Cat A Part A?
Helibuoy,
The WAT Graph is only relevant for the climb segment above 200 feet and should not affect your Deck Operating weight.
Compare the graphs for the 3D, 3DE & 3DF engines on the EP - the WAT figures vary but the 2 and a half minute OEI parameter is the same for all 3 variants and this is the parameter used for segments 1 and segment 2 of the profile. Segment 3 (200 feet to 1000 feet) relies on the Max Continuous OEI for the 3D and the 30 minute OEI for the 3DE & 3DF which is why the WAT graphs differ.
For Offshore Ops most Operators use Twin Engine Hover out of Ground Effect (HOGE) graphs to calculate Landing and take-off Mass although the profile flown is similar if not identical to Cat A Part A.
We comply with Performance Class 2 and this is perfectly acceptable to all the Major Oil Companies that I have come across.
2 Engine HOGE for Unrestricted Decks (fully compliant with CAP437/ICAO Annex 14) gives the following figures:
For a basic 412 or 412SP with C Box Torque indication only your MTOM at 30 Deg C is 11400lbs.
For the 412HP or 412EP with Mast Torque indication your MTOM is 11900 at 30 Deg C.
For restricted decks - i.e. not fully compliant due to a whole range of factors we use HOGE minus 500 lbs to give extra power in hand.
Hope this is of some use.
Trog