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Precise boat waterline length calculation

Oct 07, 2020

less than a min

  • Precise boat waterline length calculation

    Being new in the world of boats can seem daunting and scary. There are a lot of words, terms, and even calculations you need to be aware of in order to know what is going on with your boat. Whether you are a boat owner, crew member, or even just a guest on board, there is no harm in being a bit more informed on the basic terminology. In this article, we will show you what a waterline length calculation looks like and why it is important.

    Let start from the beginning.

    What is the waterline length calculation used for

    The waterline length calculation is based on the waterline length or also known as just L.W.L. It is the length of the boat on the line where it sits on the water. Generally, the waterline length of the boat is shorter than the overall length of the boat. This happens as a result of stern and bow protrusions. For multihulls, the waterline length is measured from the tip of the stern to the end of the bow on the hull.

    The waterline length is measured with the boat default load condition. This is an important detail to keep in mind as the waterline length will vary depending on how heavy the boat is. The heavier the boat, the deeper if sinks into the water, and the bigger the waterline length is. However, in order for the calculation to be an objective measurement, the L.W.L. is registered with a default load in the boat. The waterline length calculation is used to determine how much water the boat will displace, how fast the hull is, how much paint the bottom of the boat needs as well as where the stern and bow waves happen.

    Waterline length calculation

    The waterline length calculation is used to determine how fast a boat can go. A longer waterline length means a greater speed for a sailing boat as it increases the sail area without needing a bigger beam or draft. A bigger beam causes higher hull drag which requires more power to accelerate. Therefore, the waterline length is used in the calculation of hull speed as below:

    Hull speed = 1.34 X Square root of LWL

    The maximum hull speed is measured in knots. This is the speed where the wavelength of the bow wave reaches the waterline length. Such a calculation is important because this speed allows the boat to drop into a hollow between two waves. This is a situation in which large sailboats get stuck, while smaller and lighter boats can easily overcome.

    The length of the waterline has been used as the main measurement in racing sailboats which in turn pushed designers to include longer overhangs fore and aft into their boats. What then happened is that the initial waterline length of the boat was shorter, but it became longer as the boat heeled over. As a result, a greater speed was reached.

    You can learn more about the waterline length calculation and other important equations such as displacement to length ratio at TheBoatDB. Follow our other articles in the blog or explore the app for free in more detail to get more acquainted with marine terminology. At TheBoatDB you will have all your boating life in one app and save yourself a great deal of time and energy when it comes to maintaining your boat properly.

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