What Is Freeboard On A Boat?

What Is Freeboard On A Boat?

Freeboard is a ship’s/boat’s measurement from the waterline to the upper edge of deck plating at the side, and it’s important for safety. If you don’t have enough freeboard, your boat may not be safe to sail in certain situations or conditions.

Freeboards are measured in inches or centimeters, depending on what country you live in. They are usually included in a boat or yacht’s specifications.

Freeboard draft keel of a boat
Freeboard, draft and keel of a vessel/ Image: Boat Ed

Understanding the basics of freeboard is important for any boat owner. Vessels are required by law to have load line marks that indicate their maximum allowable draught under specified conditions (geographical and seasonal).

It’s also worth knowing what draft means so you can compare it with your own measurements. The draft is simply how far below the waterline an object sits when in waters.

Why would someone need to know the freeboard of their boat

Freeboard is extremely important because it protects the boat’s structure and its contents. If your freeboard is too low, waves or swells could easily capsize or swamp your boat when out at sea. This would be very dangerous for passengers and crew, not to mention costly to repair.

On the other hand, if your freeboard is too high, this could also be dangerous, especially if the boat is loaded with cargo or passengers. It could also affect the dynamic performance of the boat and create resistance in the water that uses up valuable power from its engine.

The consequences of low freeboard

You wouldn’t want your boat to sink or become less maneuverable, so it’s important you understand what the consequences of low freeboard are. If your boat doesn’t have enough freeboard, heavy waves or wind could fill it with water and sink the vessel. This is a serious problem because it could risk lives or severely damage the vessel.

Low freeboard also means that although the boat has enough space to take on passengers or cargo, it could lose stability when the vessel becomes flooded.

Why does it matter how high the freeboard is

The height of a vessel’s freeboard is important because it ensures the boat can ride over rough seas and survive waves without sinking. If your boat has a low freeboard, it may have trouble with waves that are too high for it to handle safely.

And, too high is just as bad, because it can create undesirable resistance in the water. It requires a lot of power to simply push the vessel through the water when it has too much freeboard. Generally, this means more fuel is used and your boat would never go as fast or be able to travel the same distance in the same amount of time.

Since freeboard is essential for your boat, ensure that it always has enough of it to be safe.

What is a safe freeboard?

The best way to determine the correct freeboard for your boat is on a vessel’s load line certificate. Safe freeboard is the minimum distance between your boat’s uppermost deck and the waterline, which you can use to prevent it from sinking after extreme weather.

Safe freeboard is determined by the weight of your boat when empty, fully loaded but still afloat, with maximum crew/passenger capacity. What this means is that your boat always has to have more space for cargo or people than what you are carrying at that moment.

It depends on the vessel’s size and load capacity. Once you know the load capacity of your vessel, you can adjust the waterline to make sure it has enough freeboard and stability.

How to check your boat’s freeboard level 

The load line mark should always be visible on your boat, even if it’s covered with water. You can use a measuring tape to see how high your vessel is above the surface of the water. To measure the distance between the uppermost deck and waterline, go from bow to stern and take a reading at both ends of the boat.

What is the difference between draught and freeboard?

The draft is how deep an object sits in the water. It’s easy to confuse this with freeboard, but they are completely different.

Draught refers to the depth of an object like a boat below the waterline, while freeboard refers to the height of the boat’s uppermost deck.

Boat’s depth = Draught + Freeboard

So, Freeboard = Depth – Draught

Boat terminology
Boat terminology/ source: pages.nxtbook.com

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