Steam jet boats

[A_Appleyard]

What designs are there for a solid-fuel-fired or oil-fired steam jet boat? Full size, from cabin cruiser size up to patrol boat size, not toy. I.e. it propels itself by blowing a jet of high-pressure steam backwards without cylinders or turbine and propeller or impeller. I heard of a real steam-jet-powered lifeboat, but I have no reference to it.

[D'ARTOIS]

It is the same level question as "are supersonic boats possible?"

I used as a kid to play with a few, when batteries were almost impossible to get and we could enjouy ourselves a longtime with these small "pof-pof" boats, fuelled by a waxine light.

My question - what's the use? All steam engines are very hungry animals; you need water and fuel. The uncompressed steam, or hot air, powers the boat at a non efficient rating if you calculate the mass of fuel it requires.

Nontheless an inventive question.

[A_Appleyard]

I don't mean a "pop-pop boat". I have heard of those toy steam pulsejets. I mean: a boiler like in an ordinary steam engine, but blowing its high-pressure steam straight out back in a jet.

[cyclops]

The only known effecient way to use Steam is thru a steam turbine engine with gears and a lot of heavy additional supporting equipment.

[Bern]

Good job, Appleyard, think outside “The Box”. I believe it does us all some good to stretch our gray matter a little. ---- Run the numbers. What can it harm, you will learn something that will help fuel curiosity, and that is good!!! --- I have heard that when some of the first ideas of jet engines where thought about, questions came up like, “What, you expect to push something big and heavy by just blowing some hot air out behind you?” Just don’t tell the manufacturers of today’s aircraft jet engines that.

[artemis]

Yeah, Bern - indeed let's think outside the box!
This has been around for quite awhile in the hobby steamboat fraternity. Using the concept of the steam injector (high velocity steam moving through a venturi "nozzle" and propelling water into a boiler) with a direct conection to the water the boat is in and "shooting" the combination out under water and in the desired direction of travel ("swivel propeller pod"). Not much has been done with it due to the inability to recover/condense the steam - and therefore require a larger tankage of boiler water aboard. But, if you're on a clean freshwater stream or lake, it might work with a high pressure, monotube boiler.

[marshmat]

Look up a company called Pursuit Dynamics: http://www.pursuitdynamics.com/marine.php
Their PDX technology is perhaps the most promising steam-based jet system currently being studied. Instead of just blowing steam out the back (which is not efficient at all), the PDX injects steam into a water flow and relies on the shock wave produced by the sudden condensation of the steam to accelerate the water in the tube. It's a mathematically nasty, but extremely effective and efficient way of using steam as a jet drive. They claim fairly high efficiencies at pressures as low as 4.5 bar, and some of their stationary pump versions run at 30+ bar steam pressure. (A 30hp marine drive unit, they say, would be about a foot long.)

[A_Appleyard]

Originally Posted by artemis

... Not much has been done with it due to the inability to recover/condense the steam - and therefore require a larger tankage of boiler water aboard. But, if you're on a clean freshwater stream or lake, ...

Most steam railway engines used to carry a big tank of water and throw used steam away instead of condensing it :: that it why railway engines used to go "ch ch ch ch" much more than steam-powered ships. They used to scoop up water from a "water-trough" between the tracks as they went. That made the tracks wet, which in my experience caused miaow-type noises from the train's wheels.

Back to topic. At sea the problem is salt. How efficient likely would be continually bleeding the boiled-down water from the boiler and injectoring new water in to stop the water in the boiler from getting concentrated enough for the salt to crystallize out? The bled-off hot water and the intake cold water could go through a countercurrent heat exchanger to conserve boiler heat.

Also: please where are diagrams of a ship or patrol boat sized solid-fuel-type steam boiler, in enough detail for me to make a CGI (= computer-generated image) model of it. including its stoke-hatch and the inside of its furnace etc?

