It seems that the polynesians were skilled seafarers. You'd think they would have to be to travel across oceans in canoes they carved to maintain their strength despite the ocean winds and waves.The exact time that the Hawaiians arrived in Hawai`i is still a mystery. Some would say that they arrived around the 3rd century from the Marquesas and were followed by Tahitian settlers in 1300 AD who conquered the original inhabitants. Others believe that there was only a single, extended period of settlement.
There is substantial archaeological as well as paleoecological evidence confirming Hawaiian settlement no later than the year 800, and quite possibly as early as the years 300–500. The immediate source of the colonizing population in Hawai'i is likely to have been the Southern Marquesas, but continued contact between Hawai'i and islands in the core region is indicated by linguistic evidence, abundant oral traditions, botanical indications, uniquely shared DNA sequences in populations of the Pacific Rat, and possibly some archaeological style changes as well. However, long-distance voyaging between Hawai'i and the central Eastern Polynesian core became less frequent after about AD 1200, and was little more than a memory encoded in Hawaiian oral traditions by the time of European contact.
The only evidence for a Tahitian conquest of the islands are the legends of Hawaiʻiloa and the navigator-priest Paʻao, who is said to have made a voyage between Hawaiʻi and the island of "Kahiki" (Tahiti) and introduced many new customs. Some Hawaiians believe that there was a real historical Pa'ao.
King Kalakaua in his book, The Legends and Myths of Hawaii, claims that Paao was from Samoa. The religion he brought, the Kahuna religion was from Samoa. Paao was instrumental in bringing the High Chief Pili from Samoa to rule the island of Hawaii. Pili is a well known entity in Samoan mythology. His descendents were one of the highest ranked families in Samoa even to this day. According to the geneology laid out by King Kalakaua, King Kamehameha was also a descendant of Pili. The big island of Savaii in the Samoan archipeligo was known as Hawaiki in ancient times.
Some writers believe that there were other settlers in Hawai'i, peoples who were forced back into remote valleys by newer arrivals. They claim that stories about menehune, little people who built heiaus and fishponds, prove the existence of ancient peoples who settled the islands before the Hawaiians.
There is one puzzling artifact on the island of Kauaʻi, one that has never been satisfactorily explained. Running alongside the Waimea River is an ancient aqueduct known as the "Menehune ditch." This channel once brought water from the Waimea River to irrigate taro fields. The rocks were shaped into rectangular bricks and carefully fitted together — a method of stonework requiring immense labor, and not typical of Hawaiian rockwork. This ditch is currently believed to have been constructed before Captain Cook's first visit.