Domestic hot water and heating

[Jd1]

I am trying to figure out the heating system in a relatively new to me Catalina Mk2. I have a Webasto auxiliary diesel heater (TSL-17) , a Seaward S600 domestic hot water tank and a 35 hp Universal engine.
I was under the impression that hot water and heat could be generated by the engine coolant, the auxiliary diesel heater and of course the electric heater in the Seaward unit.
I have made some progress in figuring things out but I am still far short of understanding the system and thought that maybe somebody here could give me a pointer or three.
I think I am ok in understanding the Webasto portion of the system. There is a breaker marked 'heater' on the main panel which enables a circulation pump and the Webasto, there is a thermostat which turns on the fans for all the hot water to air heat exchangers throughout the boat and there is a three position switch that has 'engine heat' on one side and 'system heat' on the other side. Mid position is probably 'off'.
Besides needing to understand all systems and how they work, at this point I am baffled by the 'engine heat' portion of the system. I believe that the heating system works fine but there seems to be no heat diverted to the domestic hot water unit (the Seaward). Since I don't know what I should or should not expect to see, my next step in trying to work things out will be to trace all the hot water lines in the boat.

This brings us to the reason for this post ..... I am wondering how heat is transfered from the engine to the other systems (cabin heaters and domestic hot water heater). Is there an accepted way of doing this or are different methods used? I would expect to have the engine coolant go through a heat exchanger to the Webasto hot water loop but so far I have not been able to figure out exactly what is happening.
Part of my difficulty seems to be the fact that the engine produces little heat at idle tied to the dock. Today for example I ran the engine for 45 minutes trying to find a pesky coolant/antifreeze leak (without luck) .... at the end of the 45 minutes I had some warm air coming from the heater outlets but the domestic hot water was stone cold. I will try to do this test again under real conditions on the water but any hints as to what I should see with this system would be appreciated.
.... so far I haven't even been able to find the heating loop connections for the Seaward. This shouldn't be rocket science but I am really starting to wonder.

[Jd1]

I got myself well worked up over the whole issue but thanks to the venting I did, I approached things from a new angle today. Net result, I found the engine heat exchanger in the port floor compartment under the rear berth. I had looked in there before but didn't look thorough enough - it was tucked under fiberglass, away from the compartment cover.
Even though I didn't trace all hot water lines, everything is starting to make sense. I suspect that my issue might be a mis-adjusted bypass valve for the hot water heater and I will fine tune that before worrying about anything else for now.

[GordMay]

Well done, JD.

[DeepFrz]

Yes the best thing to do when you have a new system is to trace it all out. Then put it down on paper so you can make sense of the whole thing. You might want to start a binder for all your different systems. Plasticoating your pages helps keep them in good shape over the years.