one at the stern and the distance between these two perpendiculars is the LBP.

The LBP measurement is taken from the forward-most point of the stem (the bow of the ship) to the aft-most point of the stern (the back of the ship) along the waterline and perpendicular to the centerline of the ship, not including the overhanging structures.

How is the Length Between Perpendiculars Used?

The Length Between Perpendiculars (LBP) is used in a variety of ways throughout the shipbuilding process. One of the most important uses of LBP is in the initial design phase. By knowing the LBP of a ship, designers can determine the size and capacity of the ship, as well as its overall stability and performance.

In addition to its use in design, LBP is also used in the construction and operation of a ship. For example, LBP is used to determine the size of the ship’s engines and propulsion system, as well as the size and capacity of the ship’s cargo holds. LBP is also used to determine the ship’s gross tonnage, which is a measure of the ship’s overall internal volume. Additionally, LBP is used to calculate the ship’s deadweight tonnage and the deck area, which is used to determine the ship’s carrying capacity and the maximum load it can carry.

LBP is also used in determining the ship’s stability and safety when navigating. The LBP measurement is used in the calculations of the ship’s metacentric height and righting moment, which are important factors in determining the ship’s stability, particularly in rough seas.

Overall, LBP is used in many aspects of shipbuilding, from design and construction to operation, and it is an essential measurement for determining the size, capacity, stability, and performance of a ship.

Where Can You Find LBP?

The Length Between Perpendiculars (LBP) is a measurement that is typically found on the ship’s plans and technical specifications. These plans and specifications are typically produced by the shipbuilder or designer and are used throughout the shipbuilding process. They can also be found in the ship’s registration and classification documents, which are typically maintained by the relevant maritime authority.

In addition, LBP can be found on various online databases and websites that provide information about ships, such as online ship registries, vessel tracking websites, and maritime databases. These websites may have information about a ship’s LBP, along with other technical specifications, such as gross tonnage and deadweight tonnage.

It’s also possible to find the LBP of a ship by physically measuring it, although this is typically only done in certain situations, such as during a ship’s survey or inspection.

Overall, LBP can be found in various sources, including ship plans and technical specifications, registration and classification documents, and online databases. It is also possible to physically measure it, although it is not a common practice.

Why is the Length Between Perpendiculars Important in Shipbuilding?

There are several reasons why LBP is so important in the shipbuilding industry. One of the most important is that it is used to determine the size and capacity of a ship. This, in turn, impacts the ship’s stability and performance.

Another important factor is that LBP is used to determine the ship’s gross tonnage. This measurement is used to determine the ship’s overall internal volume, which is important for determining the ship’s cargo capacity and for determining the ship’s registration and classification.

Finally, LBP is also important because it is used to determine the size and capacity of the ship’s engines and propulsion system. This is crucial for determining the ship’s speed and maneuverability, as well as its overall fuel efficiency.

In conclusion, LBP is a crucial measurement in the shipbuilding industry. It is used in the initial design phase, in the construction and operation of a ship, and for determining the ship’s gross tonnage and capacity. Understanding LBP and its importance is essential for anyone involved in the shipbuilding industry.

The Most Commonly Used Abbreviations are LBP, LPP or PP.

The Length Between Perpendiculars (LBP) is commonly abbreviated as simply “LBP” in the shipbuilding and marine industry. It is also known as “length between perpendiculars” or “length pp” for short.

It is worth mentioning that in some cases, LBP may also be abbreviated as “LWL” which stands for “length on waterline”. This is because LBP is measured along the waterline and not including the overhanging structures, such as the bow and stern, or the rudder and propeller. In some cases, the value might be the same, but there is a slightly different meaning behind LWL. Length on the water means the length of a ship at the level where it sits in the water, so it may include a stern depending on the construction of the ship stern.

To sum up, the most common abbreviation for Length Between Perpendiculars is LBP, also known as “length between perpendiculars” or “length pp”.

Length between perpendiculars