Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[gondolier88]

Hi Dave,

Great project, I hope you see it through to the end. Have you got a pic to show us?

At that size you would have enough room to have mechanical control- ie. a feed pump acting off the engine through a bypass controlled by a water sensor on the water gauge with an auto boiler pressure gas regulator controlling the burner.

Greg

[kiwimodeller]

Dave, sounds like a great project, don't forget that we expect a fully illustrated ongoing post as you do the build, just so we have the pleasure of nitpicking any little mistakes you make. Just kidding! But we would all like to see the build. I take it from your description of the engines that you are going to build them as direct acting on the paddlewheel shaft? I am hoping to do the same when I build a model of a New Zealand sternwheeler but it will not be at such a large scale. I am looking at 1:24 and two cylinders of about 3/8" bore and 2" stroke. I am hoping somebody else has or will sort out all the problems before I get started. Cheers, Ian V

[gondolier88]

Hi Ian,

I am looking at 1:24 and two cylinders of about 3/8" bore and 2" stroke.

Very strange cylinder  size- any reason for this in particular? You'd be lucky to get any workable rev's off that- I know sternwheelers don't need a lot of rev's anyway- but I have a feeling that would be excessively slow.

Greg

[Dave_Sohlstrom]

I have to agree with Greg. You are building at 1/2"=1' at 1:24. That would make the real engine 9" bore by 4' stroke seems small for that scale. Portland full size engine is 26" bore and 9' stroke. How long is the full size vessel you are modeling. Portland is 210 feet long, she is a big tug.

Dave

[kiwimodeller]

The original was just over 100ft so not large by American sternwheeler standards. I am not yet sure of the original bore and stroke, still waiting on the plans but the idea of the long stroke was to give good torque and sufficient leverage at the wheelshaft by having the big end a reasonable distance from the centre of the shaft. I read somewhere that small bore long stroke steam engines were slow revving but produced good torque and were still economical on steam as the long stroke utilised all the expansive properties of the steam. Theory of course is not always right and I am ready to change my ideas, in fact it would be easier to have a shorter stroke engine, but would I get away with that without having any sort of gear reduction between the engine and the shaft? I am always happy to blame someone else's ideas when things dont work!

[Dave_Sohlstrom]

Ian

Do you have the name of the vessel you are going to model. It may be possable to find information on line.

Dave

[gondolier88]

You wouldn't need anywhere near the torque required fullsize- remember torque is a square and weight is cubed- go for a shorter stroke- easier to steam, easier to start, and should you need it on the pond- a burst of speed.

Also you could always utilise commercially available stationary mill engine cylinders.

Just a thought.

Greg

[kiwimodeller]

Dave, the vessel is called Manuwai, a Whanganui River (New Zealand) sternwheeler built in kitset form by Yarrows. Model plans are in the process of being drawn up. When I said I did not have the original engine dimensions I meant they have not arrived to me yet but I know they are available and will arrive, there is considerable information about her available.
Greg, I agree it would be much easier to use a shorter stroke and utilise commercial cylinders from someone like John at The Steam Chest who has a great range of engine casting kits that I have been eyeing up and I will do so as long as I can be convinced that they will have enough grunt. We had the discussion at a club day today and the older members are definitely of the opinion that small bore, long stroke engines operating on fairly high pressure and using all the expansive power of high pressure steam will do the job best. Other members, like you are saying that the greater power of more piston area will be more responsive and that I will not need high pressure. It seems quite possible that both would work, the first with high pressure but using a lower volume of steam, the second option using lower pressure but needing a fairly big boiler to make a high volume of steam. It may well be that I need to suck it and see, fortunately it will be a few months before I finish present projects and get on to this one so I have time to read up and canvas opinions on forums like this. Thanks for the input from both of you. Cheers, Ian.

