boat propulsion - miniature computer-controlled steam plant?

Hello all

I must leave this alone - but here's a thought which jumped to me.

Started on path of learning "embedded electronic devices". Typically boards about 50mm square with inputs, outputs and a microprocessor - as would be used to control eg. a washing-machine.

The thought must occur to an "on the spectrum" mind - for a boat - eg. auxiliary power for a sailing yacht... because you have the sea as a "cold-well temperature" to condense the working fluid steam back to water to go back through the cycle:

an embedded electronic control device would make possible a "flash-steam" turbine power unit.

It could sense temperature at the output of the "helix of tube" boiler with a thermocouple, the power draw on the machine, and instruct electric pumps for liquid fuel and the water from the condenser.

(carnot-cycle-eff (my-tc2k 800) ;; 1073.15 (my-tc2k 70) ;; 343.15 ) ;; 0.6802404137352653

The potential efficiency of the device is around 68%.

You would have fuel-flexibility - "diesel", heating oil, etc.

The drive would have to be electric (?), seeing as the turbine would spin at 10's / 100's of thousands of revs-per-minute.

The thing would hopefully be nearly silent, vibration-free and small. You'll be knowing - on a sailing yacht if you have to go over to "auxiliary power" (the wind is low or you want a heading in the "no go zone" in the

90degree included angle about the bow 45deg Port to 45deg Starboard) the sound and rumble of a diesel engine in the confined small boat is "sub-optimal".

In general steam turbine ships have smaller machinery, can be lighter-built because there isn't the vibration of a "pounding" diesel

- but up until now have a fuel-consumption penalty compared to a marine long-stroke diesel (which exceeds 50% efficiency) Thinking eg. container-ships going around the world at 25knots.

I am taking it that with stainless steel boiler tube and no consequence if it "lets go" - you put the "boiler" in a steel tube and if it "lets go" the tiny amount of steam in a flash-boiler "shoots" over the stern - probably at the water. So worked on the idea of 800C at the boiler output.

To start the thing you'd crank a manual handle which blows air and pumps water and fuel-oil in reasonble ratio until the steam-turbine spins and generates electricity the auxiliaries can start drawing-on under computer-control.

It is a nice thought that if you want to voyage when the wind isn't blowing that voyage is as silent as sailing.

A "motor-boat" with such device is a nice thought, and an easier start as a test rig.

Any comments?

This must be obvious. Has been done already?

I must absolutely leave this alone - but I had to ask if this is already known.

Rich Smith

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You could start with a low cost Tesla turbine from eBay, it uses friction within a stack of simple disks instead of expensive bladed rotors. Sensing temperature and pressure is cheap and easy, flow or more critically its absence not so much. This is definitely a lathe and milling machine project, and you want a developmental model that won't explode if there is a bug in your code, writing a stable "servo loop" isn't trivial. I struggled to step a drum plotter print head quickly without overshoot, ie open loop critical damping. will be a delay between commanding a change like opening the throttle and seeing its effect, if you just wait for it the change may become greater than intended. Many modelers use compressed air in place of steam for safety and convenience. A dangerous leak of steam at high temperature and pressure is invisible.

US experimenting with jet engines began with Nathan Price's work on steam engines for aircraft at the Doble Steam Motors company.

creating the functional steam airplane engine he dropped the steam stage and fed the supercharged combustion gas into a turbine. His struggle for high efficiency before suitable high temperature alloys had been developed slowed his work enough that the USA decided to pursue Whittle's less sophisticated but easier to produce design instead.

Tesla turbine - thanks - couldn't visulise any way with turbine

A microprocessor is probably overkill for a boat - you would run it mostly at a set speed, when you would want to know hot temperature and pressure, and engine speed, but that's about all.

If you are driving a generator then you won't be changing engine speed much either.

Though nowadays you might as well chuck a microprocessor in and see - that way lies better instrumentation, process control and outputs like efficiency, noise, engine wear and so on.

For a car now, a microprocessor gets more interesting and dynamic, especially in direct drive. I designed a flash steam car about 30 years ago, but it never got built. Hmmm...

If it's steam, basically anything which will condense the steam is enough. Though a copious cold end always helps, at least a little.

No, first a steam engine is not a Carnot cycle engine, it is a (hopefully condensing) Rankine cycle. Second, small - and by small I mean anything smaller than huge - turbines are inherently less efficient than reciprocating engines. You'll be lucky to get 15% even with really good design.

You might want to look at Sterling engines.

Steam turbine ships? see Turbinia.

Peter Fairbrother

Steam turbine ships? see Turbinia.

Peter Fairbrother

------------------------------------- In the early 60's Popular Mechanics magazine published hobbyist plans for a steam turbine powered model of the first commercial nuclear ship, NS Savannah. The turbine disk was to be machined on a milling machine with a rotary indexer using a more precise version of hole saws to cut the blade curves.

