Captain John Denessen (deceased), a son of Nicholas Denessen, was born in North Brabant, Holland, June 23, 1836. He came to the United States with his parents when but twelve years of age, the mother dying at Buffalo on her way to Little Chute, in, which place the other members of the family reached on sailing vessels. They were among the early pioneers of the Fox River Valley. Captain Denessen resided in that vicinity about fifty years and was actively identified with the boating business for over thirty-five years. It was while living at Little Chute that he first manifested the desire to sail. Soon after the family removed to the Bay Settlement he left home to make his own way in the world. Until about 1858 he steam boated on Green Bay, Fox river and Lake Winnebago, and at this time he married Miss Nettie Denessen Graff and settled permanently at Green Bay. During the Civil war he ran a steam ferry across Fox river at Green Bay, where the Walnut street bridge now stands. After the construction of the bridge he used a skiff as a ferry where the Main street bridge now spans the river. At the same time the Captain owned a small steamer, William Denessen, and also the Annie Denessen, the latter running to DePere. After selling the former to Mr. Van Dyke, he built another steamer, which he named the William Denessen II, both of which he sold. He then built the steamer Arrow, which was larger than either of his other boats, and this too he sold seven years later, the purchasers being parties on Devil's Lake. In the spring of 1882 he built the steamer John Denessen, and in 1889 purchased the steamer Schiller, twenty-two tons, which was lengthened and rechristened the Nettie Denessen. He operated her until his retirement, selling his floating property to four of his sons. Captain Denessen died on Mary 13, 1898, his first wife having preceded him to the future world July 18, 1893. By this union he had nine children: Annie, now the wife of H. Berensen; William ; Joseph; Theodore; Cornelius; Josephine, wife of E. Schwartz; Henry; Mary, wife of L Rondou; and John, Jr. After the death of his first wife he again married, Mrs. Elizabeth Prince becoming his wife, and by this union one child was born. The Captain was a man of sterling integrity and great force of character, and was an honored citizen of Green Bay.

Above taken from the eBook History of the Great Lakes edited by J B Mansfield, pages 1170-1171. Available online at:
https://books.google.com/books?id=s28jAQAAMAAJ&pg=PA1171&lpg=PA1171&dq=nettie+denessen+boat&source=bl&ots=7QyeLk8f01&sig=BFZEIeHZ1lRbRSzh9_E8qSpBTlA&hl=en&sa=X&ved=0ahUKEwin6_vn-d_RAhUl34MKHc0iCKgQ6AEIJDAC#v=onepage&q=nettie%20denessen%20boat&f=false

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Obituary:
Captain Denessen Dead. Word was received from Green Bay on Monday announcing the death of John Denessen, founder of the Denessen steamboat line, which occurred in the Ancient City Sunday night. He had been ill only two days. He came to this country with his parents in 1848 and settled in the town of Preble near Green Bay. In 1870 he built a small ferry boat which he used in ferrying across Fox river, there being at that time no bridge. Later he built the steamers Nettie and John Denessen. Mr. Denessen was one of the oldest settlers in Brown county, and was the oldest steam boat captain on the Fox river and waters of Green Bay. He was 62 years old and leaves a wife and nine children, Mrs. Lizzie Denessen, William, Theodore, Joseph, Henry, Cornelius Jr, Anna, Josephine, and Mary.

From the Advocate of March 19, 1898.

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* Graff has also been spelled DeGreef

Information provided by Find-A-Grave contributor Willemssen #48832678.