Complex sentence: Ragnall and Sihtric were active in Ireland in 917, leading separate fleets, Ragnall occupying Waterford for a period and raiding Munster from it along with his friend or deputy Ottir Iarla.
Split into simpler sentences: Ragnall and Sihtric were active in Ireland in 917, leading separate fleets. Ragnall occupied Waterford for a period and raided Munster from it along with his friend or deputy Ottir Iarla.