This is also the maximum speed of the sailing vessel. Hull speed has been attained at this point. Then there comes a point where the speed pushes the wavelength to stretch out to be that of the boat’s waterline length and the bow and stern wave merge creating one long trough that runs the length of the hull. As the boat speed increases the corresponding waves rise and troughs also extend and the number of cycles between the bow and stern reduce. At lower speeds, the wavelengths between the waves are shorter so there is room for multiple cycles of waves to pass down the length of the boat before meeting the stern wave. When displacement hulls proceed they push aside significant amounts of water creating a wave train at the bow and another at the stern. ![]() The physics behind this is driven by wave cycles. For instance, if a cruising sailboat has a waterline length of 36 feet, she should be able to sail 1.34 x 6, or approximately eight knots. Hull speed can be expressed as a simple mathematical formula 1.34 X the square root of the length of the waterline (HS = 1.34 x √LWL). This refers to the horizontal length of a hull at the water’s surface when a boat is carrying a normal load and it is this length, in conjunction with the laws of natural physics, that governs the boat's hull speed. However, it is not the boat’s length overall (LOA) we are talking about here but rather the load waterline length (LWL). ![]() This is largely dependent on the waterline length of the boat and generally, the larger the boat, the faster it can go. It is this saying that all these numbers have in common.ġ/ Your Boat's Hull Speed: Find out your boat's hull speed and don't try to push beyond it.Įvery displacement boat has a mathematically defined maximum 'hull speed'. There is an old sailing expression that goes any damn fool can put up sail, it takes a sailor to know when to reef'. But there are three simple numbers that newcomers can keep in mind to keep them sailing comfortably and efficiently. All boats are different and conditions, of course, vary widely at sea.
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