I have a Garmin 750S chart plotter/fish finder which will connect to a NMEA 2000 system. This enables you to input various information into the Garmin or other brand NMEA 2000 compliant unit, Your Raymarine unit should accept the input from a NMEA 2000 system.
Maretron manufacture an analogue engine monitoring system which has a wiring harness to connect straight into the Yanmar 3MY30 engine. The unit is EMS100 and the wiring harness is EMSYMR01. You also need some NMEA 2000 cable and fittings to connect the EMS100 to, in my case the Garmin 750, or whatever display unit you have.
There are many different lots of information you can feed into your display, oil pressure, cooling water temperature, and with the correct sensing units fuel flow, fuel tank level, water tank levels, even ocean/river water temperature etc. Maretron also make a small display if you want to have a separate display other than your chart display unit.
If you go to :-
http://www.maretron.com/products/pdf/EM ... _Sheet.pdf (this is the data sheet)
or
http://www.maretron.com/support/manuals ... UM_1.0.pdf (this is the manual)
You will find more information on the equipment. There is also a list of the Yanmar engines which the unit suits. You can add to the system later if you want other data displayed.
In Australia where I am, the cost for the EMS100 and Harness is about $Aus1100 plus the NMEA cabling and fittings.
It maybe a lot cheaper in the US, for many things we seem to pay a premium over here.
Geoff