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How are Boats Measured?

A wakeboard boat at a wooden dock on a sunny day.

At a first glimpse, it seemed that the task of measuring the length of a boat would be relatively straightforward.

The reality is that there are a variety of ways to measure boats – it all depends on the information needed and the intended use of this measurement.

How to Measure a Boat

Measuring The Length

The length of the boat is measured by a straight line that extends from the tip of the boat’s bow to the stern or the rear of the boat. Rear platforms or deck extensions may or may not be included in this boat length measurement, depending on the purpose of the measurement. However, in most cases, fittings and outboard motors should be excluded from the measurement.

The Length Of The Boat Determines Relevant Laws.

State and federal laws mandate certain safety equipment be placed onboard a boat. Safety and other requirements are categorized into four primary classes

  • Class A – boats that are less than 16 feet in length.
  • Class 1 – boats that are more than 16 feet in length but less than 26 feet.
  • Class 2 – boats that are more than 26 feet in length but less than 40 feet.
  • Class 3 – boats that are more than 40 feet in length but less than 65 feet.

Those boats that are longer than 65 feet – with a weight that does not exceed 300 gross tons are considered Small Research Vessels (SRV).

Measuring The Beam

A beautiful view from a bow of yacht at seaward.

This is the measurement at the widest part of the boat, with a name that is a throwback to how wooden boats used to be built. It is often somewhere near the middle of the boat.

The beam’s technical measurement is the distance between the outer points of the ship’s extremities. Knowing the measurements of the beam helps a boat operator safely navigate obstacles in the water or through narrow passageways.

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Pro-Tip – When you have the measuring tape in your hand, take a few measurements to ensure you have measured the widest point of the boat.

Measuring The Height

The height of your boat is measured from the boat’s keel (its backbone or main structural component) that runs along the center of the boat from the tip of the bow to the stern. The height is the distance between the keel and the boat’s highest point. This is important information for sailboat operators who are negotiating bridges and areas with height restrictions.

The Load Water Line

Landscape photo of speed boat on the sea with sky natural beauty.

This is the boat’s length as it sits on the water. Everything that is located below the load water line is beneath the water’s surface.

Pro-Tip – When measuring, keep the tape measure in a straight line – down the boat’s center. I was tempted to bring the tape measure around the hull – which would NOT provide an accurate length. The fundamental key to the measurement is that it is obtained using a straight line without being skewed.

Basic Boat Categories

A photo of sailboat in the sea in the evening sunlight over beautiful big mountains background.

Watercraft vessels are categorized based on the length of the boat. There are four types of boat categories, as follows – A pleasure craft with a length of 6 meters or less.  A ‘pleasure craft’ is any type of boat or ship that is utilized for recreation or pleasure exclusively. These might include the following –

  • Sport Fishing Boats – A fishing ship used on rivers, lakes, and the ocean.
  • Cabin Cruisers – these boats can cruise greater distances, which is why they usually have living accommodations onboard.
  • Bowriders – often called family boats, bowriders are versatile boats with offset helms. They perform well at high speeds and are great options for tow-watersports.
  • Pontoon or Tube Boats – a boat that is designed to stay afloat using floats. A catamaran is an example of a pontoon boat.
  • Sailboats – a boat that is propelled by sails – either entirely or partially. There are a variety of sailboat types within this category. For example, a cutter, a schooner, a sloop, or a yawl, among others.
  • Deck Boats – like a bowrider but has more space.
  • Surf Boats/Wakeboard Boats – developed to create specific wakes that allow for aerial tricks by a wakeboarder.
  • Houseboats – a boat used as a home. Often, they are moored and connected to utilities on land.
  • Paddle Craft – is a non-motorized boat. Paddle crafts are available in several varieties, like a canoe or kayak.
  • Personal Watercraft (PWC) – is a small watercraft with an inboard engine that uses a jet-propulsion system to move the boat forward. Personal watercraft have unique handling aspects due to their size.  For example, personal watercraft can only be steered when the throttle is engaged.  Technically not considered a boat.
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However, if a vessel of any size is used to move passengers or merchandise – for profit, it is considered a commercial boat – which comes with a large boatload of commercial regulations and rules. Plus, these boat categories –

A pleasure craft with a length of 6 meters or more. An example of a large pleasure craft would be a yacht. Yachts are further categorized into Mega Yachts, Super Yachts, and Charter Yachts. A non-pleasure craft with a length of 6 meters or less and those greater than 6 meters.

Here is an example of a non-pleasure craft that is longer than 6 meters –

When I first started boating, I heard other boat operators using what seemed like random numbers to describe their boats. To my surprise, the numbers were not random but a code with a specific meaning. For example-

  • A boat with a 1430 description is 14 feet long and 30 inches wide.
  • A boat with a 1236 description is 12 feet long and 36 inches wide.

Why Is It Important to Know the Length of Your Boat?

A male using measure tape while building a canoe in his workshop.

Knowing the correct measurements of a boat is important for several reasons.

  • To buy the appropriate insurance for the boat, you will need the correct measurements.
  • Safety equipment laws that govern boats vary based on the boat’s LOA – Length Overall.

“LOA stands for “length overall” and measures your vessel’s length, including any spars that protrude from the hull or platforms on the stern.”

  • The boat length is required to buy a boat cover that fits correctly. A boat cover that is too large can collect water, and a boat cover that is too small may pop off from the tension created by a blast of wind.
  • When determining the chain length of the boat’s anchor, its measurements are incredibly important.
  • Most docking fees and storage costs are based on the boat’s length, with larger boats requiring increased docking fees.
  • The boat’s length and beam measurements dictate the size requirement for a trailer to pull a boat safely.
  • The costs of boat transportation are dependent on the boat’s length. Transportation logistics are essential because certain boats are not allowed to be transported on specific roads. Laws may limit the time of day a certain type of boat may travel.
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“How far you need to transport your boat is only one part of the equation. Another critical factor in determining the price is the size of your ship.”

And, if you ever wanted to sell the boat, a potential buyer will certainly want/expect you to have this important information readily available. It is hard to sell a boat without true dimensions.

How Should Swim Platforms be Handled When Measuring a Boat?

A White yachts on an anchor.

Swim platforms are generally a few feet wide.  An integrated platform on the boat built for swimming should be included when measuring the length of the boat. For simplicity’s sake, while measuring, why not take two measurements? One with the swim platform and one without.

How Should Deck Extensions or Outboard Motors be Handled When Measuring a Boat?

Your boat may feature an outboard motor with support brackets or other types of attachments and handles. These features should not be included when measuring the boat’s overall length, except these factors may become relevant if you have plans to transport your boat.

Pro-Tip – Check with the carrier before assuming you know how the transportation costs are measured. A mistake could cost a lot of money.

Measuring Pontoon Boats, Sailboats, or Boats with Outboard Motors

The measurements for sailboats, pontoon boats, and water vessels with outboard motors may not impact the application of relevant laws, but they are essential with regard to transportation issues.

Measuring a boat can be tricky if you don’t know what you are doing. With simple instructions, a bit of tenacity, and online guidance, measuring a boat accurately is quite possible.