There are no scheduled flights or ferries to the Dahlak Islands. The archipelago is a national park, and the only way in is on a chartered boat from Massawa, the Eritrean port across the strait. You cannot turn up at the harbour and hire one yourself — boats need a permit from the Ministry of Tourism, which is arranged through one of the licensed agencies in Asmara or Massawa.
The crossing to Dahlak Kebir takes three to four hours in a slow motor boat, faster on one of the dive yachts. Most trips run as live-aboards of three to seven nights, sleeping on deck or in basic cabins. Diving operations have been intermittent — Eritrea opens and closes to outsiders without warning, and the few outfits that work the islands change from year to year. Confirm before flying in.
The sea is at its calmest from October to April. Between June and September the southwest monsoon kicks up swell and visibility drops; few boats run.