Is there a maximum speed for a dragon boat? Has it anything to do with “hull speed”? Can we answer those questions of whether a 10 paddler boat should be faster than a 20 paddler boat?
Some clever person should be able to work out how fast a particular crew should be able to paddle. Maybe by measuring enough things (crew weight, crew power, how smooth the hull is, how deep the boat sinks into the water, the density and temperature of the water, etc. etc.)
And maybe they can, but I haven’t seen it.
What I HAVE found is this notion of “Hull speed”. This is NOT a limit on how fast the boat can go. Instead, it just indicates that to get past this speed you have to inject a hell of a lot more power.
In this post we will calculate the hull speed of a dragon boat.
What is Hull Speed?
When a dragon boat moves ahead, the water is parted to allow the hull to move through it. Thus causing a bow wave to form at the forward end of the hull (bow) and a similar one at the back (stern).
The waves produced travel at a certain speed (the speed of the boat) and have a length appropriate for that speed.
As the boat speeds up, the waves get longer. Eventually, reaching a speed where the waves created near the bow have their second crest a bit ahead of the stern. This results in the boat effectively sitting on a wave at the bow and at the stern. The longer the boat, the higher the speed at which this occurs. (this is important)
Once we go over that speed, the second crest of the bow wave is now behind the boat and the stern drops into the trough.
As you can see, for the boat to go any faster it has to go up and over the bow wave which requires much more power.
If you look at this video you will see the back end of the faster boats in the trough as they exceed hull speed. (This post’s featured image is also a good example)
How do we calculate hull speed?
William Froude (1810 to 1869), a British engineer who had a special fascination with the sea and ships carried out some experiments. He determined that there was a relationship between hull speed and waterline length (LWL).
Hull speed (in knots) = 1.34 x the square root of the waterline length (in feet)
Hull Speed (in m/sec) = 1.25 x the square root of the waterline length (in metres)
What is the Hull Speed of a Dragon Boat?
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