RedactedNarrative: The captain and owner of the vessel when he went out with 3 other passengers to tarpon fish around Long Boat Key and Egmont Key.  They began their trip around 0415 on Saturday May 19, 2018.  They began their return to shore around 1700 due to inclement weather approaching the area.  The operator noticed that the vessel began to retain water near the Tropical Shores neighborhood on the west side of Tampa Bay.  Within seconds of noticing the water coming onboard, the vessel began to capsize and eventually sank sending all 4 passengers into the water.  All 4 men treaded water for about 45 minutes until a good samaritan rescued them and pulled them from the water.  Coast Guard retrieved the men and brought them to their station where myself and an Officer interviewed the passengers to figure out the cause of the accident.   The operator stated that he had a local mechanic replace his bilge pump and wiring 3 weeks prior to the accident.  He stated that the bilge was working fine on previous fishing trips.  The cause of the accident is due to a faulty bilge system.  The operator believes the failure was due to a loose fitting in the bilge.  The operator also stated that they did not strike any submerged objects during the course of the day.