Please note that while sailing the centre board is there to minimise leeway. The CB works by creating a low pressure area to the luff of the CB and a high pressure area to the lee of the CB. Because of this the self bailer to the luff will become more efficient with speed whereas bailer to the lee stops functioning all together. If you fit only one bailer it functions only on a tack where it sits to the luff of the CB. If you want your self bailers to work on either tack you have to fit two.
BTW the standard bailer for our class is the Elvstrom/Andersen Supermax. While racing smaller ones are allowed larger ones are not.