A heavyish offshore machine will be around 8000 lb with two pilots, so if you assume no life jackets, liferafts or ADELT then you are probably down to around 7800 lb or even less if single pilot. At seal level and ISA + 15°C you still have 11,700 lb RTOM for CAT A, so with the fuel figure quoted above that gives a payload of at least 2300 lb and more like 2500 lb+.