[A_Appleyard]

I searched for "PDX Marine Drive" in http://www.altavista.com, and I got these 6 results:-
- http://www.pursuitdynamics.com/marine.php ::The technical matter is on http://www.pursuitdynamics.com/pdx.php .
- www.pursuitdynamics.com/downloads/annual2002.pdf :: Business report waffle, nothing technical.
- http://www.fillyaboots.com/_fybArc1/000001da.htm :: Business report waffle, nothing technical.
- http://ig.insightgrit.com/r/i2.asp?r...PDX.L&id=PDX.L :: Stock exchange blah. Absolute zero useful.
- http://www.fillyaboots.com/_fybArc1/000001de.htm :: More finance junk.
- http://www.marathonmarine.com/docs/stpb_jetboats.html :: Useful information about jet boats in general, but the part about motors seems to be all about impeller pumps.

[cyclops]

Lets get in on the bottom floor of this fantastic bussiness. Send lots of money.

[artemis]

Originally Posted by A_Appleyard

...Back to topic. At sea the problem is salt. How efficient likely would be continually bleeding the boiled-down water from the boiler and injectoring new water in to stop the water in the boiler from getting concentrated enough for the salt to crystallize out? The bled-off hot water and the intake cold water could go through a countercurrent heat exchanger to conserve boiler heat.

This technicque was used on VERY early marine boilers. Every hour the engineering officer on watch would draw off water from the boiler and float a "salinometer" in it - the higher the salinometer floated, the greater the salt and other solids contamination. At a certain point the boiler was partially blown down and filled with "fresh" sea water. With the advent of "high pressure" c. 1850s (about 50psi or 3+bar) the practice was discontinued and a condenser fitted. Economy through reuse of the condensate (at a higher temperature than sea water) was significant.

Originally Posted by A_Appleyard

...Also: please where are diagrams of a ship or patrol boat sized solid-fuel-type steam boiler, in enough detail for me to make a CGI (= computer-generated image) model of it. including its stoke-hatch and the inside of its furnace etc?

There are gazillions of books out there. The older B&W books (prior to 1928) are one place. Check the links pages of organizations such as the International Steamboat Society http://www.steamboating.org for places to look. Also check with your local library.

As to the PDX concept - this is a variant on an air movement device developed by Exair. Some hobby steamboaters use this device to provide forced draft to their pressure atomizing burners - steam is used instead of air as the medium to force air into the firebox. Exair claims a 25X volume of air moved with design. Exair's website is at http://www.exair.com/index.htm . Search for "adjustable air amplifier".

[marshmat]

Hmm... Exair's units look similar to Pursuit's, but they appear to be operating on fundamentally different principles. The Exair device (designed to transfer pressure to kinetic energy in a gaseous flow) appears to be essentially a coanda venturi- it blows a high-speed, high-pressure air layer along the walls of its chamber, thus creating a vacuum in the centre and drawing air through. As far as I know, Pursuit's technology (designed to transfer thermal energy to kinetic in a liquid flow) is based on the pressure shockwave produced by a sudden phase change, and uses the venturi shape only to bring the liquid stream in properly. As far as I can tell they are fundamentally different technologies. Anyone who knows more about either of these units, feel free to elaborate...

[A_Appleyard]

Originally Posted by cyclops

Lets get in on the bottom floor of this fantastic bussiness. Send lots of money.

Sorry about any misunderstanding. I am not starting a scheme and I am not asking for money.

[greg simpson]

sorry,coming in quite late,ut that steam-jet lifeboat you heard of was a lifeboat that had twin cylinder oscillating engine driving a turbine that,by the use of four valves for'ard s'board,for'ard port,sft starboard,aft port,the direction of the jet,and thus the direction of the boat,was changed.
built by thornycroft i think if i remember right,and there was also one built in holland.

hope that hepls a bit.

ps.have you thought about how high steam consumption would be if a boiler exhausted straight into water?
what boiler design wee you thinking of that could produce sufficient ammount of steam of sufficient pressure?
on the question of pressure,opening it up a bi,how high would you think the pressure would have to be?
surely only higher than atmospheric pressure,if used in the right exhaustive environment,would be sufficient?
or were you thinking along the lines that more steam=more speed?
perhaps you should do some experiments...

greg

[kjell]

Now is the time to use Hydrogen as a steam generator. I have had this idea to make a marine pulse thruster. The exhaust from the burned air / hydrogen mix is conducted in the middle of a multi venturi "nozzle" converting the high speed gas in to slow speed water movement. Adapting the pulse frequency to the wave frequency will maybe reduce hull frictions as fishes do.