This photo from lathes.co.uk shows a milling machine like mine with the work mounted on a rotary indexer to precisely space the holes:

Tesla turbine - thanks - couldn't visulise any way with turbine

------------------------- You machine each blade with two hole saw cuts like this into the rim of the disk: (( with a smaller radius on the back one so the blade has a crescent moon profile and sharp edges. Moving the spindle to the side of the disk axis rotates the blades. The operation is similar to cutting a gear, tedious and exacting but not that difficult, and it uses standard milling accessories.

The accessory that positions the disk may also be a dividing head or rotary table. I used mine to cut a new steering sector gear for my old tractor and to groove a shaft to nearly the full depth of a motorcycle drive sprocket's splines so it could be pressed on, for my sawmill that runs the bandsaw blade on ex- motorcycle wheels.

Machining can be a challenging exercise in problem solving. The complex shapes on 1800's US military firearms were cut on very simple production machinery set up by very clever toolmakers.

Military contracts were the first combination of a guaranteed market with advance funding for new production machinery. Civilian gunsmithing retained the old methods.

The Windsor factory is a museum with some of the original Enfield machinery, still looking very impressively well made after 100 years of service.

No, first a steam engine is not a Carnot cycle engine, it is a (hopefully condensing) Rankine cycle. Second, small - and by small I mean anything smaller than huge - turbines are inherently less efficient than reciprocating engines. You'll be lucky to get 15% even with really good design.

You might want to look at Sterling engines. Peter Fairbrother

----------------------------- For aircraft the break-even point between recips and jets is considered to be around 300HP, though there are smaller jet engines down to model size.

375 MPH one HP equals one pound of thrust.

Unless you build at the low end of buy new and bolt together industrial size there will be lots of custom machining involved. Using surplus equipment may also require machining to make the parts connect together. I found that cheap and useful things were often available because they had unusual mounting or shaft coupling etc.

On the sawmill I paid as much for a new extension shaft, jaw couplers, supporting bearings and a pulley as for the new 6.5 HP gas (petrol) engine. The point was to have all the exposed moving parts on the tooth side and the engine and its controls on the guarded back side in easy reach.

Thanks for the wise words about turbines. I have heard about low efficiency in small sizes. That reciptocating engines can be used in like solar power plants where the solar energy is passed on as steam in the design. Preserved but still in viable service (?)

"Unaflow" engines. High boiler pressure for reciprocating engine at 470psi (/ 470 14.7) ;; 31.97278911564626 about 32Bar.

Thanks everyone.

Thanks for the wise words about turbines. I have heard about low efficiency in small sizes. That reciptocating engines can be used in like solar power plants where the solar energy is passed on as steam in the design. Preserved but still in viable service (?)

"Unaflow" engines. High boiler pressure for reciprocating engine at 470psi (/ 470 14.7) ;; 31.97278911564626 about 32Bar.

Thanks everyone.

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During WW2 we had two coal fired sidewheeler aircraft carriers on the Great Lakes.

I tried that, but couldn't get it to work with a suitable geometry (for an impulse turbine) - I had problems with the back edge of the holesaw hitting the workpiece. If the saw was small diameter it would intersect the workpiece on both edges, and if the diameter was large enough that it didn't interfere the turbine blade was too straight.

Had visions of a flexible belt blade running over a curved surface, but that didn't work either. Though I am thinking of reviving the idea with a sanding belt for final polishing.

Nowadays I'd use a straight milling cutter on a CNC milling machine, or do a lost-PLA casting of a 3D print.

But my turbines are small, usually less than 50mm diameter. For a yacht you'd want something bigger.

But but ... does the electrical efficiency matter all that much for a yacht? If you are using CHP (combined heat and power) the otherwise lost heat can be counted as useful output, giving 95%+ overall efficiency.

Also, suppose you had 10% electrical efficiency from something burning oil or a similar taxed fuel. You could claim back the transportation tax on 90 % of your fuel, as you would be using most of the energy from it for non-transportation purposes.

Or possibly 97.5%, as you might be using the fuel solely for cooking or heating half the time, and using half the electricity on a microwave or summat.

(on boats fuel used for transportation is taxed at a much higher rate than fuel used for domestic heating or cooking. Or it used to be, it's decades since I lived aboard)

Peter Fairbrother

I tried that, but couldn't get it to work with a suitable geometry (for an impulse turbine) - I had problems with the back edge of the holesaw hitting the workpiece. If the saw was small diameter it would intersect the workpiece on both edges, and if the diameter was large enough that it didn't interfere the turbine blade was too straight.

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I can visualize what you mean, interference limits the blade depth. The blades could be cut deeper with a small end mill if the rotary index holding the disk blank was in a swivel vise (or rotary table) manually turned only far enough to make the cut. The setup might be easier if the disk blank was fixed to a drilled index plate that took up less space, mounted on a vertical surface of a block that centered (or offset) the blank over the vise swivel axis.

