As a newbie to sailing, the sailboat specifics can be overwhelming. Taking time to familiarize yourself with the measurements and vocabulary associated with boats will allow you to be more informed about boats and know which type is right for which activity. You’ll be a better sailor and boater with this knowledge.
LOA – Length Overall
Length Overall (LOA) is the most common measurement used to describe the size of a sailboat. It refers to the total length of the vessel, from the tip of the bow (front) to the aft end of the stern (back).
LOA is typically measured in feet or meters. This measurement can be useful when comparing boats of similar types, as it gives you an idea of the overall size.
LOD-length on deck
LOD, or Length on Deck, is the measurement of the boat from the tip of the bow to the stern along the deck.
This length does not include any spars, bowsprits, antennas, etc. that are mounted above the main deck.
The difference between LOD and LOA (length overall) is that LOA takes into account any protrusions such as spars and bowsprits. LOD may be shorter than LOA sometimes.
LWL – Load Waterline Length
The LWL or Load Waterline Length is the measurement of the length of a boat at the point where it touches the water.
It is the length of the boat that makes contact with the water and is often shorter than the overall length (LOA) due to the curvature of the hull.
The LWL plays an important role in determining the performance of a sailboat; for example, a longer LWL can help increase stability and reduce drag, allowing the boat to move more efficiently through the water.
The LWL also affects the size of the sail area needed to power the boat. As such, boats with a longer LWL will require larger sails to generate adequate power, while boats with a shorter LWL may need smaller sails.
Beam – The width of the boat
The beam of a sailboat is the maximum width of the hull and is an important measurement for sailing performance.
A wider beam provides more stability on the water and increases the overall sail area. Having a larger sail area will help to increase speed and maneuverability in windy conditions.
It’s important to consider the beam of the boat when deciding what type of sails to use. A boat with a wider beam will require bigger sails, while a boat with a narrower beam will require smaller sails.
Draft – The depth of the boat in the water
Draft measures the distance from the waterline to the lowest point of the boat’s hull when it is fully loaded.
This is important because it affects the boat’s maneuverability, stability, and performance in different sea conditions.
It also affects the sail area of the boat, since a greater draft can provide more stability and lift, allowing for larger sails to be used. Shallow draft boats tend to be able to get into shallower waters than those with deeper drafts.
Full keel vs. modified keel vs. fin keel
The three main types of keels are full, modified, and fin keels.
Full keels are the oldest and most traditional type of keel. They are typically found on heavier displacement boats such as cruisers and larger sailboats.
Full keels provide more stability due to their size and weight, but also create more drag, which can slow down the boat.
Modified keels are a hybrid between full and fin keels. They are often used on boats with moderate displacement, meaning they have a moderate amount of weight.
Modified keels provide a good balance of stability and speed due to their shape and size.
Finally, fin keels are usually found on lighter displacement boats such as racing and performance sailboats.
Fin keels have the least amount of drag, allowing the boat to move faster, but they are not as stable as full or modified keels.
Displacement – The weight of the boat
The displacement of a boat refers to the total weight of the boat, including all of the materials used to construct it. It is usually measured in either metric tonnes or long tons.
The type of displacement your boat has will depend on its size and purpose, with light displacement boats usually being used for day sailing and racing, while moderate and heavy displacement boats are better suited for coastal and ocean cruising.
Light displacement boats are typically quite lightweight, with a hull weight of around 2 tonnes and a total weight of 4 tonnes or less.
These boats are often very fast and agile but can have limited load-carrying capacity due to their light construction.
Moderate displacement boats typically weigh between 4 and 10 tonnes, with a hull weight ranging from 3 to 8 tonnes.
These boats are best suited for coastal cruising and are usually made from heavier materials than light displacement boats. This makes them able to carry a greater load and handle rougher seas with more confidence.
Heavy displacement boats weigh more than 10 tonnes, with a hull weight of up to 15 tonnes.
