// assume you bind a list of persons to the ComboBox with 'Name' as DisplayMember:
            suggestComboBox1.DataSource = DB.GetAllBoats();
            suggestComboBox1.DisplayMember = "Manufacturer";

            // then you have to set the PropertySelector like this:
            suggestComboBox1.PropertySelector = (collection => collection.Cast<Boat>().Select(p => p.Manufacturer).Distinct());