How to Measure a Boat

The proper method for measuring a boat is not as straightforward as it might seem. It actually involves several different measurements.

Why do I need to measure my boat?

Measuring your boat properly is important because this information is used to determine your boat's registration costs, what accessories to purchase or how much ventilation your boat needs. Boat measurements are also important when determining the dockage, storage and transportation needs of your boat.

Your new boat will come with an owner's manual that includes manufacturer's specifications that indicate your boat's measurements; however, these measurements do not always correspond exactly to measurements you would find if you measured the boat yourself. If you have any issues with registration or with docking your boat, you'll want to take new measurements to be sure they are accurate. You might also need to take measurements if you built your boat yourself or if you bought the boat secondhand and do not have the manufacturer's specifications.

For an accurate measurement, use a measuring tape that does not stretch.

Different boat measurements

There are three main measurements for any given boat. These are the overall length, the overall height and the beam. You might also need to measure the load waterline, which indicates how low your boat sits in the water when it is fully loaded. This measurement can determine if your boat is overloaded or not.

The above measurements are determined as follows:

  • Overall length (also known as length overall or LOA). This is measured along the boat's centerline from aft to forward, on the outside of the hull. If your boat has an attached outboard motor, a swimming platform or a bowsprit, this is not included in the measurement.
  • Overall height. To determine the overall height, measure from the keel's bottom to the highest point on the boat. This includes any additional pieces that cannot be removed. This measurement is also important for transportation. If your boat is taller than standard clearance under bridges-usually just under 14 feet in the United States-you must determine how to either avoid overpasses or make your boat slightly shorter for safe transportation.
  • Beam width. The beam width indicates the width of your boat at its widest point. This is important for determining the size of a storage facility, boat slip or dock, or transport trailer. It can also determine whether you need a special wide-load permit to transport your boat on the highway; this is sometimes required for wide-beam boats, generally larger than 8-1/2 feet wide.
  • Load waterline (also known as length of waterline or LWL). This measures the boat parallel to the centerline, from the back to the point where the water meets the front. Because of the way the boat is shaped, this measurement will be longer the deeper the boat sits in the water.
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