Is a supersonic boat possible?

[Franklin]

http://www.hydrofoil.com/whyhydrofoil.htm

http://www.hydrofoil.com/reference.htm

http://www.hydrofoil.com/gallery.htm

[Sketch]

How low can you safely fly a plane?

The speed of sound at sea level is 340.29 m/s. That is about eight times faster than the fastest hydrofoil. Supersonic flight is an engineering marvel, a topic on which other members can speak much more knowledgeably than me. Considering that that water is 784 times more dense than air, why would you want to dip an appendage into such a medium if the goal is speed? For stability perhaps? Look what happens when you go to the rolling heap for stability at 60 mph (see above websites).

Is it possible? I am always the optimist, but why? The forces acting on such an appendage(s) at supersonic speed would be huge, with resultant drag penalties. Of course there is also cavitation to consider. I'm curious, what happens if any solid is moved through water at supersonic speed? How long will it take to dissolve ?

[RANCHI OTTO]

Yes...but only if God will permit it.....!

Ranchi Otto

[markdrela]

Is a supersonic boat possible?

To allow a meaningful answer, you will first have to define what constitutes a "boat". How about if I take an F-15, and fly very low while dangling a piece of wire in the water? Is that a boat?

This is not a silly question. This very issue came up when Doug Milliken was commissioned to write the rules for the DuPont Human-Powered Watercraft Speed Prize, in the late 1980's. It was pretty clear that the fastest way to traverse the speed course would be in a human-powered airplane. To rule this out, he considered all sorts of "boat" definitions. Merely requiring contact with the water was not sufficient, because of the airplane with trailing wire solution. In the end he decided that the boat had to derive a majority of its lift and control forces from the water. Propulsion was left unspecified.

This definition worked well for a human-powered boat, but it probably wouldn't be an enforcable for an extremely fast boat. Saying "no air lift" would probably disqualify most current hydroplane boats. How can you prove that air isn't providing a significant amount of lift to the vehicle? Ditto with air fins providing stability and control.

[Franklin]

Originally Posted by markdrela

To allow a meaningful answer, you will first have to define what constitutes a "boat". How about if I take an F-15, and fly very low while dangling a piece of wire in the water? Is that a boat?

This is not a silly question. This very issue came up when Doug Milliken was commissioned to write the rules for the DuPont Human-Powered Watercraft Speed Prize, in the late 1980's. It was pretty clear that the fastest way to traverse the speed course would be in a human-powered airplane. To rule this out, he considered all sorts of "boat" definitions. Merely requiring contact with the water was not sufficient, because of the airplane with trailing wire solution. In the end he decided that the boat had to derive a majority of its lift and control forces from the water. Propulsion was left unspecified.

This definition worked well for a human-powered boat, but it probably wouldn't be an enforcable for an extremely fast boat. Saying "no air lift" would probably disqualify most current hydroplane boats. How can you prove that air isn't providing a significant amount of lift to the vehicle? Ditto with air fins providing stability and control.

http://www.lesliefield.com/other_his...hydrofoils.htm

http://www.lesliefield.com/images/al...l_hd4_1919.jpg

Hydrofoil boats have been around for something close to 100 years.

Casey Baldwin (working with Alexander Graham Bell) set a World Water Speed Record of 70 mph with one in 1918.

http://www.foils.org/racers.htm

http://www.foils.org/US-3%20Hydrofoil.jpg

[Franklin]

Originally Posted by Sketch

How low can you safely fly a plane?

The speed of sound at sea level is 340.29 m/s. That is about eight times faster than the fastest hydrofoil. Supersonic flight is an engineering marvel, a topic on which other members can speak much more knowledgeably than me. Considering that that water is 784 times more dense than air, why would you want to dip an appendage into such a medium if the goal is speed? For stability perhaps? Look what happens when you go to the rolling heap for stability at 60 mph (see above websites).

