Hi Dek,
I have a 2007 Bavaria 30 with a Volvo D1-20 (18HP) engine, I would imagne they are similar regarding fuel consumption.
At cruising speed, 5kts (approx 2300 rpm), we get about 1.5l per hour. Its never any more than that and could be slightly less but for passage planning I always use 1.5l/hr and it seems to reflect consumption accurately enough across a broad range of sea state and wind we encounter.
Hope that helps.
John