I may be wrong (usually am), but isn't it just the luck of the draw as to which person of the cloth is onboard and then they usually do a non demoninational service that everyone can attend !
When I am cruising I always go the service and it has been a different religous representation at each service but it is structured as such that everyone can join in..As a matter of fact I have enjoyed them and especially like that it takes less then 30 minutes