Is it possible? I am always the optimist, but why? The forces acting on such an appendage(s) at supersonic speed would be huge, with resultant drag penalties. Of course there is also cavitation to consider. I'm curious, what happens if any solid is moved through water at supersonic speed? How long will it take to dissolve ?

The goal would be a World WATER Speed Record.

[BillyDoc]

The speed of sound in sea water is 1,531 meters/sec. So there's lots of "room" between current records and "supersonic."

Didn't Russia develop some very fast torpedoes? How fast are they?

[gonzo]

The problem is wave making resistance plus the compression of the sound waves the vessel would be overcoming. On the land speed record, a supersonic car went out of control because the shock wave was making holes in the track and violently shaking it.

[mackid068]

Silly question, but it is possible, perhaps a WIG (wing in ground vehicle?) http://www.4p8.com/eric.brasseur/swlbi.html (This website's writer says that it is possible to avoid shockwaves!)

[Sean Herron]

Hello...

I have a supersonic boat in my garage just now...

Come on over - and I will show it to you and my vodka still as well...

If I like you - we can get into the sauce and talk about our Martian brothers who await the day that we choose to plug ourselves back into the grid...

Sure....

SH.

[tspeer]

Originally Posted by mackid068

Silly question, but it is possible, perhaps a WIG (wing in ground vehicle?) http://www.4p8.com/eric.brasseur/swlbi.html (This website's writer says that it is possible to avoid shockwaves!)

What he's described is essentially the Buseman biplane. Unfortunately, he forgot about wave drag due to lift and only considered the effects of thickness.

The USAF Flight Dynamics Laboratory (now a division of Wright Laboratories) did some work on a supersonic parasol design in which the wing was mounted on a tall strut from the fuselage and wraped down and back in a continuous curve toward the tips. It was designed to intercept the bow shock from the fuselage.

Wave riders are another type of design that use these effects. The original waverider concept had a cross section like an inverted chevron and wedge-shaped buttlines. It traps a shock wave underneath between its highly swept leading edges. The top surface was designed to allow the flow to go straight past. The simplest way to design a waverider is to compute the theoretical flowfield for a virtual wedge or axisymmetric shape, and then trace out the streamlines for the flow that intercepts a portion of the resulting shock wave. Hypersonic vehicles like the X-43 also use a similar concept, with the whole underside of the forebody forming the compression ramp for the inlet and the underside of the aft fuselage being the exhaust nozzle.

The XB-70 had outer wing panels that drooped down for high speed flight to turn it into a waverider-like configuration. They called the effect "compression lift".

I think the most likely design for a supersonic watercraft would be something like a waverider with very narrow sidewalls in contact with the water. The acceleration from any kind of waves would be very high if it had much waterplane area at all. To have stable pitch-heave coupling, the waterplane area would have to be ahead of the center of gravity and the aft end would be supported aerodynamically. The problem isn't providing enough lift, of course, it's avoiding having too much. It may be designed to actually provide a steady down-force to maintain contact with the water under the expected dynamic variations.

[mackid068]

I had absolutely no idea, I just posted some website that I didn't even read But anyway, let's just say that, for now, it's impossible. Perfect conditions with a flat bottom boat powered by a few jet engines, maybe.

[Sketch]

Originally Posted by BillyDoc

The speed of sound in sea water is 1,531 meters/sec. So there's lots of "room" between current records and "supersonic."

The speed of sound in air at sea level is 340.29 m/s or 761 mph. I thought this would be a more appropriate measure for a supersonic boat as most of it will be above water - a supersonic submarine is a whole 'nother can of worms (1531 m/s is over 3000 mph!)

And yes, I was thinking of a water speed record - "How low can you safely fly a plane" was a facetious remark. I'll use more smilies next time

Kevin Barry

[mackid068]

An unmanned submarine is possible, a high-output nuclear reactor powering a vessel using jet drive, no radiation shielding or weapons, just a computer, reactor and drive.

[gonzo]

However, a submarine is not a boat so it doesn't qualify.