@article{oai:ir.kagoshima-u.ac.jp:00010884,
 author = {源河, 朝之},
 issue = {2},
 journal = {鹿児島大学水産学部紀要=Memoirs of Faculty of Fisheries Kagoshima University},
 month = {2016-10-31},
 note = {On the occasion of operation and work of the fishing-vessels, important instruments of
the magnetic-compass equipped on the purpose of decision of a way, setting direction of
fishing gear or confirmation of operation-location. There are two kinds of compass, one is
the magnetic-compass, and another is the gyrocompass. As to the fishing-vessels of our
country, almost vessels not exceeding 100 tons equipped only the magnetic-compass and
operates, but large vessels takes the gyro-compasss with the magnetic-compass.
Generally, as compared with the magnetic-compass, the gyro-compass has not the appearance of deviation,
so that its degree of confidence is higher. But, while, there are
many cases when it is not fit for small vessels, for we need techniques of conservation
and an accident mending, high knowledge and techniques of electricity or machine.
On the other hand, according to a White Paper of the Maritime Safety Agency, it
became cleared that the magnetic-compass was low-priced, and that had not afraid of accident,
conservation, and there was merit that anyone was able to use easily but there were many
question points on the deviation above-mentioned, so that had some connections with many
maritime accidents.
On the primary factor of appearance of the magnetic-compass-deviation, the investigation and countermeasure have been studied until new,
but it is not all enough.
Therefore, the present writer devided the generation factor of deviation into the primary
factor of internal and external, the former is i. e. of generation factor of the deviation due
to influence of the hull-magnetism and the latter is a primary factor of alternation due to
the locality-magnetism-field, i. e. influence of the local-attraction and the solar eclipse,
extraordinary generation of sun-spot, and made a measurement many times.
The method of study and results is as follows.
The present writer mainly measured the deviation by means of bearing of a distant
terrestrial object, calculated the deviation-co-efficient and analyzed the hull-magnetism-components.
First of all, examined a primary factor of internal on a primary factor of the magnetic-compass-deviation.
Recent times, from the old-system-construction-method, the construction-method of fishing-vessels improved to the block-system-construction and the construction-method from
rivetting system turned into electric welding-method, and made a rapid progress, but the
actual state of the hull-magnetism of construction-process accompained with the rapid progress was complicated,
so that the analysis and compensation on the generation-deviation
became more difficult., So, from 1951 to 1969, in order to these investigations, the materials got from test
ships, a fisheries experiment Station, Kagoshima prefecture,and deviation-compensation-materials of construction-vessels, Mukozima Factory of Hitachi-ship-building-institutes, Onomichi add to the experimental-materials with fishing-vessels (six vessels), the Faculty of
Fisheries, Kagoshima University, and analyzed, investigated. That is to say, as compared with the
actual state of the hull-magnetism of fishing-vessels by means of new and old-construction-method, it was evidence that new-construction-method was more remarkably about the yearly fluctuation of the deviation-change, and that
especially after construction was remarkably, and the compensation was recognized to be
difficult. It is confirmed due to existence of the sub-permanent-magnetism, prosperity and
decay.
Besides, the present writer stated that complete compensation and certification of stability of deviation should be done by measurement of the permanent-magnetism at the
magnetic-equator, and it is confirmed that it took 1-3 years until the stabilization.
It was ascertained that a method contrary to former was adapted for many vessels, on
the correction of heeling error.
Judging from the results of wooden-vessels and composit vessel, it unexpectedly approved of a great deal of the deviation-generation, and it is confirmed that it took about six
months unil the stabilization., This may be due to the narrowness of the bridge and increase of rigging.
It was ascertained that judging formula tan. θ=C/B which depends on the hull-permanent-magnetism was not fit to the new-construction-method.
This may be due to difference of the construction-direction under the block construction
respectively.
Also, judging from the results of the material-investigation, it generally proved that
magnetization was greater than magnetization of under rigging.
