An SR22 pilot reported rejecting the takeoff at rotation speed when the passenger door is detected to be ajar. Braking on the wet runway was ineffective and the aircraft went into the grass overrun before stopping without damage.

Narrative

During take-off roll; the right entry door was detected to be not secure. This is a published abnormality whereby a take-off abort is called for if practical. The abort was initiated at rotation speed with 3;000 FT remaining. Three thousand FT is more than twice the published required ground roll landing distance for the conditions. Moderate braking was applied with little effect. Maximum braking was applied and the aircraft began to slow; yet acted as if it was on ice. The runway was wet due to recent rain; but there was no standing water. The main wheels had to be hydroplaning during the brake application. At the runway end; the aircraft was still in forward motion and departed the pavement for the wet grass overrun. The overrun was level for approximately 200 FT and then descends abruptly for approximately 200 more FT. At the end of the overrun is a perimeter fence. The aircraft was almost stopped at the end of the level overrun; but at what can only be described as surreal slow motion; it continued down the hill in the direction of the fence. Brakes were still forcefully applied throughout. The aircraft finally came to a full stop some 30 FT short of the fence. There was no damage to the aircraft; no injuries to any person; and no damage to any airport property.