農業部-水產試驗所全球資訊網農業部-水產試驗所全球資訊網

綠島附近海域因有黑潮主軸流經，表層海水含豐富的營養鹽，高經濟價值魚類的大量群聚，而為台灣沿岸海域的重要漁場之一。經研究調查結果發現，在黑潮流速為2.8海哩/小時的基礎下，當繫纜繩與水平線之角度成30度時，其位於錨碇處繫纜索之垂直張力與水平拉力分別為2,600 lb及 4,470 lb，繫纜索本身的拉力則為 5,571 lb，即約為2,350 kg (2.35 ton)，然而，本研究所使用的繫纜索 (=90 mm) 之破斷力保守估計約為 78.83 ton，遠大於繫纜索本身的拉力。造成人工浮魚礁漂(移)流的因素很多，且大致可歸納以下幾個原因：(1)、人工浮魚礁之繫纜索與海底岩石的長期磨擦而斷裂，(2)、在正常的情況下，鐵鍊於海水中的腐蝕率為 1.0 公厘/年，其最大值可達每年 2.0-3.0公厘者，但本研究所使用的鐵鍊直徑卻高達 38.0 公厘，因此，於一年內使鐵鍊完全腐蝕似乎不太可能，(3)、表層海水的運動，導致繫纜索與鐵鍊連接處或繫纜索或鐵鍊自身因水流運動與張力作用所造成的長期彎曲變形而斷裂，(4)、經由繫纜索斷裂處推測，似乎以人為的外力因素導致繫纜索斷裂的成份較高。

The main purpose of this study was to realize the drag force on the anchor and the tension of the mooring lines against the Kuroshio current with its velocity of 2.8 knots. Based on the static analysis of the mooring lines on deployed fish aggregating devices (FADs) at the depth of 440 meters with velocity of 2.8 knots of the Kuroshio current, the drag force on the device is 2,250 lb. With the angle of the mooring line against the horizontal at 30o, the tension of the anchor and of the device were 2,600 lb and 4,470 lb, respectively. Therefore, the drag force of the polypropylene synthetic ropes was calculated as 5,571 lb (2.35 tons) which is much lower than the breaking strength 78.93 tons of the rope. The drifting of the device may be attributed to the broken-end of the polypropylene rope with a very smooth incision, which might have been cut by a sharp axe.
Key words: Deployed fish aggregating devices, Mooring lines, Mechanical analysis, Green Island