Thank you, now I understand better.
So when on an oil rig the Cat A take off stops the helicopter from touching the sea in case one engine fails because it has more height?
The videos I have seen make it look hard for a helicopter to land back on a rig helipad as soon as it moves forward because there seems to be very little sight of the pad.
In the video below what is happening in the hover before they go up?
Also, if one engine stops at around 38 secs in the video I don't think they can land again on the pad can they? How will they see clearly what they are doing?