This may be due to difference of polarity of the magnetization respectively, and complexity of rigging,
and it was ascertained that induced-magnetism-components increased on
the construction-vessels of the New-method. Next, on the primary factor of external, first of all, the measurements of the local-attraction in the circumference of Kagoshima-bay and the Lake Ikeda were carried out from
1960 to 1967, and were ascertained the existence of considerable the local-attraction, and
then the existence of the local-attraction at the entrance of Kagoshima-bay was found to be along in the side of the Satsuma peninsula, and the maximum value obtained in the
measuring was 2.5°W. This may be assumed due to the existence of iron-sand, deposits
and volcanic chain etc., Next, also the measurements of the local-attraction on surrounding of Sakurazima were
carried out and the existence of the local-attraction was ascertained, but on the actual
state, polarity was found to be quite antagonistic, in the center of Sakurazima, the local-attraction on the northern-seaside of Sakurazima and on the southern-seaside of Sakurazima.
And the maximum value obtained in the measuring was 4.2°W in the north sie, and 3.8°E
in the south side, respectively.
The 'local-attraction' was assumed to be owing its origih to the residual therm magnetism of the lava issued at the volcanic eruption of the islet Sakurazima.
The measurements of the local-attraction in the circumference of out-of-bay were ascertained, and assumed this may be due to the existence of iron-sand, mineral deposits, and
mine on land.
Also, the local-attraction in the circumference of the Lake Ikeda was existend and
polarity was found to be antagonistic, in the north side and in the south side at lake, i. e.
the magnetizing was E,ly in the northern side of the circumference of the lake Ikeda, while
it was W,ly in the southern side, the maximum value obtained 2.3°W. This may be due to
the existence of the mines, deposits and iron-sand. Next, on the influence of the extraordinary astronomy phenomenon upon the magnetic-compass-deviation, made an observation
of the annular eclipse at Takara island of Tokara chain of islands, Kagoshima prefecture
on April 19th 1958 and the deviation-change of about, 1° though a little was recognized.
Again, when the extaordinary generation of the sun-spot, made an observation of alternation of the compass-needle in laboratory room, and some alternations, showed the maximum
width 0.4°. This may be due to the generation of magnetic-storm and other causes and
soon, but it will be necessary to have farther investigations. The summary of results for
investigation is described as follows., 1) The block-system-construction-method have large sub-permanent-magnetism-components,
as compared with the old-construction-method, genrally after construction, the
deviation fluctuated large. So, it took about 1-3 years until the stabilization of the hull-magnetism.
2) It was ascertained that the induction-magnetic-components of the latest construcsion-vessels had large comparatively.
3) Judgement formula of construction-direction which used co-efficient (B), (C) issued
at the hull-permanent-magnetism, i. e. tan. θ=C/B was not fit to the new-construction-method.
4) On the correction of heeling error of the block-construction-vessels, a reverse compensation-method opposite the conventional theory applied for many vessels.
5) Generally magnetization under equipping was larger than magnetization on the
building ship.
6) The sub-permanent-magnetism reduced gradually, and the hull-permanent-magnetism
was stabilized, but the certification will be necessary to make an observation at the magnetic-equator.
7) The latest wooden-vessels have a tendency to appear large unexpectedly, so that it
was ascertained that composite vessel had to manage in the same way as steel vessel.
Also, the sub-permanent-magnetism was recognized to some extent, but it took six months and it did not take so the time as steel vessel. 8) Fluctuation of the geo-magnetism due to the local-attraction was large considerably.
So that it was necessary to pay attention for considerable deviation on the magnetic-compass of the ship's voyage arised.
