Are water-tube boilers actually easier to build?

[hartleymartin]

I've been looking around on the interwebs for information about boiler-making, and I've seen a large number of claims that water-tube boilers are actually easier to build than fire-tube boilers. Is this really the case? Should I seriously consider getting a design for a small water-tube boiler rather than a vertical fire-tube one?

I've also been told that water-tube boilers are safer in that they don't explode, but rather tend to fail by springing a leak. Would a fusible plug in the main steam vessel still be a good idea?

As you can tell, I'm a complete newbie at this, having come from a background in small sail craft from my time as a Navy Cadet. (Weekend "puddle-pirate")

I'm interested to find out as much as I can. I remain interested in building a simply plywood boat and kitting it out as a small steam launch (I think a "messabout" is the right term for the sort of boat I want)

[Scotty]

Easier to build ...
I wold not say so. You have to take into account all the various parts of the system called boiler
(pressure part, furnace insulation, lagging, accessability and so on).
Both types are complicated to build if you want performance with reasonable weight and good efficiency.

Safer ...
There is no argument for the safety of one kind of boiler being higher than the other.
For every accident there has been a reason, sometimes difficult to analyse.
Reasons have been bad handling, bad design, bad material and bad workmanship,
some boilers have simply been over age - regardless of type.

Just design (and build maybe) the boiler you like and which is appropriate for your boat.

After a handful of firetube boilers in the last 25 years I design now two watertube boilers
and I find (not surprisingly) they are no more and no less difficult.

Scotty

[Lopez Mike]

I would make my decision based more on other issues than the construction difficulties. This coming from a person who knows little of water tube boilers and has never built one.

Center of gravity on a WT unit might be lower.
FT boiler usually has more water and thus reacts more slowly. A nice thing.
No tube bending in a FT unit usually.
WT unit might be lighter? Not sure.
Maybe easier to build a WT unit that is narrower and easier to get past in a narrow boat.
I find a fire tube boiler easy to machine.

In both designs I always have any weld under significant stress done by a person certified as at least a pipeline welder if not pressure vessels.
Probably the main drawback to a fire tube boiler is boring all those holes in the tube plates. CNC would be nice. A mill works well as much because it can turn slowly and use power feed. The need for accurate location of the tube holes is much exaggerated. Laying out with common drawing tools followed by a center punch and free hand location works fine.

In either design, be generous with insulation. Few small boilers are well enough insulated.

[malcolmd]

The SBA and John King (SBA member) have some nice designs for WT boilers, and some are "weld-less" so can be built by the non-welder. I am building (not started it yet) Yarrow type, and have seen a couple built and the builders found them "simple"... THere is a great blog on building one (in NZ) but I can't remember the URL (sorry).

They do hold less water, and so are perhaps well suited to liquid fuel (as implemented in the 1900's by people like SimpsonStrickland) and LIFU

[DetroiTug]

After being involved with a VFT build and building an Ofeldt water tube, I would say the work is about equal if built properly. What someone may have meant by water tube types being easier to build is they actually meant monotube boiler, they are typically pretty simple construction.

Both boilers if constructed correctly, from the proper materials and operated withing their design parameters are very safe. The water tube is typically safer though - being able to withstand much higher pressures. It's a moot point though as the difference is for instance, 1200psi WP vs 2000psi WP. No steamboater runs those sorts of pressures.

Stanley cars use a VFT and run in the 600psi range. With thousands of them being produced, there is no record of a Stanley boiler ever exploding in normal usage. One was taken to failure at the factory and the explosion blew most of the windows out of the building.

On my Locomobile steamer nothing gets my attention like kneeling down under it messing with the burner and have it pop off at 250 psi which vents straight down on the other side of the car. Scares the heck out of me

-Ron

[mtnman]

Reading the book "Steamboats and Modern Steam Launches" Edited by Bill Durham, I ran across an article about Porcupine boilers, "Porkys". They seem extremely easy to build, almost no welding required, just boring and threading. Anyone here have any experience with a porky?

