Cavitation is actually water boiling???
In the second of our series on new technologies and other cool things) we continue with another article from Rockwool (the sponsor of the Danish SailGP F50 catamaran).
By Steven Pisano - https://www.flickr.com/photos/stevenpisano/48116076138/, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=81485849
The new class of racing yachts are catamarans that are designed to fly through the air on hydrofoils rather than sail through the water on their hull's. Reaching speeds of 100 kph these bad boys are not so much as pushing through the water but sailing over it. The materials that these boats 'fly' on have to be light, strong and perfectly tuned. Similar to F1 car racing and jet fighters the science behind sailing has reached into the future.
Although the materials are cutting age the reality of old school physics must be observed and delt with. Today a F50 can rise out of the water on hydrofoils that are 8 feet long made of high modulous carbon fiber and titanium. Thats where the old school physics come in as although the boat is flying faster, this speed is at the expense of cavitation. And cavitation at 100 kph can be a disaster.
Now for the older crowd, cavitation was how the US discovered the Russian submarine in the movie Hunt for Red October (one of my favorite non-James Bond roles for Sean Connery). And many have firsthand seen cavitation when sitting on the back of a ski boat. In short...Bubbles. For the Red October those bubbles could be picked up on sonar and in your ski boat they blend into the trail of white behind your boat. Cavitation is a well-known concept for designers of anything with fast moving water blades – like propellers or hydrofoils – and describes the formation of air bubbles or cavities in water when it passes over such an appendage at high speed.
In these situations, the difference in pressure can be so significant from one side of the blade to the other, that the water begins to boil, yes BOIL, forming a pocket of air that dramatically affects its hydrodynamic efficiency. When your ski boat propeller causes cavitation it's at the expense of momentum but in a sailboat it's at the expense of control. (You can't turn a boat that doesn't have connection to the water...)
So if this is interesting to you, read the link and thanks again to Rockwool for an informative piece that discusses some new technologies in their battle with the rules of physics.
How ‘cavitation’ and ‘dirty air’ affects the performance of SailGP’s F50 catamarans (rockwool.com)
(of note...the boat driver is still called a 'Helmsman' but there is a new role...the 'Flight Controller'. He is responsible for the wings that hold the boat above the water.)
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