頁籤選單縮合
題 名 | 拖網漁具基礎研究 |
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作 者 | 李燦然; | 書刊名 | 中華農學會報 |
卷 期 | 76 1971.12[民60.12] |
頁 次 | 頁120-122 |
關鍵詞 | 拖網漁具; |
語 文 | 中文(Chinese) |
中文摘要 | 當拖網漁船於漁場進行拖網作業時,由於網具規模很大,長達數十或數百公尺,作業深度由數十至數百公尺不等,加上海底地形、地質、流水等多項變化因素,故欲確實瞭解瞬息萬變的拖網漁具,在作業中實際情況是非常困難。雖然人可潛入水中,直接觀察曳行中之網具形態,但仍因能見度之有限,而難以窺得全貌。目前雖然已有許多新穎網具測定儀器,如廣角魚?探知機,水中聲納,網位測定器,網高測定器,張力計等等,仍然以斷章取義的方法,概略地估計網具之全部作業情況,若以設備完善之水中潛艇,或全套水中電視監視系統來協助觀測,則因經費上又將過度龐大。故一般漁具之研究者,皆認為以各部份之觀測值,以適當之模型加以試驗,作成假說,再比較實際值與試驗間的關係,然後應用此關係值,來推論網具於各種情況下之變化。故作者為了以最有效,且最經濟的方法,來瞭解我國目前的拖網漁具之水中作業狀況,其所受之流體抵抗,及漁獲效率等,著手實行一系列之模型實驗,且尋求實際網地與模型網地間的關係,進一步檢討目前托網網具要提高漁獲效率,而應作之漁具設計改進事項。 將我國目前所使用之拖網漁具分別作成模型實驗,計有A、B、C、D、E等五型,其使用之模型網具分別為實際網具大小之1/20,1/20,1/20,1/72,1/20。而A、E、C 3型所用之No. 2 網材料為保利艾基(Polyethylene)網線,而其手木則分別為5.2公分(A型),與12.5公分(C、E型),實驗B是為了瞭解於使用不同高度手木時,網口高度之變化及其流體抵抗之大小。B型模型試驗用No. 3網,材料為尼龍線編成,但手木與縮小比例與模型實驗C,所使用之No. 2 網具相同。係為了瞭解構造相同,網線不同,而產生流水中形狀和抗力等之差異。實驗D所使用之模型為縮尺較小者,乃是為了瞭解模型實驗理論之適用性和其物理特性。此外為了研究網板之展開距離,實驗E,將No. 2網特地加附一對V型網板。 實驗水槽為日本東海區水產研究所船型大水槽,於其設備下,模型網之曳行速度,流體中之抗力皆能自動記錄,且能自水槽上方或兩側拍攝網具之試驗照片。 模型試驗之網具,乃根據田內森三郎博士創立之漁具比較法則而設計。 一般拖網漁具模型所受之流體抵抗均以R=kv?之方程式來檢討,k與n之值隨網具構造和曳行速度而異,於各次試驗中,係數k與指數n,經測定結果各為: RA=0.88V1˙ 33 RB=0.37V1˙ ?? RC=0.71V1˙ ?1 RD=0.0059V1˙ 3? RE=0.36V1˙ ?? 除實驗E中之No. 2網具曾結附網板外,實驗A至D均使用桁木,使網口固定展開。經多次重複試驗得知: 一、網目張開情形:實驗B與實驗C之網目張開情形,較實驗A與D為佳,曳行速度增快後,網目閉塞情形不急據,而當使用愈高之手木時,網地因曳網速度影響較小。 二、網地所受張力之大小:網地所受張力之大小順序是實驗A,實驗B,實驗C,實驗D。於實驗A中,受力最大之處為天井網。網地各部份之受力情形經分析後發現,網地受D之變化與網目之變化相似,僅在袖網與囊網處略有不同,此可能由於網具構造之特性引起。 三、浮子之穩定性:浮子之振動隨曳速增加而變大,實驗C與D之浮子穩定性,較實驗A與B為佳。 四、網具之抗力:當使用相同之手木時,No. 3 網擁有較大之網口高度。實驗E中,測定之拖網抗力約2,520 kg,而實際網地若以理論來估計其抗力,約為2,557.8 kg。 五、網口高度:提高網口高度方法有二,其一為增高手木之高度,及增大網目之大小。其二是於浮子網前方,再加一條前置浮子網,且僅以二條繩索與原先之浮子網連結,不致影響作業程序,但增加其原網口之高度。 六、模型網具縮尺之大小:雖然使用較小比例之縮尺模型,亦可測定網具在水中之大概形狀,但於此實驗中得知,1/20縮尺之模型網具較1/72縮尺之模型網具為詳盡。因此在可能之範圍內,應使用較大之模型實驗為佳。 |
英文摘要 | In order to determine the deformation and resistance of the trawl net used in Taiwan. Model Experiment A, B, C, D and E were carried out in Tokai Regional Fisheries Research Laboratory. In Experiment A, B, C and E, 1/20 model nets were used. Model net No. 2 was woven by polyethylene thread, and employed in Experiments A and C, but each height of danleno employed was of 5.2 cm and 12.5 cm respectively. The purpose of these Experiments were to see the change of the net height and resistance with different height of damlenos. Model net No. 3 employed in Experiment B was made by nylon thread and had 5.2 cm danleno. This experiment gave a comparison with Experiment A in change the shape of net and water flow with the different materials. In Experiment D the net usesd was No. 1 which was made with reduction ratio of 1/72 and material was nylon. This Experiment gave the comparison of different scal model nets in above mentioned mechanical characters. In Experiment E the same model net as in Experiment C was used but operated with the V-door for estimation the spread distance of the V-door and the shape of the trawl gear under towing. The coefficietn of resistance K and an exponent n of v are calculated from the observed data in each experiments A, B, C and D. We have: RA=0.88V1˙ 33 RB=0.37V1˙ ?? RC=0.71V1˙ ?1 RD=0.0059V1˙ 3? In Experiment A the vibration of the net and other changes in the shape are due to the defect construction, having not well proportionated the length of the cod end to the length of the head line. The values of 1h/1t in Experiment B is greater than that of experment A and the height of the square part declined slowly in Experiment B. So the value of n in Experiment approaches 2, which means the projected area of the net mouth to water current and the height of the square part changes a little. As we compare with two Experiments A and C, an obvious fact that the heigher danleno get the effective of the square part and the wedding is employed efficiently to contain the shape of the net, but it should be conpensated with an increase of the tension for each warp under the same towing comditions could be roughly estimated with model net of 1/72 (Experiment D) and of 1/20 (Experiment A, B and C) reduction sizes but the latter gives more detail information. In Experiment E, we have the coefficient of resistance k and the n power as RE=0.36V1˙ ?? In this test, the angle of attack increases beyond 45°, that is not so good for spreading force of the otter boards. During the experiments, the mesh epening of Experiment B and C are better than that the Experiments A and D, and the tension in webbing effected with the velocity A and B are greater than C and D. on the other hand, the stability of the floats of Experiments C and D are better than that of Experiments A and B. |
本系統中英文摘要資訊取自各篇刊載內容。