RedactedNarrative: While operator was intermittently fishing for about an hour and a half, vessel sank and came to rest on bottom in 4 feet of water, submerging engines and most of the cockpit.   After vessel was recovered, inspection revealed a through hull fitting just above the waterline near the stern on the starboard side that was open to the bilge. The plastic hose going to it was crumbling and had only a small section remaining.  Automatic bilge pump feature appeared inoperative.  Operator indicated bilge plug stayed in hull while boat stayed on the lift for the past several years.  Rainwater had likely filled the bilge while on the lift, and the extra weight contributed to the hull fitting taking on water from the time he got underway (unknown to the operator).