You do need sail numbers for both cruisers and dinghies. If you don't have a sail number please apply to the ISA.
Usually they are expensive but in Courtown Sailing Club we keep our prices as low as possible. Under the regulations of the ISA a senior powerboat instructor in a powerboat school can give the course and the ratio is 1 to 3.
All the instructors are fully qualified according to the standards of the ISA.