How did longship oarsmen coordinate their efforts?

Simple: By watching the man in front of you, or if in the stern the man next to you. It get's messy if you mistime a stroke, many insults thrown. There are many videos on youTube if you require proof. read more

usuallly by drum I believe. This was a solution that was developed independantly my many seafaring nations. It was easy to hear, worked in bad weather and didn't require someone to loose their voice by shouting "pull" for hours at a time. read more

According to Aurane the Ironborn longships are equal to their war galley, ''Lord Balon’s Great Kraken and the warships of the Iron Fleet were made for battle, not for raids. They are the equal of our lesser war galleys in speed and strength, and most are better crewed and captained. read more