"三人划的小艇" can be translated into English as "a small boat rowed by three people" or more specifically, depending on the context, "a three-person rowing boat" or "a dinghy for three rowers".
"A small boat rowed by three people" clearly describes the boat and the number of rowers.
"A three-person rowing boat" is a more concise and commonly used term in contexts related to boating or rowing sports.
"A dinghy for three rowers" specifies the type of boat (dinghy) and its capacity for rowers.
Choose the phrase that best fits your specific context.