[kiwi]

Hi Ian,
Just for the record
ps Manuwai had a locomotive type boiler rated at 160 lb. (at 140ib propelled the boat at 11.5 knots max speed ), built by Yarrows of London.
And mounted near the bow, consuming 6.5cwt coal per hour from two 3ton coal bunkers either side of the boiler.
Two engines at stern, horizontal with 10.5" bore and 30" stroke, with stephensons link fitted. Operated by telegraph from the bridge. Main steam pipes ran along the underside of the upper deck.
These drove a stern wheel of 10ft dia x 11'-9" width fitted with 10 floats of 9" wide English Elm.
Hull was of galvanised Seimens' mild steel, divide into 7 watertight compartments, each with its ejection pump. On the foredeck was a small double cylinder steam winch for hauling up rapids.

Drawings progressing well, and a friend in the trade is looking at making a fibre-glass hull if your interested, in the size your considering.
kiwi

[kiwimodeller]

Harry, you are as usual a lifesaver and tell that man that I will give my first born son (I've been trying to get rid of him for 30 years) for a glass hull in the right scale  Perhaps you could ask him nicely to increase the depth of the hull to give a little extra displacement to carry heavier (in scale proportions) boilers etc? I have already put aside a nice 9" by 4" boiler which looks the part to try first and am gathering parts and info. Todays effort was to go through my collection of 1940's/50's Model Ships and Powerboats and Voila! I found an Edgar Westbury treatise which discusses engines for different applications and says, in part, "the exception being engines for paddle steamers which, if connected directly to the wheel shaft need to be of small bore and long stroke. Shorter stroke engines need a bevel gear or other reduction to work satisfactorily when driving paddle wheels which rotate slowly". I knew I got the idea of long stroke engines somewhere and this was probably where. Cheers, Ian.

[flashtwo]

Hi all Mayhemers,

At last Vital Byte is back on the water (after sorting out new kitchen/university etc).

Since its last run at Ramsgate, it was apparent that no further software mods were going to improve the performance, so I reconsidered the boiler coil surface area.

In my original calculations I had estimated the surface area of the fire/copper interface rather than the copper/water interface the values being 138 and 84 sq.inches respectively. Obviously the 84 sq.inches was much to small for the D10 engine, so I've rewound and experimented with a number of coils.

The original was 5 metres of 1/4inch O.D. 18 swg copper and I have wound three additional coils  of 7 metres of 1/4inch 20 swg (142 sq.inches approx), 9 metres of 3/16inch 22 swg (149 sq.inches), and finally 15 metres of 3/16inch 22swg (240 sq.inches), experimenting with each of the coils in V.B. on the test pond (hasn't the price of copper gone up!).

I managed to get all 15 metres of the 3/16inch into the original boiler casing by winding the coil into three layers. It took an hour and three quarters to wind the coil (including a joint to connect the 10 and 5 metres sections together), turn two adaptors on the lathe and fit it in the boat.

The other change to V.B. is the use of a five inch prop, with the proper blade twist, kindly on loan from Malcolm Beak.

Today I steamed V.B. down at Mote Park, Maidstone and she performed extremely well with the 15 metre coil, showing a very powerful bow wave. The hull wave crested at the bow, midway and stern.

She had two runs of 28 and 38 minutes, RPM peaked at 610 and averaged 394. On both the runs the gas consumption was 4grams/minute. The acceleration was very good.

The gas cylinder pressure was monitored. It started of at 2.5bar, which obviously gave the best performance, and was still perfoming well when the gas supply was down to 0.6bar.

Well, I've run out of ideas now to improve what is now a very satisfactory performance, other than putting the plant into a proper hull.

On to the next project - a steam jet powered boat?

Ian

[kiwimodeller]

A steam turbine pulling 35,000 revs would sound good! cheers, Ian 2

[gondolier88]

Hi Ian(s),

Turbine very interesting suggestion- have you seen the Tesla Turbine- kind of a percussive turbine using flat discs- but the 10inch(?) model produced around 30HP- imagine if you could use ultra-thin blue steel discs around 1.5inch Dia. running around 30,000RPM- drive through a half reduction gearbox to give useable and powerful engine.

