If you follow the arrows you can see that this HX is broken into quarters and is a four pass HX. Raw water enters & then flows to the opposite end, returns to the inlet end, turns and heads back to the opposite end and finally turns back towards the inlet end and finally gets ejected into the wet exhaust system.


If you click on the picture to blow it up you'll notice a chunk of an impeller blade that took up residence in the heat exchanger.