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Tourmaline
2nd December 2009, 08:11 PM
Clear explanation and graphical analysis of the dynamics involved in hydrofoil boats.

"But there's another way to go fast on water. It's been around for a while, but it's coming into its own. Make it fly! In September 2009 the sailing hydrofoil l'Hydroptère broke the world speed sailing record (subject to ratification) with an average speed of 51.36 knots over 500 meters, and hitting a peak speed of 55.7 knots. But underneath this amazing scientific and technological feat lies a mathematical catastrophe.
So what are hydrofoils?
In essence, hydrofoils are wings designed to work in water. As with aeroplane wings, a combination of deflecting the water and altering the speed - hence the pressure - provides a lifting force, raising the boat from the water. The foils themselves create drag, but at speed, there is less drag from the foils than from the hull.
The exact balance of these differing effects is intriguing. So let's have a closer look at it."


Analysis and graphs at:


http://www.penzba.co.uk/Catastrophe/

berntsen
2nd December 2009, 10:55 PM
Very well written article, thanks!

/\/ikolaj

ka8uet
2nd December 2009, 11:19 PM
However, I'd be curious as to how one could stay up on hydrofoils in bad weather. If one's only intent is to go fast on smooth seas, (relatively speaking), then this would seem to work well. However, if one intends to actually CRUISE in the boat, I'm not so sure it would work!

BigCat
4th December 2009, 10:11 PM
However, I'd be curious as to how one could stay up on hydrofoils in bad weather. If one's only intent is to go fast on smooth seas, (relatively speaking), then this would seem to work well. However, if one intends to actually CRUISE in the boat, I'm not so sure it would work!

I don't think I'd want to be up on hydrofoils in bad weather - but I'm pretty sure that your typical cruising catamaran is much to heavy to benefit from hydrofoils.

ka8uet
6th December 2009, 01:35 AM
I'm sure it is, too! However, I wondered what would happen to a racer caught out in a storm during a race, or is this simply a technique for speed records?

BigCat
6th December 2009, 01:51 AM
I'm sure it is, too! However, I wondered what would happen to a racer caught out in a storm during a race, or is this simply a technique for speed records?

I've never heard of hydrofoils being used during an offshore race. Maybe in a day race, but I'm not sure. Usually they are on experimental / speed trial sailboats, and power vessels such as fast ferries.

solarbri
9th December 2009, 08:13 AM
Aren't curved daggerboards in the outriggers of a trimaran essentially acting as lifting foils?

...kind of, sort of???

Couldn't they (or something similar) somehow make a 30,000lb cruising cat feel like a 15 or 20,000lb cat? Not flying, but ...floating...HIGHER?:D

3Psuite
9th December 2009, 07:48 PM
Foiling in real seas

http://www.youtube.com/watch?v=r4xGys7iL-4
shorter version with music
http://http://www.youtube.com/watch?v=wMM0_P5CtFQ (http://http//www.youtube.com/watch?v=wMM0_P5CtFQ)
Long version

enjoy

multihullsailor6
9th December 2009, 08:23 PM
Not quite on the topic, but how about a foiling Optimist?
http://foilingboatadventures.blogspot.com/2009/12/foiling-oppie.html