Submarine driven by kites

Hi, Just brain storming...

What if you develop a submarine/torpedo driven by kites,
Fish are faster underwater, Race swimmers try to prolong their "under water start" as long as possible.

might be a speed record holder.

 

If everything hydrodynamic and power is the same, I don't think there is anything that is faster underwater than the equivalent displacement craft because total surface friction is more when under. But I may be missing something...

Porta

 

You miss the energy that causes drag by generating waves.

 

Kites advantage is being able to get higher speed air at higher altitude without the righting moment sacrifices of tall masts directly over boats. A side effect is net lift, but it comes at the price of angle of attack. At high speed angle of attack is everything -presuming two directional requirement (without which speed record is just someone swept up in a tornado). So since a kite produces net lift if the body of the craft is below water you have buoyant lift that must also be overcome, and drag of any volume is greater below water than in air. So the answer is that any volume or small mass of a kite driven craft is better above the water than below with surface piercing foils.

 

The reason you have submersibles and torpedoes is that stealth is obtained by hiding below the surface of the water. If you attached kites to such vehicles, you are, in essence, putting up a big, flashing billboard that screams, "Here I am! Come and kill me!"

It's also not clear that the drag from any cables attaching the kite to a submerged vehicle could be minimized. Cables with circular cross-section have a relatively high drag, and it would be difficult to keep more aerodynamic cables properly oriented in the water to reduce drag.

 

Isn't that what a hydrofoil is doing to some extent? You would still need the kite attached to the sub, which would pierce the surface of the water, and then also some foils below to allow the sub to track. I'm not a designer of any sort, but a sub specific thing seems really goofy when a hydrofoil does it already with the drag of the people carrier above the water where the overall drag would be less.

Again, I'm not a designer. Just come here to see what's happening, and to read the historic multihull thread, which is awesome.

 

What scales are you considering? At low speeds/large boats seems like hull speed not much of a factor? Seems like small displacement boats might go up on plane (or reduced displacement) at some point with a kite. Also seems like a kite would pull a sub up to displacement mode, unless some energy is diverted to keeping it submerged. Just my humble thoughts, FWIW....

Porta

 

I doubt the idea is feasible for many of the reasons above, it's not really too feasible for yachts or ships YET. But hydrodynamic drag could be significantly reduced using the super-cavitation technology the Russians use on their super fast torpedoes.

 

Probably not a practical idea, but there are reasons to consider the concept.

The ability to not loose energy due to surface waves is a plus, but the extra surface friction is a minus. The ability to have next to no boat motion in response to waves is a big plus.

A very small strut/arm with a good NACA 009 or so section (just thick enough to not start oscillating) up from the boat to the surface will probably be lower drag than a round cross section cable. The strut also allows for an easy com cable to link to cameras above. If you want to use the strut for air to/from the boat, it needs to be bigger and drag goes up.

Down at the boat, main foils extending outward (at rest) on both sides provide the daggerboard function of a normal sailboat. The whole boat heels over a lot so that the strut out of the top (at rest) rotates 45° to 60° when sailing.

With this configuration there is no potential for main foil air entrainment, and reduced potential for cavitation. Cavitation is a function of the absolute pressure of a fluid. At 1 ft below the surface, the absolute pressure is 14.7 psia + 0.4 psi = 15.1 psia. At 10 ft below the surface, it is 14.7 psia + 4.3 = 19.0 psia.

 

Not to mention the effect it would have on trim subs are very sensitive to trim, and forgetting the drag from the cables and the issues with stealth it would make it's submarine very hard to handle...(MMC/SS)

 

Looking around, it appears to me all the fastest sail and power boats around either plane and/or run on foils.

 

Hydrofoils are rigidly attached to the hulls they support, so it is much easier to keep the surface piercing portion of the apparatus oriented to give minimum drag thru the water. With a kite driven by the vagaries of the wind, this is a much more difficult proposition.

 

Haven't heard of anyone designing a kite yet that didn't have to be actively "flown" (that's their big drawback). Hard to do from underwater.

 

A semi-submersible could be a better solution. The majority of the hull is below water, but a couple of struts are above water as attachment points. The stability problem will be harder to solve than on a conventional hull. However, if there is no problem with a considerable angle of heel, it may be acceptable.

 

yawn;;;;;the same old subs faster than surface argument. why don't the powerboat racers switch to subs.