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[kiwimodeller]

Hi, I am about to start on the next project, a River Queen powered by a Gage twin and want to use a vertical boiler for the first time although I have had several horizontal boilers. I have been offered two different designs of boiler and burner and do not really know which would be best or how to choose between them so I am hoping there will lots of answers with a clear decision on which is best. The first one I have been offered is virtually a horizontal boiler stood on its end. It has a single central flue with cross water tubes. There is a 90 degree bend at the bottom of the flue which passes out through the side of the casing and it has a 1 & 1/4" ceramic burner just like one for a horizontal. The other has five small flue tubes up through the boiler with a coned cap on the top leading to the funnel. The burner is a 2" round ceramic in the lower chamber beneath the boiler. It seems to me that the second one is the traditional style of vertical boiler but the chap who makes the first one says he has compared them side by side and his new design makes more steam and gets up to pressure faster. Opinions please! Thanks, Ian.

[kiwimodeller]

Having gone net surfing after posting this question it seems that the first type of boiler and burner are made the same way as Maccsteam make their vertical boiler so perhaps there is something in what the builder says?

[steamboatmodel]

Hi Ian,
What is the vertical height of each of the boilers?
I would go with the one with the lowest height. Peter Arnot had published a design for a center flue boiler in Model Boats that you could use either horizontally or vertically, I have a copy of it around somewhere that I could send you.
Regards,
Gerald.

[kno3]

If the River Queen is what I think, that is an American stern-wheeler, then a vertical boiler might not be the best, since it has a high centre of gravity which, combined with the ship's shallow draught, would make it unstable.
I would suggest using a horizontal boiler.

[gondolier88]

Hi Ian,

I agree with Kno3, a horizontal would suit the boat better, however to answer the question you ask;

boiler 1 advantages- if they are a similar size then pint for pint then this one will have a higher water content, so would be a steadier steamer, however...
boiler 1 disadvantages- cross tube boilers are NOT quicker steamers than multitubular designs- unless there is a huge amount then the heating surface just can't match firetubes.

boiler 2 advantages- from your description this boiler would suit an open boat much better as the burner is more contemporary with full size design. This one will be a quicker steamer.
boiler 2 disadvantages- water won't last as long.

Greg

[kno3]

Ian, I have read a book about boiler making which says that vertical fire tubes are not as efficient as horizontal fire tubes or water tubes. So what your boiler makier is saying, about the boiler with cross tubes (water tubes) being the faster steamer seems quite plausible.

[gondolier88]

Hi Kno3,

Watertubes and cross tubes are two very different things- watertube boilers have literally hundreds of small bore tubes with very low water content giving good heating surface to water content and some of the fastest steam raising you will ever see- try 0-250psi in 8mins for a 30HP boiler with liquid fuel firing!

Cross tubes are large bore pipes that cross from one side of a single vertical or horizontal flue to the other- making what is in effect a horendously inefficient design into a good design, but still nowhere near as good as a vertical, or as you correctly say, horizontal firetubes.

Horizontal firetubes are more efficient than vertical ones due to the fact that they are fully submerged unlike vertical ones which have no effective heating surface above the waterline and also the products of combustion move slower through a horizontal pipe than vertical.

Greg

[derekwarner]

A question for Nick Monahan.......hi Nick..... you do both horizontal and vertical [cross tube] boilers.......I have posted a cross section drawing of a vertical boiler which I believe is pretty standard type construction

We see that whilst being vertical in design, it has cross tubes at 90 degrees to both the horizontal and vertical plane heat gas path......if thats makes sense  

From your experience......... ...is there any significant thermal output variance between vertical to horizontal boiler design.....in these model application boilers?..............

I see where Greg is coming from.....in my case when the boiler is say 1/2 empty.....the heat on tube sets a) & b) are doing little   ..... with only tubes @ c) being fully covered ........

However more thinking . suggests..... that the only real saving would be on gas & that is only if the boiler burner gas supply was auto pressure regulated ????????????????? Derek

[kiwimodeller]

Thanks for all the interest. Just to clarify, the River Queen I am talking about is a Vic Smeed design for a clinker built open launch. Also when I talk about water tubes I am meaning smaller tubes which are across the main flue. Further reading suggests that for the same dimensions the horizontal boiler is more efficient due to all the tubes being below the water level (at least until the level gets dangerously low) whereas the top cross tubes in a single flue vertical are out of the water once the level drops. The horizontal also has a lower centre of gravity which could be an advantage too but given that the original boat had a vertical boiler I would still like to consider one. The question really is whether a vertical boiler with several smaller diameter vertical flues and a large diameter burner in the firebox would work better than a vertical boiler with one large central flue, cross tubes and a burner the same diameter as the flue? It seems that the sort of design drawn by Derek is more traditional and has been around for a while whereas the latest idea seems to be almost a horizontal bouiler converted to stand on its end. If I do decide to go vertical at the moment I am inclined towards the traditional with about 5 smaller diameter vertical tubes. Cheers, Ian.

