Is a supersonic boat possible?

Well, a submerged "boat" WOULD certainly be able to reach supersonic speeds.

 

To have a hydrofoil in the water while the boat is going supersonic would put such horrendously huge loads on the foil and struts that they would collapse. Even titanium could not possibly hold up. Remember that the water brake on current jet hydrofoils is usually a 3x5cm steel pin on a big hydraulic ram- anything more would be snapped off by the 300mph water. A hydrofoil strut would either have to be so huge as to cause horrendous drag, or would snap off under the pressure. Recall water is about 600 times denser than air and thus exerts about 600 times as much force on a given structure.... and the wings of supersonic jets are already under horrendous stress.

 

Boats

A boat is something that MUST operate on the surface of the water because it's NOT an airplane.

Simply because a vehicle has a jet (or rocket) engine doesn't make it an airplane.

Ask any Florida cracker who has an airboat.

 

Stability

Important question with no easy answer.

 

Strength

http://www.users.myisp.co.uk/~climengs/bluebird/coniston.htm

Take a look at everything that was STILL ON Donald Campbell's Bluebird.

 

Why try a hydrofoil? Let's skip straight to submarines!

 

Boats

http://www.deepangel.com/html/the_squall.html

Because that's been done, they're just not that interesting a challenge.

 

There are some basic advantages to boating over flying:

1. Load capacity
2. Start and stop any time / any port
3. Fuel economy

It seems that by the time you go supersonic you have lost 2 1/2 of them. Remember the Concorde? When the novelty died and now that working people (executives) have laptops and in-the-air telephones it is no loger a good use of resources and must be heavily subsidized.

 

Asother gets the dirty sock trophy...

Hello...

The dirty sock trophy goes to the 'person' who realizes the folly in technology and it's obvious current replacement...

Slam a few sattelites into orbit and give your high paid executives a laptop and take away their expense accounts and what do you have...

Public dividends...

That and a bunch of flat assed typist nerd heads with a Fortune 500 subscription and a brief case filled with peanut butter sandwiches and a black umbrella...

I prefer the old 1970's vision of the world dashing CEO with a great idea that gets lost in the onboard complimentary drink bar, and sometimes literally in the Swiss flight attendant...

Where was I...

Oh yes - all of the above - plus - how do I mix my cocktail, and then set it down where it won't spill onto my silk socks - while I get my ship out of the way of the semi submerged Taiwanese container box full of toasters that is floating just ahead of me - me, going 800 mph or plus - whilst telling my wife, below, to hold onto the toilet grab bars, and the crew same, so we can all tack at more than subsonic speeds - ALL AT THE SAME TIME - hehehe....

SH.

 

Bluebird K7.
As I understand, the boat began skipping on its sponsons, then became airborne after the pilot applied the waterbrake and cut thrust. Upon hitting the water again, everything forward of the compressor fan was torn to shreds. The stern survived the impact because the front fifteen feet of boat had already absorbed most of the craft's kinetic energy by collapsing.

Bluebird was doing 320mph when she crashed. To go supersonic would require double that velocity; hence, the loads put on such a craft by wind and water would be four times what Bluebird had to handle.

Operating envelope tolerances would likely be tighter than a human pilot could manage. Think flying an F-18 on afterburner in severe turbulence at an altitude of six inches, and you'll have an idea how difficult a task it would be. The slightest ripple would require the exact and instantaneous adjustment of every control surface on the craft within milliseconds. Try driving a Corvette with the electromagnetic suspension- it updates each of four suspension units 1000 times per second. Now think how that ride would feel at ten times the speed, with each bump transferring a hundred times as much force to the vehicle. Computer controls faster than those of a modern fighter jet would be needed to keep this thing stable. It can be done, yes. But it will not be easy, cheap, or safe.

 

Alternatives

How many times do I have to mention hydrofoils and supercavitation configurations before people stop thinking planing hulls are the only approach?

 

Planing hulls are certainly NOT the only approach.

 

What is the waterline length for a displacement hull capable of supersonic speeds?

 

Very, very very long with huge amount of horsepower per ton, something like 50 hp ton or more? I don't know exactly, but just a lot of HP per ton.

 

Very true. Very true indeed.

A note on supercavitation. The fastest current water-borne craft of any sort are supercavitating rocket-powered torpedoes. Problem: Here we are talking about supersonic. For a surface craft to go supersonic requires that it achieve 344 m/s or 1238 km/h (at sea level, 20 degrees Celsius). At this speed it is going supersonic in air. A submerged craft, like a supercavitating torpedo, must achieve 1531 m/s or 5512 km/h to exceed the speed of sound in sea water. Example: A torpedo going 1500 km/h, which would be Mach 1.2 in air, is only going Mach 0.27 in water. Sonic velocity is dependent on the medium and to be truthful in our claims we must measure it in the medium in which the vehicle is actually travelling.

(Note that to for a submerged torpedo to go supersonic would require it to reach what an aircraft pilot would consider Mach 4.4. At this speed, frictional heating at 80,000 feet altitude is sufficient to melt high-grade steel. I don't dare to imagine how much stress a vehicle at this speed would be under if it were touching water.)