I design things like this graphically by drawing the separate shapes in CAD and moving them to touch, for example the front and back circles intersecting at the blank edges, then recording the center coordinates. Trigonometry can refine the precision without much risk of gross error.

I would rough out the gaps first, milling an arc with hand feed pressure doesn't allow much depth of cut and NO climb milling.

For what it's worth - I was thinking of

• de Laval turbine

• Ljungstro..m turbine With Ljungstrom turbine, wondered if blades could be made on tips of rod pegs set into the face of the disk. The centrifugal force isn't in line to sling the inserts out of their seats. ? I wondered whether the revs would have been manageable. Two contra-rotating discs would have been fine - two generators. Presumably at those revs a couple of magnets embedded in each disk?

Idle speculation.

I got an "Arduino" embedded device working today. Advantage me seeking jobs in processing - new mines opening up around here (Cornwall).

A partial admission turbine is probably a good way, to go. Partial admission means that the incoming fluid only impinges on a few blades at a time rather than over the whole wheel.

I hadn't thought of that, it's more a bending force isn't it. And you can put rings on the other end of the blades so they are supported at both ends, with the centrifugal and pressure forces going sideways.

Though they would typically have a last ring of axial blades for best efficiency.

And possibly a pre-ring or two of impulse blades if the expansion pressure ratio is higher than about 10 (the two-spool Ljungstrom turbine is necessarily a reaction turbine, though in some ways it behaves like an impulse turbine).

Also good is that the blades are not twisted, makes them much easier to make.

Do you have to have two turning spools? [quickly googles Ljungstrom turbine, it's been a while]

Hmmm, looks like one shaft is okay, in fact there has been a lot of work on that recently (which I haven't read...yet), see eg RAT turbines for ORC.

I would stick to steam though, you don't need huge efficiency.

Peter Fairbrother

I got an "Arduino" embedded device working today. Advantage me seeking jobs in processing - new mines opening up around here (Cornwall).

--------------------------------- Congratulations! The bare Arduino doesn't do anything interesting by itself, so a welding voltage and current data recorder might be a good useful project for you. Here's a DC current sensor:

A less demanding initial version could sample, record and perhaps display the audio voltage to a loudspeaker. That would cover most of the user interface, measuring and recording complexity without the risk. A spreadsheet can convert a list of time-stamped voltage readings into a graph, so you don't need to do everything to get started.

Theoretically you can accurately capture frequencies of up to 1/2 the sampling rate. You just filter out the higher frequencies to avoid confusion.

Usually I write the user interface first, as the definition of what to do. It calls dummy routines that return canned responses which I then connect to reality. Having a running program that processes known data can make errors visible as they are introduced.

I never presented myself as a Programmer but the jobs came anyway when the engineers found that I could. Coding plus hands-on skill is uncommon. I've been plodding through a spreadsheet I wrote that figures my taxes. It has several IF;Then;Else structures that gave me some trouble translating them from the text instructions.

Thanks for interesting responses. This whole matter must remain a conjecture. Appreciate you developing this and not leaving it as a "loose end",

I have a "Fluke" meter with clamp to measure Amps - AC and DC. Not the point - you are pointing to a project.

I did think of a device to measure voltage - get it to "stab" in at the torch/gun - and have it speak the voltage so you can run the arc and weld while having the info. I bet there are voice devices for saying numbers?

GnuPlot will graph text files of data - my perception there is no need to keep the data in other than text format. A compression algorithm like "bzip2" can get compress the files ot fractions of the former size

- so easy to keep data.

I've done sampling (?) before:

- MIG/GMAW "waveforms" revealed by datalogging Noting average-Amps x average-Volts does not give average-Power with systematic pulse waveforms.

Arduino - I was rather delighted about "getting" that one. Have programmed in "C" before, so head start. Quickly extended beyond tutorials, using loops "for..." conditionals "if..." to get more interesting things happening. eg. LED's flashing morse-code from tutorial getting an LED to light. Hopefully this will stand as a "proof of concept" and be the start of a progression - hopefully with the adjective "rapid".

I have a "Fluke" meter with clamp to measure Amps - AC and DC. Not the point - you are pointing to a project.

I did think of a device to measure voltage - get it to "stab" in at the torch/gun - and have it speak the voltage so you can run the arc and weld while having the info. I bet there are voice devices for saying numbers?

GnuPlot will graph text files of data - my perception there is no need to keep the data in other than text format. A compression algorithm like "bzip2" can get compress the files ot fractions of the former size

- so easy to keep data.

I've done sampling (?) before:

- MIG/GMAW "waveforms" revealed by datalogging Noting average-Amps x average-Volts does not give average-Power with systematic pulse waveforms.

