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Bom-Trawlen (Fig. 19) bestaar af et poseformet, mod
Bagenden spidst indsnævret Net, hvis Mundings Overkant
er’fastgjort til en. 4.m7 (15 Fod) lang.- rund Bom af Træ.
paa hvis firkantede Ender er indsmøget Jernmejer. O’".8
(21; . Fod) høje. paa hvilke Apparatet kjøres langs
Havbunden. Trawlens Længde fra Midten af Bommen til
Spidsen af Nettet er 6m.5 (21 Fod). Den med Blystykker
belastede, noget slakke Underkant af Netmundingen er i
sine Ender fæstet til Mejernes Underdel og slæber langs
Bunden mellem disse, idet den graver mere eller mindre
dybt ned i Bundens Materiale. Gjennem en Hanefod af
Tougverk, der er fæstet i Øjebolte paa Forkant af
Jernmejerne. staar Trawlen i Forbindelse med Skrabetouget.
Til Mejerne og til Netspidsen fæstedes ofte Hampsvabere.
Maskerne i Nettet var oprindelig temmelig aabne,
saaat det kun kunde holde større Gjenstande tilbage,
medens mindre Dyr og det fine Slam gik igjennem. Efter
Professor Sars’s Ønske blev derfor Spidsen af Nettet foret
med finmasket Garn. saaledes at det kunde holde fint Slam.
Med denne Forbedring var efter vor Erfaring Bom-Trawlen
et udmærket Bundskrabningsapparat. Den fangede baade
under hurtigere og langsommere Bevægelse langs Bunden
og tog ikke alene Fiske og andre Dyr. der bevæger sig frit
i Nærheden af Bunden, men den skummede ogsaa det øvre
dyrhöldige Bundmateriale af, ja tog endog Stene og det
store, indtil 50 Kilograms (100 Pd.) Vægt ind i Nettet.
Bom-Trawlen havde i sin oprindelige Skikkelse ogsaa
den Fejl. at hele Systemet kunde svinge sig rundt i Vandet
under Ud ti r i ngen, og Apparatet kunde saaledes undertiden
falde paa Ryggen, med Bommen ned. paa Havbunden.
Denne Mangel blev rettet af Skibsfører Grieg ved at hænge
et Lod i slak Bugt mellem Mejerne. Fig. 20 viser dette
Arrangement. Naar Trawlen begynder at helde fra den
rigtige Stilling, i hvilken den blev sendt ud, afslakkes den
Del af Touget, der var fast i den Mej, som var nederst.
Loddet trak i den anden Part alene og drog den Ende,
som var øverst, ned til samme Højde som den anden.
Til Skrabetoug brugtes 5 centimeters (2 Toms) Toug
de første 2000 Favne og 6.5 centimeters (21/. Toms) i
Agterhaanden. Begge Slags var af bedste Sort russisk
Hamp. og Prøvetrosserne besigtigede og prøvede ved
Carl-Jphausværns Værft.
Forberedelser til Bundskråbning. — Disse begyndte i
Regelen strax efter at man var færdig paa Bagbord Side
med Lodning eller Temperaturrække.
For at compensere Virkningen af Skibets og Skrabens
Bevægelse paa Stramningen af Skrabetouget, navnlig for at
undgaa farlige pludselige Ryk. var Skrabetouget vist
gjennem en Blok. der hang i en Accumulator.
Skrabeaccumu-latoren var meget større end Loddeaccumulatoren. Den
havde 30 Stropper, af samme Slags soin de ved Lodningen
benyttede. Træskiverne, gjennem hvilke Tougstjerterne gik,
havde en Diameter af 0™.605 (1 Fod 11’/,. Tomme) og en
Tykkelse af 0m.050 (1.9 Tomme). Skrabeblokken var af
106
Fig: 19 represents the Beavi-trawl used on the
Expedition. A conical netted bag is suspended by one side
from a round beam of wood 15 feet in length, to the
square ends of which are fixed iron runners. 2 feet and
a half high, that support the apparatus when riding over
the bottom. The length of the trawl, measured from the
middle of the beam to the apex of the bag, is 21 feet.
Ihe lower side of the mouth of the net. weighted with
rolls of sheet-lead, hangs loose, and is fastened at either
end to the bottom part of the runners, between which it
drags along the sea-floor, scooping up more or less of solid
matter. This trawl is attached to the dredge-rope by means
of a rope crow-foot, lashed to eyebolt-^ on the fore part of
the iron runners. We often fastened hempen tangles both
to the runners , and to the end of the bag.
The • commercial trawl, as furnished by the. English
maker, had a rather wide-meshed bag; and hence it brought
up none but comparatively large bodies, small animals
and fine mud being washed through. At the instance,
therefore, of Professor Sars. the bottom of the bag was
lined up to a certain height with yarn netting,
Sufficiently close to retain the finest mud. With this slight
modification, we found the beam-trawl a most efficient
instrument, whether quickly or slowly worked; it not only
secured fishes and other marine animals that occur near
the bottom, hut skimmed off a thin layer of the surface;
nay., it would take in stones, some of them weighing as
much as 100 pounds.
In its original form, the beam-trawl was apt
moreover to capsize in the water and reach the bottom with
the beam down. Captain Grieg remedied this defective
tendency by suspending one of the cast-iron sinkers in a
slack bight between the runners. This arrangement is
shown in Fig. 20. So soon as the trawl begins to incline
from the right position given it at the commencement of
the operation, the part of the rope made fast to the
runner then deepest in the water will get slack, and the weight
accordingly act only upon the runner at the opposite
end of the beam, pulling it down to a level with the
lower one.
The Dredge-rope, samples of which had been examined
and tested at the Royal Dockyard of Carljobansværn, was
of the best Russian hemp. The 2000 fathoms next the
dredge were 2 inches in circumference, the remainder had
a circumference of 21/. inches.
Preparations for Di edging — As a rule, the gear
was got ready immediately after taking — on the port side
— a sounding or a serial temperature.
With a view to take off the suddenness of the strain
on the rope caused by the scraping of the dredge or the
motion of the vessel, the Vope was rove through a block
suspended to an accumulator. The accumulator provided
for the dredge exceeded considerably in size that used
with the sounding-machine. The number of straps was 30.
and the wooden disks through which the lanyards passed
had a diameter of 1 foot lll/i inches and a thickness of
2 inches. The dredging-block was of iron, similar in con-
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