[kno3]

Ok Ian, I was thinking about a sternwheeler
Since your boat is an open launch, choose the boiler that you like best, provided it suits the launch and doesn't make it too top-heavy. Regarding style, I guess that both boiler types you are considering look pretty much the same, the exception being the burner position.

You could try measuring the heated surface of both boiler types you are considering and see which is better (you need to consider the water-covered surface though). But if you trust the boiler maker, then follow his advice, he should know which is the faster steamer.

[MONAHAN STEAM MODELS]

A question for Nick Monahan.......hi Nick..... you do both horizontal and vertical [cross tube] boilers.......I have posted a cross section drawing of a vertical boiler which I believe is pretty standard type construction

We see that whilst being vertical in design, it has cross tubes at 90 degrees to both the horizontal and vertical plane heat gas path......if thats makes sense  

From your experience......... ...is there any significant thermal output variance between vertical to horizontal boiler design.....in these model application boilers?..............

I see where Greg is coming from.....in my case when the boiler is say 1/2 empty.....the heat on tube sets a) & b) are doing little   ..... with only tubes @ c) being fully covered ........

However more thinking . suggests..... that the only real saving would be on gas & that is only if the boiler burner gas supply was auto pressure regulated ????????????????? Derek

Hi Derek,

You have asked a great question and I will be happy to thoroughly answer your question in finite detail once I have a free moment to dig myself out of the mountain of work that I am under presently. What I can say for now is that a boilers efficiency from one design to the next is relative to a number of variables in each design. I am afraid that there's not a simple generic cut and dry answer to this question. We will have to get into burner designs also to thoroughly answer this question.

Best Regards,

Nick

[gondolier88]

Hi all,

If i've said it once... go on amazon/ebay etc. and buy yourselves a copy of KN Harris's book 'Model Boilers And Boilermaking'- this book answers absolutely everything you will ever need to know about boilers, and more!

It sounds like this is where Kno3 is getting his facts from and is absolutley correct- mixing up watertubes and cross tubes aside.

Put it this way- if you had a selection of boilers of differing types but of the same VOLOME by water, the efficiency scale reads roughly thus (from worst to best);

vertical single centre flue no firebox
horizontal single flue
vertical single centre flue no firebox with cross tubes
vertical single centre flue with firebox
horizontal single flue with cross tubes
vertical multitube firetube
horizontal double pass single flue
horizontal double pass single flue with cross tubes
vertical single centre flue with firebox and cross tubes
vertical multitube firetube with firebox
vertical single centre flue with firebox and cross tubes and 'field' tubes
vertical multitube firetube with firebox and 'field' tubes
horizontal double pass multitube dryback
horizontal double pass multitube with cross tubes dry back
horizontal double pass multitube wet back

Now of course there are many variants on a theme, and I haven’t included water tube, locomotive, Yorkshire wagon type, sentinel wagon type, cochran type or any other you care to mention.

Also much efficiency can be gained by adding external heating surface- superheater, feed water heater etc.

Greg
 

[kno3]

Greg, yes I read that in K.N.Harris's book too. Now water tubes and cross tubes are and aren't the same thing, depending on how they are made.

Your list of boilers by efficiency is quite interesting. Where did you take it from?
And do you mean efficiency as in using the least amount of fuel to boil the same volume of water, or as in being the fastest steam producer regardless of fuel spent?

[gondolier88]

Hi Kno3,

The list is made purely from a heating surface point of view- all other things being equal- ie. volume of water and burner output- so the first would be slower to raise steam and wouldn't supply it as quick as the last boiler ion the list.

Of course you can make a slow steaming boiler very EFFICIENT by lagging it thouroughly, making sure complete combustion is taking place and add feedwater heaters and superheater, but you'd still have a slow steaming boiler in comparison to one with a greater heating surface.

I'm sure it's in KN Harris's book where the qoute 'a boiler's efficency is it's capacity to boil water quicker using as little fuel as possible'- the only way it can do this is by having as much good heating surface as possible- good burner design and lagging of course complete the equation.