9) On extraordinary-astronomy-phenomenon, i. e. the annular eclipse, the solarr eclipse,
and the generation of the sun-spot etc, had an effect upon the magnetic-compass. But it
has almost no disturbing influence on the ship's voyage., 船舶に装備するコンパスには,磁気コンパスとジャイロコンパスとがあるが,漁船(大型船は別として)には主として磁気コンパスが使用されている。これは漁船の針路の決定,漁場の確認,投網,投縄等の漁具の設定に欠くことのできない計器である。コンパスは誤差が極めて小さいことが望ましい。磁気コンパスの誤差を自差というが,その発生は地球磁場中で,船体構成材料,漁撈機械等の帯磁と,それらの設置,または運用によって,特別に船内磁場が形成されるからである。したがって,その実態を究明し,それに対する対策を確立するために本研究をおこなったが,その要点は次のようなものである。
第1章 船体帯磁測定法の吟味
船体帯磁を測定するにあたり,磁場測定器による方法と,自差測定によって自差係数を算出し,船体帯磁を解析する方法のうち,後者が,実用的で,かつ,測定技術も簡単であることから採用した。, 第2章 構成法と構成材料別による船体帯磁と自差
船体建造に際し,その帯磁は構成材料によってそれぞれ異なった特性を示し,それが自差に影響をおよぼすことの大要を述べた。
(1) 木造船も,木鉄交造船となる傾向にあり,その帯磁はブロック式に準じた傾向がみられ,その安定には鋼船に比べ短期間の約半年を要することが確かめられた。
(2) 木造船には,従来,自差を生ずる要因が極めて小さいと考えられていたが,実際に大きな自差が発生することを認め,その成因についても論及した。
(3) 小型漁船に装備したレーダーは,磁気コンパス自差に影響をおよぼし,その作動中と停止中では相違があることを述べた。
(4) 小型漁船は大型船に比べて,発生自差の原因が複雑で,自差修正も困難であるので,注意すべきであることを述べた。
第3章 建造方法の差異による船体帯磁と自差
建造方式が旧式よりブロック式への移行に伴い,その帯磁状態の解析が困難となり,磁気コンパス自差の修正も困難になった。本章ではその基本的な考え方にふれ,その修正法についても不十分な点を論議し,それぞれの建造方式に適合する方法について検討した。その要点を述べると次のようである。
(1) ブロック建造漁船の帯磁の特徴は,個々のブロックの建造中の履歴に関係し,船体に組み立てた後の全体の帯磁は不安定である。また,艤装中にとりつけられる装置のになう帯磁量の方が大きい。船体永久磁気の安定までには,比較的長期間の1~3年を要した。
(2) 同型姉妹船でも,帯磁はそれぞれ異なり,その傾向が一様でないが,その原因は先に述べた建造中における各ブロックの履歴に起因すると思われる。
(3) ブロック建造船の自差修正は,磁気赤道で修正装置を撤去して,永久磁気と半永久磁気の経年変化を検討することによって,正確な修正をおこなうことができる。, 第4章 磁気コンパスにおよぼす地方磁気の影響
磁気コンパスにおよぼす地方磁気の影響について,実験をおこなった結果を検討し,次の結論を得た。(1) 地方磁気が鹿児島湾の湾口に存在することを観測した。その原因については,砂鉄,鉱床の存在,火山脈等の帯磁によるものと推定した。
(2) 桜島周辺の地方磁気について,桜島の北側と,南側の近接海上では相反する帯磁が認められた。また,桜島を中心にした磁気要素を測定した。
(3) 池田湖の地方磁気は,湖の中心を通る南北線に関して,対称に,E.ly,W.lyの傾向が観測されたが,これは,湖の周辺に存在する帯磁物質によるものと思われる。
第5章 異常天文現象の磁気コンパスにおよぼす影響
異常天文現象が地球磁場に影響することは知られているが,未知な点が多い。実験の機会にめぐまれたので,磁気コンパスにおよぼす影響を実験観測して,次の結果を得た。
(1) 鹿児島県トカラ列島宝島で(1958年4月19日)おこなった金環食の観測で,船舶装備の磁気コンパスに,最大変化1°弱の誤差が生ずることを認めた。
(2) ニューギニヤ北東岸ラエ港で(1962年2月5日)日食が磁気コンパスにおよぼす影響について観測し,2.5°の最大誤差を認めたが,原因については明らかでない。(3) 1967年,5~6月の太陽黒点の異常出現が,磁気コンパスにおよぼす影響について実験観測したが,最大変化巾0.4°程度の変化が認められた。これらを総合すると,これらの現象が磁気コンパスにある程度の誤差を生ずる原因となるものと思われるが,重大な影響をおよぼす程のものではないことがわかった。},
 pages = {139--234},
 title = {漁船の磁気コンパス自差に関する研究},
 volume = {20},
 year = {}
}