[fredrosse]

From a previous topic "Why no Porkies?":

One of the keys to reasonable boiler life is maintaining strong circulation throughout the steam generating tubes. As Mike mentions, Porcupine Boilers need to have internal baffles to promote circulation, yet even with this feature the circulation is not as good as with other boilers that have a definite inlet and outlet for each boiler tube.

Another feature of Porcupine Boilers is the increasing flue gas flow area at the outside diameter of the Porcupine Boiler. This results in most of the flue gas traveling at the outer regions of the boiler casing, and the Porcupine tubes near the drum are starved from hot gas flow.

I think the historic reason for some popularity of Porcupine Boilers is the ease of construction using screwed pipe nipples, before arc welding or brazing was generally available. Today with modern welding and brazing equipment very available even to we amature builders, the better arrangement and less boiler tube connections of an Oldfeldt, Bolsolver, or similar boiler makes these types the clear choice over the Porcupine Boiler.

[hartleymartin]

Of course, my other problem is that I don't know any dimensions for building such a beast. As far as I can find, you can only obtain suitable copper pipe/tube for pressure vessels in up to 8" outside diameter with a 2.8mm wall thickness.

It seems that even if I built a simple water-tube boiler with this as the main steam drum, I might only be able to power a small single-cylinder engine inside a 10' dinghy!

Can anyone give me some indication as to the sizes of the various components of a small water-tube boiler? Information seems a bit scarce online, especially as I don't really properly know what I'm looking for.

[marinesteam]

Unless you understand the engineering involved I would recommend staying away from designing and building your own pressure vessel. Al least if you plan on building your own, stick with known, proven designs and have a means of verifying that your construction techniques are sound.

The boiler codes are based on the lessons (failures) of the past and are in place to keep all safe (though not the only knowledge needed to do so). Anything that is capable of being a power plant for even the smallest launch needs to be built to the minimum design considerations specified in the code. The necessity of having the boiler designed and built by persons with qualifications in doing so is also dictated by the laws of your locality. The code is only a guide the minimum design requirements needed to be safe and must be followed regardless of if the boiler is to be a "stamped code boiler" or not.

We're happy to point you in the right direction but I don't think anyone here is going to make recommendations on boiler component sizing. I suspect that the reason that there is little information online is that the liability is just too high. Good plans don't guarantee a good, safe boiler as a poorly built boiler is just as unsafe as a poorly designed one. There are some options, as mentioned the SBA boiler library is a good place to start as there is a wide range of boiler plans available including smaller weld less water tubes. The scale loco people would be good resource for the smaller boiler designs you're looking for as well. And there are built boilers available from reputable sources like those that sell steamboat items (Beckmann or Mosquito, etc).

I don't want to make the steam sound like it's one only for the rich man as there are plenty of ways to be frugal and successful but it isn't a hobby that can be done on the cheap especially where the boiler is concerned. I'm also not saying that one can't build their own boiler as there are many examples of "home" built boilers in operation. I suspect the successful home builders have done lot's of research, and/or already had the knowledge, and/or have had assistance when tackling a boiler build. The trade off is time or money. If you are to take on a boiler build you need to do the work needed and to spend the money to ensure that it's done properly. It's not as simple as just asking what size pipe to use. A boiler build is not a place to skimp whether it be on materials, proper safety appliances and it's certainly no place to learn welding technique. Sorry if this comes off as being harsh but it's important for your safety, the safety of others and the continued enjoyment of our hobby for all that participate.



Cheers

Ken

[hartleymartin]

Indulge my love for theorising for a few moments.

Let's say that I attempt to build a simple water-tube boiler. The steam drum is a 6" or 8" diameter copper pipe which has had the ends capped in some way which makes it a suitable pressure vessel. This would be connected to two "mud drums" say 3" diameter. Would it work if at each end there were, say 1-1/2" diameter pipes, and in between there were a series of smaller diameter pipes, say 1/2" diameter. The larger pipes would be where the hot water circulates down to the mud drums and the smaller pipes would be where the water is heated.

To add extra heating surface, a number of pipes coming out of the bottom of the steam drum, and angled upwards from the back to the front (i.e. to promote circulation)

Could this work to power a small single or two-cylinder compound for a small steam launch?

This is a theoretical exercise in finding what is the simplest and smallest boiler for this purpose.