Greg

[derekwarner]

Hi Guys.........Nick ...I think we have an understanding here on relative merits  & all things being equal....so please do not stop work just to comment in detail

I suggest from the points offered ..........

1) if your prototypical vessel used a vertical boiler...then use a model vertical boiler
2) if you really need to harness all of the possible steam output for heat input....the add the equal boiler weight in insulation & loose the intention of the model boiler visual appearance

Happy steaming......efficient or not  ........Derek

[kiwimodeller]

Great input thanks guys and that list (even if I do not understand what all of them are) is the best summary I have seen. A friend has just rung to say he has the Harris book so I am off to get it and learn enough to make up my own mind. It does seem that most of the commercially available boilers are the usual compromise between efficiency and manufacturing cost but it also seems that they are good enough to do the job provided you pick the right one and the right size. Thanks for all the help. Ian.

[kno3]

Hi Kno3,

The list is made purely from a heating surface point of view- all other things being equal- ie. volume of water and burner output- so the first would be slower to raise steam and wouldn't supply it as quick as the last boiler ion the list.

Of course you can make a slow steaming boiler very EFFICIENT by lagging it thouroughly, making sure complete combustion is taking place and add feedwater heaters and superheater, but you'd still have a slow steaming boiler in comparison to one with a greater heating surface.

I'm sure it's in KN Harris's book where the qoute 'a boiler's efficency is it's capacity to boil water quicker using as little fuel as possible'- the only way it can do this is by having as much good heating surface as possible- good burner design and lagging of course complete the equation.

Greg

Hi Greg, the interesting fact (as described by Harris) is that vertical fire tubes are not as good at thermal transfer as horizontal ones, not only because they are not completely submerged, but also, I think, because the gases move faster in them and transfer less heat.
That's why some resorted to stuffing metal gauze or twisted pieces of metal sheet in vertical flues (especially in single flue vertical boilers). This apparently hinders the direct flow of gas (upwards), creating a vortex that improves thermal transfer.

[malcolmbeak]

Hi Ian
For those that don't know, I've included a picture of my River Queen. It is 36" long, nominally 1/8 scale and powered by a 3/8" bore and stroke twin and uses a forward - neutral - reverse gearbox instead of reversing the engine. As far as the boiler is concerned, I've copied out what I wrote about the boiler for an article about the boat several years ago.

"Thinking about the full size boat, a vertical boiler with a maximum overall diameter of 3 feet and a height over the casing of 4 feet should look about right. After hunting through the assortment of available copper tube, a suitable piece of 16swg some 3⅛″ diameter was located. For some time I had been toying with various heating tube arrangements, and finally decided on that shown. The central flue is 1⅝″ o.d. x 16swg, and the 12 circulating tubes are 3/16″ o.d. The maximum water depth is 3″, just below the circulating tube outlets. This gives a total heating area of about 30 square inches. One advantage with this design is that the whole boiler with the exception of the top plate can be assembled, silver soldered, and checked for circulation with a suitable burner. The answer was excellent. With only an inch of water in the boiler, it came gushing out of the circulating tubes. The boiler was therefore completed with ferrules for the various connections that I expected to fit: - Water gauge, water feed, safety valve, pressure gauge and main steam pipe. A concentric superheater was made to fit down the centre of the ring of circulating pipes. This consisted of an ⅛″ pipe feeding steam from top to the bottom of the ⅜″ return tube. The steam therefore travels relatively slowly gaining a lot of heat. Originally the superheater was 3″ long reaching well into the flame, but when first steamed, the nice red paint on the steam line fittings turned black, and the soft packing round the pistons was no longer soft. I’m not sure why the plug silver soldered in the lower end if the ⅜″ tube didn’t blow out. So an inch was taken off the end, and the plug brazed in this time. Now the paint has just gone a dark red! The boiler is lagged with mahogany strips held on with brass bands. The top is covered with a shallow conical cover into which is riveted the funnel. The exhaust is directed up the funnel with the end of the pipe being belled to give a “soft” exhaust. In the past I had had trouble with exhaust blast pulling the flame off the burner and extinguishing it."
Malcolm

[Circlip]

You gotta be a masochist with TWELVE swaged tubes Malcolm,  for most, THREE on the simple Smithies is bad enough   

  Regards  Ian.

[kno3]

Malcolm, that's a very nice boat and boiler. What burner do you use and how does the boiler perform?

Would you care to explain the building process a bit, I'm especially interested in how to drill the centre flue for the curved water tubes?

