Some nautical terms need to be mentioned, this blog is for everybody, not only for specialists.
LOA means Length Over All, and is the longest length of the yacht.
LWL is the Length of the Water Line.
Hull is the shell and framework of the floating part of the boat.
As a tip, you can know what could be the approximate speed of a boat, just knowing the LWL. This is called Hull Speed, sometimes displacement speed, and is the square root of LWL in feet, multiplied with a constant, calculated to be 1,34.
“v” is measured in Knots (kn), which defines another important nautical term. So, 1 kn is a speed unit representing 1 nautical mile per hour (mph)
1 nautical mile is 1.852 km/h or 0.514 m/s and approximately 1.151 mph.
In the modern naval architecture, the hull speed is too “yesterday”, more important is considered the Froude Number, or the speed/length ratio, given by this formula:
where “V” is the velocity (speed) in kn, and LWL is the length at the waterline. Actually, the Froude Number is
where “g” is the gravitational acceleration (this is also a constant, 9.8 m/s²) and “L” is actually the waterline length.
I considered this a tip because when you ask for the maximum speed of the boat, you can check the answer by calculating quickly and discretely the hull speed. If the difference is less than a knot, than the owner is a good guy. This may be especially available when you buy in Turkey, I’ve seen people lying about the speed and about a lot of other things, another one being the qualifications they have.
Originally, speed was measured by paying out a line from the stern of a moving boat. The line had a knot every 47 feet 3 inches (14.40 m), and the number of knots passed out in 30 seconds gave the speed through the water in nautical miles per hour. This method gives a value for the knot of 20.25 in/s, or 1.85166 km/h. The difference from the modern definition is less than 0.02%.
Of course, when you buy such a yacht (this is a Ferretti 800), you don’t need the discreet check I was telling you about, :). I hope you’ll learn something today :). I think I should continue with some more terms, in my next posts.
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