We have to do something with the exhaust from the engine. As it leaves the engine it will be a mixture of water, steam and emulsified oil from the cylinder lubrication. At one time this would have been dumped over the side into the lake and forgotten. In my recollection it did no harm but in these pollution-conscious days when even steam from cooling towers is seen to be pollution we must do much better. In fact we can put the exhaust to good use to induce a draught in the chimney to improve combustion and to improve the image of the boat in action.
The price we pay is to have two separating tanks in the boat. Figure 34 is of my paddle driven boat. The two black tanks are the separators. The engine exhausts through the soft pipe on its left into the upper tank in the picture. There the oil is separated and most of the water. The exhaust then flows through the pipe from the top of the separator across the boat into the second separator where any residual oil is trapped and some steam condenses. The exhaust leaves from the top of the second separator to go through the insulated pipe to go to the base of the chimney. There it is directed upwards to induce a flow through the boiler. The fitting is shown in figure 35. It is located in the chimney by the two spiders. Note the slotted tube joining the main pipe to the extension to vent off any oil or water that gets this far. No water is discharged upwards to fall back on to the boat or into the lake and it is possible to hear the increased note of the burner when the engine is running at high speed and. It is very satisfactory.
On a safety note, water in long tanks can easily slosh forwards should the boat be stopped suddenly or pushed from the bank. It is too easy to have a sudden spurt of scalding hot water from the chimney if the tanks do not have baffles and have their outlets in the middle at the top. I have no experience with vertical separators.