An Outboard steam engine in Forsvik - by Anreas Hübner

Translation and editing by Dietrich Schacht

Sven Olof Carlberg was a brilliant inventor. He lived in Karlsborg, Sweden, and passed away in May 2004. On one of my trips to the Industrial Museum in neighboring Forsvik I was privileged to to get an insight into his work on the occasion of the 'Kulturhusens dag' (on this one day of the year the Museum focuses on one specific activity of the Swedish people. The main theme changes every year).

I traveled to Forsvik to attend an event on the topic "Maritime Heritage". To participateI I followed the Theme with my model steam tug "Michel". Additionally,  Steam model makers were invited from all over Sweden. When setting up our exhibition stand I was amazed when the friends from the Museum opened their boxes and unpacked their well kept treasures. Mr. Carlberg was obviously also inclined towards model building and had a collection of steam powered model ships, model diesel engines and model steam engines on display. Of course there was a special table in his honor (picture 2).

It will interest us later that all his Steam boilers were continuous flow boilers, some with two coils. The models were not all ready for demonstration, but I will  remember some objects for a long time and come back!

That day, for me, the most remarkable and curious exhibit of the Collection is shown in Figure 3 by the "First Steam Boat Captain”, Lasse Sundström presenting the 'Utombordsång maskin (outboard steam engine)' or – in short – the steam outboard. Later it was assembled and fueled on a rowing boat and went into service with no complaints. After initial difficulties – I already had offered tug help (picture 4 below) – he drove the boat lap after lap over the Bottensjö. (Picture 1 above) to see how it makes noise in the evening sun steaming across the lake.

A weekend later, on the occasion of a meeting of the Sveriges Ångbåtsförening (Swedish steamboat club) at the same place, I had the opportunity to deal with this machine in detail, to present it to the 40 colleagues who had traveled, to explain it and to operate it. Figure 5 shows a hand sketch that identifies Sven Olof Carlberg as the designer and builder of the outboard engine in the 1950s. However, the drawing is not by him, but was reproduced later. This also includes an instruction manual (my "Bible" for the day), which deals in detail with the preparation for steam operation, the operation itself and the subsequent care of the device. The sketch was allegedly created by an unknown author in the 1970s after personal contact with Mr Carlberg. In any case, some experience with the machine has been gained since then, which has been incorporated into the instructions.

All parts of the outboard are compactly accommodated in a common housing in the form of a tin cylinder, at the upper end of which are the chimney and the combustion damper. At the bottom of the cylinder we see the drive shaft and the Propeller driven by an angular gear.

The engine
It is a horizontal 4-cylinder full-pressure steam engine with circular slide control arranged in a circle on one level. The diameter of the cylinder bores is 18 mm. Unfortunately, I do not know the size of the piston stroke. The pistons of the 4 single-acting cylinders transfer their power to the vertically arranged crankshaft via a common crank pin. One level above is the controlling common cam of the circular slide.

In Figure 6, the construction of the crankshaft is clearly visible in the center of the image. A cylinder unit with a steam line can be seen on the left, with the lubricating nipple for the crankshaft bearing in the middle in the foreground. There are two ring lines for supply and exhaust steam. With a reversing slide, they can alternately direct live steam or exhaust steam.

The slider is operated from the outside by a lever. One of the lines can be seen in picture 6 at the top of the picture. Figure 7 shows the feed water pump. By flipping the toggle on the front of the pump, the plunger can be moved by hand to fill the kettle with water. With the engine running, the toggle is then put back and the pump piston is driven by the crankshaft via an eccentric. The flow rate can be set using the knurled wheel, which is clearly visible in Figure 7.

The boiler
The importance of the feedwater pump for operation becomes apparent when looking at the boiler design. Like the model steam boilers mentioned above, it is a continuous flow boiler. Once-through boilers – called DuK for short – have been around since the middle of the 19th century. Around 1920 they began to be used industrially (Benson boilers, Sulzer boilers). With the same steam output, these boilers have a lower weight and volume than conventional boilers. So actually this form is ideal for the outboard motor because space is a problem. One issue is that they have to be constantly fed due to the principle explained below. In simple terms, the DuK consists of a tube that is open on both sides and heated on the outside (Fig. 9). Water is constantly pumped in at one end, which is heated up until it evaporates as it passes through the pipe system and exits as steam at the other end. Although it was possible to achieve high pressures and steam volumes with a comparatively small size in really large systems, operating a DuK in a model is not easy. Steam can only be generated when the steam engine is running and driving the feed pump. If the machine is stationary, no water is pumped and therefore no steam is generated, which is why the machine does not start again. Since the driving model cannot be pumped up by hand, an electrical solution had to be found by Mr. Carlberg for his outboard engine.

Coming back to our topic - the feed water pump can be switched to manual operation for precisely this reason. You also have to pump hard before heating up to fill the pipe completely with water. It is a difficult undertaking, as I was able to experience. The necessary water is taken directly from the lake via a hose and conveyed by the pump into the ascending pipe spiral, which is located in the sheet metal cylinder above the engine room. In picture 5 this is very clearly visible. The steam is extracted from the upper end of the pipe and sent back down through a steam pipe and fed to the machine.

For some incomprehensible reasons, this pipe is outside the furnace (no reheater) and not insulated (undesirable heat loss)! The exhaust steam from the machine passes through a condensate separator (which often must be emptied) and the residual steam is routed through the chimney. The keen, steam experienced reader will immediately recognize potential for improvement in the construction, especially with regard to the energy balance. Of course, the steam outboard has the necessary safety devices, but they did not give me the necessary feeling of security when operating the system. I particularly liked the pointer on the pressure gauge. It stands immovably on the scale end value of 15 bar (Last photo). According to the operating instructions, 9 bar pressure should be sufficient to operate the system, but this could not be checked due to the lack of a working pressure gauge.

Figure 9 shows the spring-loaded safety valve which - if it works at all - is set to the last notch, i.e. set to the highest pressure.

The firing
You do not need much to fire the cauldron: grill lighter, wood shavings, poker, matches and work gloves. All of this is available everywhere in Sweden, which makes operation easy and possible at any time. The fire burns inside the ascending spiral tube. At the upper end of the tin cylinder there is a firing flap through which the heating material is poured into the furnace. The combustion residues fall through a grate into an ash drawer at the bottom of the boiler and can be easily removed. Like every steam engine, this one also has a lubricating device. For this purpose, there is a cylinder oil press on the outside of the housing (Fig. 10).

The crankshaft exits the housing vertically downwards and drives the propeller directly via a shaft and an angular gear. The shaft runs in a tube that is firmly connected to the gearbox housing. By rotating the tube in its longitudinal axis, the propeller is pivoted in a different direction and the direction of travel is changed. The lever provided for this can be seen in Figure 3 below the metal cylinder on the left-hand side. Unlike other well-known outboards the "motor" itself cannot be pivoted, but is firmly connected to the motor mount of the boat.

I really enjoyed exploring and operating this somewhat quirky power unit. The machine has now been given its well-deserved retirement and is on display at Forsvik Industrial Museum. Thanks to Sven Olof Carlberg for building it!