Simon.
Group exhaust valve coolingwater pipes.
To make an understandable drawing of this system is not easy, so when keeping an eye on the confusing drawing below I`ll try to give an explanation:
making use of the systemdrawing and copy the system would not work so basis for the described system is photos and common engineering sense.
The main coolingwater outlet from the dieselengine is close to where the manifold endflange joins the transition piece flange. The pipe goes down to the main coolingwater valve at the aft bulkhead, to the short pipe between the main cooling watervalve and the main seavalve and then via the main seavalve to the group exhaust valve and overboard.
Immediately after the exhaust manifold it is a small pipe branch off which take some of the coolingwater to the lower part of the transition flange, the water leaves the same flange at the outlet on the top. Then the water goes to the lower inlet of the endflange and leaves same at the outlet on the top. It goes down and join the short pipe between the main coolingwater valve and the main sea ( overboard) valve. On the short pipe between the two mainvalves is a branch off to a two way cock, this cock can be put in drain position leading the system to a funnel and bilge or to the other position connecting the system the the other engine system.
The main drain pipe (yellow)and valve is obvious and ends together with other drains in a funnel to the bilge.
Allthough not shown on one of the engines, there should be a manometer connection to the main drain of the group exhaust valve, that drain comes from the space between the group exhaustvalve and mufflervalve which might have a severe leakage and full seapressure in the space.
The system is based on interpretation of photos and some basic musts but in the end an assumption from me.
Tore