With the A++ and C+, as well as the 412, there is no need to ditch if OEI, you can land on a platform. In the GOM, the alternate can be either a designated platform or an airport on land, depending on the situation. When you're going 150NM+ one way outbound, it gets difficult to use onshore alternates with any reasonable payload. The S92s use an onshore alternate all the time, due to customer requirements.