Also- as you obviously like an experiment- have you seen the Brotan-Defner loco type boiler? Basically an efficient 3 drum watertube boiler forms the firebox, the top drum ,however, is joined to the top of a sloping barrelled conventional locomotive firetube boiler- having a tubeplate at either end though. This mean that at the point of the most heat- the firebox- you have extremely efficient heat transfer- massive surface area, low water content, fantastic water circulation- then the firetubed barrel uses the cooler gasses at a slower speed- extracting the useful heat left. The bottom drums of the watertube boiler are both connected to the barrel by extension tubes curving upto the bottom of the barrel giving increased water circulation.

Steam is taken off the top of the barrel slope or the top drum of the firebox- the thing is the variables with this boiler are numerous- tube diameter, number of tubes, length of tubes on the water tube side- barrel diameter, firetube length, firetube diameter barrel length- also a superheater of the Schmidt type could be fitted (the same type as fitted to the last types of BR express steam locos).

Basically a really developable boiler, could be made super heat efficient and also an interesting engineering project, something to thimk about.

Wikipedia and Google bring up results if you search Brotan boiler and Brotan-Defner boiler.

Greg

[flashtwo]

Thanks for your ideas guys - they're much appreciated.

I was actually thinking of building on my flash steam boiler experience and having a zero reving "engine", i.e. a pure jet with no moving parts apart from the feed water pump.

The ultimate aim is a steam powered Bluebird K7 (but with better high speed stability!) - wishful thinking perhaps, but I might learn something new on the way.

I've just started on the feed pump and I shall be using the boiler coils from the Vital Byte experiments.

The Vital Byte will still be in the frame though, since I want to reduce the computer size and extend the endurance. Currently VB is run time limited by the engine exhaust oil trap filling up and the displacement lubricator becoming empty. At a gas consumption of 4grams/minute, the 460grams in the gas cylinder, fuel supply is not a limit for extended running.

One question I have for those with conventional boilers is that when the water level drops in the boiler, does the heating surface area between the copper and water reduce thus affecting the performance of the boiler and engine and is it noticable?

Ian

[kiwimodeller]

Ian, the theory seems to be that with the common types of comercially made boilers available a vertical boiler is more affected by loss of heating area in contact with the water as the level drops than is a horizontal one. A horizontal single flue boiler with cross tubes in the flue would have to be down pretty low before there was a noticeable amount of the heating surface area not in contact with water. In my limited experience other factors such as the drop in gas pressure due to the drop in gas cylinder temperature have far more noticeable effect on the performance of commercial model boiler setups. Cheers, Ian V.

[gondolier88]

Hi Flashtwo,

Steam powered K7 isn't too much of a far-fetched idea- in 2007(?) a flash steam powered hydroplane was entered into the Coniston Water Speed Trials- however although it had worked really well on experimental runs, on the day it failed to perform.

Greg

[SteamboatPhil]

The full size flash steam hydroplane will be returning to Coniston this year to have another bash at the record. I gather that John has ironed out all the bugs he had in 07.
I will keep you up to date on his progress.

[flashtwo]

Phil,
Has the Coniston flash steam hydroplane got a website - I'm intrigued. Regarding Vital Byte, I've got the feeling, since now I've 45 foot of tubing, that the traditional flash steam boiler really over-fires the boiler to achieve red hot coils and true flashing off of the steam rather than a boiling off. Do you calculate steam production in the traditional way of surface area of the copper/water interface or is it more a matter of burning as much fuel as possible? The point is my plant seems to be so tame (though still very effective) compared with the performance of your straight runners and the tethered variety or are they completely different animals.


Last Saturday, I remade the D10's slide valve push rods, since the originals had too much vertical play in them for accurate valve timing. On Sunday at Mote Park, the test run was a total failure due to the slide valves themselves not seating, consequently letting by all the steam. (club member Richard was there again, strangely coincident with major problems with VB!)

I discovered that, although the vertical slack had been eliminated, there was not enough clearance between the slide valves and the adjusting nuts, causing them to bind. By use of a fine file, enough clearance was made, timing reset and the slide valve seating was tested by applying suction to the respective exhaust port.