Arduino - I was rather delighted about "getting" that one. Have programmed in "C" before, so head start. Quickly extended beyond tutorials, using loops "for..." conditionals "if..." to get more interesting things happening. eg. LED's flashing morse-code from tutorial getting an LED to light. Hopefully this will stand as a "proof of concept" and be the start of a progression - hopefully with the adjective "rapid".

---------------------------- Good, you understand the process and its value already. The other obvious use is a robot that crashes into walls and furniture, which is funny with a toy, less so with a heavy Segway bot. The perpetrator had to autograph the damage which was left as a reminder.

I use a laptop and DMMs with RS232 interfaces to measure and record battery charge and discharge. Since they use slow dual slope A/D converters their measuring rate is 1 or 2 per second, which is fine for a steady load, but too slow for the pulsed output of a solar controller. A digital storage scope captures a short sample of the voltage and current pulses for analysis though it won't integrate current into the battery charge level. For that dedicated battery power monitors serve well enough, at least for the steady discharge current. All do some, none do all.

The high price of commercial data loggers prompted me to consider building my own, which would operate at a much higher sampling rate than the DMMs. A Dataq starter kit sort of works but I prefer a higher resolution and interactive control. I had designed and built a fast 16-bit data logger card that plugs into a Macintosh for work, where they wouldn't allow IBM PCs after being embarrassed by a hacker. They gave it back when done and converting it to a printer port interface is on my to-do list. I have experience building and programming high end industrial measurement systems.

Most of the measurements are performed by voltage and current controlled power supplies that report their outputs to the computer, as does this: With battery discharge and welding the voltage drops from high current are a concern. You don't want welding current taking a short cut through the measurement leads. For the ATE we had to limit measurement and return lead currents to a few milliAmps.

That experience served me well when Mitre took up digital radio, which is much like a 2 channel digital oscilloscope. Unlike the radio engineers and techs I knew how to use high speed A/D converters and connect them to a TMS320C30 digital signal processor, I had designed an IC that let both use the same memory simultaneously. Digital radio was the enabler for cell phones.

I bet there are voice devices for saying numbers?

[A simpler VCO tone generator might be enough, it will indicate changes though perhaps not the absolute value, and responds faster. How well do you remember music? I can catch my sister playing one wrong note in a Beethoven symphony, or correct and incorrect start-up sequences in computers connecting via modems over phone lines.]

GnuPlot will graph text files of data - my perception there is no need to keep the data in other than text format. A compression algorithm like "bzip2" can get compress the files ot fractions of the former size

- so easy to keep data.

[[[[[[[[[[[[[[[[[[[[ The CAD programs I used saved everything as text, such as the coordinates of vector lines and the variable settings. I found that very useful for troubleshooting and saved initialization and user settings for the programs I wrote as Variable=Value. Flash and hard drive space is really cheap relative to a simple program's needs.

File handling is much easier on a PC because the operating system manages details. I've done it from scratch on the home computer I designed and had to maintain the file directory externally on paper. Sequential files are easy to process. I wrote a text editor that allowed random insertion or deletion in memory but stored sequentially onto tape.

Nowadays I only cut ceramic turbine wheels on a CNC mill [*] - it has five-and-a-half axes, but I only use three (plus a rotary table) for turbine wheels, that's good enough, so the result is similar to your setup.

For ceramics, don't buy the "machinable" ceramics, they are horribly expensive and their properties are lesser. I get most of my alumina from a no-name chinese source, can be brittle but it is usually ok if yuo keep that in mind. Also Morgan ceramics for high tech and high reliability stuff (Si3N4, ZrO2).

Diamond tooling is not expensive if you a) buy the tools in reasonable quantities and b) keep the water flowing, or even just there. Been meaning to make my own diamond tooling, but I don't know how and haven't really tried - anyone?

NO climb milling is always good :) even in ballscew equipped CNC mills. Somewhat less important when you are using abrasive rather than cutting tools, but still.

Keeping diamond and abrasive ceramic containing slurry out of ballscrews is also good, damhikt.

Peter Fairbrother

[*] technically it's a CNC-converted BCA jig borer, but it has hefty upgraded ballscrews, improved lateral stiffness and is pretty much only used on ceramics with abrasive diamond tooling; though I can fit an ER20 collet shaft and a slower motor. I also have a manual BCA.

[*] technically it's a CNC-converted BCA jig borer, but it has hefty upgraded ballscrews, improved lateral stiffness and is pretty much only used on ceramics with abrasive diamond tooling; though I can fit an ER20 collet shaft and a slower motor. I also have a manual BCA.

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Nice! I have two Henry Hauser vertical mills of similar vintage, unfortunately lever feed for production instead of leadscrew. The seller told me they made WW1 artillery fuses. Did you do the CNC conversion?