[malcolmbeak]

kno3
It was over 20 years ago I made that boiler, so this is what I seem to remember I did.
I assume you are OK with the outer shell and ends. The flue and circulating tubes were made as a separate unit then assembled with the other parts. As far as I can remember - the ring of twelve holes at the upper end are no problem. for the lower holes I drilled them as for the top, then with the copper well anealed a short steel mandrel was inserted into the lower end and a piece of 3/16 steel rod into one of the holes then lent on until the flue was deformed into the desired shape. Repeated for each hole, anealing as required. the end result wasn't pretty! But it worked. The circulating tubes had been bent up previously and trimmed to size. They were then assembled and silver soldered in place. In later boilers instead of a single bend in the circulating tube, they were bent into a very shallow "U" shape. You have to be accurate with the bending, but plain holes are all that is needed in the flue. Circlip - there are no swaged joints, juse silver solderer.

The burner is a circular one about 1 1/2" dia. The top is conical - about 120 degree I think and about 1/16" thick (keep it thicker than the hole dia). There are three rings of 1mm holes. I believe there about 50 in the outer row and obviously less in the inner ones. The idea was to keep the circular pitch the same in all rows. The gap between the edge of the burner and the flue is very small. In fact most of the air is taken in as primary just after the jet, and it wont burn out of the boiler. It is lit at the top of the funnel - sometimes needs a few attempts until there is a little heat there. This was before there was much use made of ceramic burners, and I guess that one of these would be at least as good as my system.

It all seems to work pretty well. The big advantage is that even with the water level low, provided it is above the lower end of the circulating tubes there is such good circulation that there is still a reasonable heating surface. I think the tubes provide more effective heating than the flue surface.

Malcolm

[gondolier88]

Hi Malcolm,

I didn't make the connection until now- was your launch documented in model engineer a couple of years ago? I remember your boiler design and beautiful hull (not your design, if I remember correctly?), and also you had an interesting boiler water level control I think?

Hi Kno3,

Hi Greg, the interesting fact (as described by Harris) is that vertical fire tubes are not as good at thermal transfer as horizontal ones, not only because they are not completely submerged, but also, I think, because the gases move faster in them and transfer less heat.
That's why some resorted to stuffing metal gauze or twisted pieces of metal sheet in vertical flues (especially in single flue vertical boilers). This apparently hinders the direct flow of gas (upwards), creating a vortex that improves thermal transfer.

Erm, I think I mentioned the products of combustion velocity difference between vertical and horizontal in an earlier post- but you are quite correct. Also your pointing out the use of baffles in flues is an interesting one- for a while this technique was used in domestic 'thermal stores'- the design I know most is the 'powermax'- only by ripping them out to replace with more efficient combi boilers- however these were built very much like a model steam boiler- they are full copper construction, with a horizontal fanned burner firing into a sealed combustion chamber, from where the gasses are directed upwards into 9 x 1" copper tubes- about 2.5' long-, in each of these tubes was placed a stainless steel baffle- starting off as a straight piece of stainless steel about 7/8" wide by 2.5' long by 1/8" thick- this was first twisted with a pitch of about 5" between twists, then each twist had tabs of about 3/8" pushed out every couple of inches or so, to look at the design it 's safe to assume that the twists make a longer path for the gasses to take, so slowing them down, then the tabs create turbulance and a quicker transfer of heat as these break down the 'boundary layer' between the gasses and copper, they work well until they burn out!

Basically Kiwi' go for the lightest design with the most heating surface to water volume ratio- but as it's a model open launch, make sure it's good looking too, you should then fill all your needs.

Greg

[malcolmbeak]

Greg
Engineering in Miniature - several years ago.
That article, the waterlevel control and several others are available as downloads on the Paddleducks site.
But you have to be a member and have made a few posts before you have access to them.
Malcolm

[Circlip]

Sorry Malcolm, difference in terminology, I meant the lower ends of the tubes and the hole and bar trick.

  Regards  Ian.

[kiwimodeller]

Malcolm, I have a download of the article on the developement of the Cyril thanks (along with several other drawings you sent and the sizing article). A friend has just begun building the gearbox (I am going to use a variable prop) and I am doing the throttle valve at the moment but having only done a couple of simple boilers the thought of trying to copy your boiler scares the cr_p out of me. Even my more experienced friend was not game to try it. I think I will probably chicken out and use a horizontal with a flue and cross tubes although I might be tempted to go to your design with no cross tubes (so I can use your slot type burner) and then fit the small return tubes and have the funnel at the same end as the burner. If not this boat then sometime soon. Thanks for your help. Ian.