I took the ferry to Washington Island in Door County, WI about 28 years ago. Their ferry's are a bit smaller than the one in your pic. They had a MH on it's sister ferry coming back from the island, but they had the MH loaded on "properly," along with another half dozen cars. The scary thing was there were about 4-5 ft waves and that ferry was porpoise'ing like mad. We were on the other ferry going the other direction when we passed them, equally porpoise'ing. My wife was about 5 months pregnant. She was not a happy boater, if you know what I mean!
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