The pilot had operated from the 750 metre strip many times, usually in a Britten-Norman Islander BN-2 aircraft. On this occasion, however, the BN-2 was not available so a PA23 aircraft was used. The strip was firm and covered with grass 10-15 cm long. There had been intermittent showers on the strip for some hours. Although the pilot had operated PA23 aircraft from the strip previously, he had not done so in wet conditions. The pilot held the aircraft on the brakes and set full power before beginning the takeoff roll with 10` flap selected. He reported being concerned part way along the strip at what appeared a slow rate of acceleration but put this down to the different characteristics of the PA23 aircraft compared to the BN-2. Further down the strip the pilot considered aborting the takeoff but decided to continue after concluding that there was insufficient strip remaining for the aircraft to be stopped. The aircraft became airborne about 20 metres from the upwind end of the strip and the left wing contacted vegetation a short distance further on. This slewed the aircraft left, resulting in the fuselage being broken just aft of the cockpit as the aircraft slowed and came to rest in mangroves. The takeoff performance chart for the aircraft indicated that the strip was of sufficient length for take-off under dry conditions. However, there was no information available to the pilot as to what allowance should be made for long wet grass conditions. In the event, the aircraft became airborne near the end of the strip, probably before the correct speed had been reached. This accident was not the subject of an on-site investigation and this report is based on information provided by the pilot.