VB was run in the test tank and peaked at 642RPM and averaged 465RPM over an 11 minute run. Ready now for another run on the lake.

With regard to hull speed, I understand that is achieved when there is an equal  bow and a stern wave with a dip halfway along the waterline. If there is a wave halfway along the waterline does that mean it is going at half hull speed, or is it an indication of an efficient mode of running?

Ian G.

[gondolier88]

Hi Ian G,

Wow you are getting into hull design as well as experimental steam eh!!!

Ok, a steam hull should always have the most efficient hull design possible. Indications of efficiency are-

- Little or no 'hull wave'- the bigger the wave the more the water is being pushed out of the way as opposed to being 'run over'.
- Bow lift- means displacement is in the right area- if the bow cuts in and down the displacement is dragging and needs more power.
- Stern stays bouyant at hull speed- the more it sinks the more wake is made and this just wastes power.

These go for displacement hulls only of course.

These are the two most efficient hulls in the SBA...currently !

1- Arlette- 31ft single chine plywood with loco boiler and single cylinder thornycroft engine 3 3/4" x 5"(?)
2- Oberon- 29ft strip plank cedar hull, 3-drum LIFU boiler with 2 1/2" + 5" x 4" LIFU compound.

In the pics they are both running at full speed- this is Arlette- 16mph and Oberon- 14mph- both engines run around 600-700 rpm- do the maths with the engine's power and you can see how efficient these boats are.

Greg

[kno3]

Where are the pics?

[gondolier88]

Ahem...

Thanks Kno3

[flashtwo]

Hi Mayhemers,

Warning: this post contains computer speak!

Whilst waiting for some fine weather to test Vital Byte, I've started on the new control computer (designated the AE35 unit) which, hopefully, will be about a third of the size of the original and will fit into a smaller range of boats.

I'm also taking the oportunity to strip out a lot of redundant code and give the data displays a better layout. The AE35 will be using serial communication between the chips in place of parallel comms and the dedicated analogue and digital signals.

The test board for learning how to use serial comms is working and I'm now migrating the RPM software into the PIC chips for testing.

Previously I was using 40-pin PICs for measuring the pumps and engine RPM and have now replaced them with 18-pin PICs, thus saving a lot of room. Also, one of the original 40-pin PICs was totally redundant.

When using parallel comms, the Veroboard had 15  tracks dedicated for communication - using serial has reduced this to just four, thus another space saving measure.

Hopefull, Vital Byte will be testing its new "brain" (the AE35) before Christmas.

Meanwhile, back in the machine shop (shed!), the feed pump for the steam jet engine is nearly complete and the boiler casing will be started on soon.

I'm up at the Warwick International Model Boat show on Sunday, flitting between the Maidstone Cygnets stand ( with the 13ft HMS Kent)  and Blackheath's stand chatting with Phil Abbott about --- flash steam - what else!

I hope to see some Mayhemers there.

All the best

Ian G.

[steamboatmodel]

Hi Ian,
Re "The test board for learning how to use serial comms is working and I'm now migrating the RPM software into the PIC chips for testing. "
What is RPM software? Assembly, Basic and C I have played around with, but RPM is now to me. Also what chips are you using?
Regards,
Gerald.

[flashtwo]

Sorry Gerald,

I should have said the RPM (revs per minute) code that was used on the original computer control system. It is written in the Microchip PIC assembler.

The main workhorse of the board is the 16F877. I have one for display purposes and another for the actual control of the feed water flow and steam temperature. I've replaced three other 877s with 16F819s, to save space, and I have one 16F628 as a clock for timing the pump and engine RPM (it eliminates a large interrupt burden).

The chips are now linked with serial communications whereas before the RPM values were sent as voltage signals and other data as a simple digital signal.

Ian G.

[steamboatmodel]

Now things are clearer. I have one of Microchips PIC kit 2 programmers and a couple of there development boards which I intend to play around with. I have been waiting untill I get another computer that I can put in the shop to do the experimentation on as soldering and breadboards don't go down too well in the living room where this computer is. Until then I have been doing some studying and reading on the PICs.
Regards,
Gerald.