Thanks all for the reply. Met the owner of the 3587 and found out that the boat was gas propelled. It appears that BayLiner equipped gas fueled vessels with this device. They offered the diesel boats a option of a 6” dia straight outlet. I found a bronze exhaust vent at 7” size the source being NZ. The one on the 3587 is 8.5” x9.25 with a 7.5” mouth with a 5” ID and 5.5” OD However this device will reduce the station wagon affect by forcing the exhaust flow into the chine stream.