These boats are built for long-distance ocean cruising and are designed to be sturdy and reliable even in heavy weather. As such, they are usually made from stronger materials than other types of boats and have a much larger load-carrying capacity.
D/L or DLR ratio- Displacement to length ratio
Displacement to length ratio (DLR) is a calculation used to measure the size of a sailboat.
It is determined by dividing the displacement (the weight of the boat) by the waterline length (the length of the boat that is in contact with the water when it is afloat).
The result of this calculation, also known as the DLR, can be used to compare different types of boats or to determine which type of sailboat is most suitable for specific conditions.
The formula for calculating the displacement-to-length ratio is:
DLR = (Displacement/2240)/(0.01xLWL)^3
Displacement in pounds, LWL is Waterline Length in feet
Generally, sailboats with higher DLRs tend to have a more rounded hull shape and are better suited to deep-water sailing in heavy weather conditions.
Sailboats with lower DLRs tend to have a more slender hull shape and are better suited to shallow water sailing in light weather conditions.
Ballast
Ballast is the weight of the boat that is not part of the boat’s structure. This weight can come from a lead, water, or other materials, and it is located in the bottom of the boat to help keep it stable in the water.
The amount of ballast affects the sail area, as more ballast will lower the sail area while decreasing ballast will increase the sail area.
This is because when there is more ballast in the boat, it will be pushed down into the water which reduces the area that a sail can reach. On the other hand, decreasing ballast will allow a sail to extend further.
Ballast is also important for maneuverability and stability; too much ballast and the boat will be sluggish and difficult to turn, while too little ballast could cause the boat to be unstable and even capsize.
Balancing the amount of ballast is key to achieving optimal performance for any type of sailboat.
CSF-Capsize screening formula
The capsize screening formula is a calculation that provides a good indication of the stability of a sailboat. It is the ratio of a boat’s displacement (weight) to its Beam (width).
Capsize ratio formula: Beam / ((Displacement/64.2)1/3)
The beam is in feet. Displacement is in pounds
A good capsize ratio is generally considered to be between 1.33 and 2.0, although this can vary depending on the type of boat and its purpose.
A lower capsize ratio indicates that the boat is more stable, as it will be less likely to tip over in strong winds or waves. A higher capsize ratio indicates that the boat is more prone to capsizing.
Motion comfort ratio
Motion comfort ratio (also referred to as “Ted Brewer” ratio) is a measure of the overall stability of a sailboat.
Generally, a boat with a motion comfort ratio greater than 40 is considered stable and a boat with a motion comfort ratio less than 30 is considered unstable.
A boat with a motion comfort ratio between 30-40 is considered moderately stable. The higher the motion comfort ratio, the more comfortable the boat will be in rough waters.
Ted Brewer’s CR formula is: Displacement in pounds/ (.65 x (.7 LWL + .3 LOA) x Beam1.333).
For instance, a boat with an LWL of 35 ft and a displacement of 10,000 lbs would have a motion comfort ratio of 37.5. This would indicate that the boat is moderately stable and should provide an adequate level of comfort in rough waters.
The motion comfort ratio was developed by Ted Brewer and has been used for many years as an indication of a boat’s stability.
It is important to keep in mind, however, that this ratio alone cannot give an accurate picture of how stable a boat is. Other factors such as hull type and keel type should also be taken into account when assessing a boat’s stability.
Ballast to displacement ratio
The ballast-to-displacement ratio is a measure of how much ballast is needed in relation to the weight of the boat.
The higher the ballast-to-displacement ratio, the more stable the boat will be and the less likely it will be to capsize.
the ballast-to-displacement ratio is important for ensuring the boat is adequately balanced and has good performance when sailing.
It is especially important for boats that have large sail areas, as larger sail areas require more ballast to keep the boat steady.
When considering a boat’s ballast-to-displacement ratio, keep in mind that a ratio of 40-50% is generally considered to be optimal. Any higher than that may be too much, while any lower may not be enough.
