It might be easier to have it external. Unlike the main and (roller-furled)
jib, the
spinnaker is detached from the halyard each time it is used, hence the chance to lose it inside the mast is greater than is the case with other halyards. It's also easier to play around with it when it's external. Occasionally the sheet and guy can get loose at the same time and the
spinnaker can get caught up in your shrouds or wrapped around your forestay, or foredeck crew...and it helps to be able to loosen the whole mess...