In order to clarify the motion characteristics of purse seiner in waves, the motions of an actual purse seiner,
135 GT size, meaｓured during searching for a shoal of fish.
The roｌｌing and pitching angles were obtained by using a vertical gyro during a series of trial runs at five
headings to the dominant wave direction (C1 to C5) under four sea conditions (S1 to S4). These recorded data
were digitised at 0.2 second intervals and analysed by means of statistical and spectrum analysis. Further, we
have investigated the seakeeping quality from the safety running point of view.
Based on the results, the probability of deck-edge immersion due to roll is also discussed.
The mechanism and process of the fomation of tidal flat, settling properties of suspended sediments (SS) in
shallow sea water have been investigated through laboratory experiments and field measurements.
The results suggest that settling properties of SS were influenced by the type of sediment, SS concentration
and salinity of sea water. Interpretation of the variation in both SS concentration-time and grain size distributiontime
with depth yielded a good qualitative description of the settling and deposition processes. An attempt has
been made to develop an expression for the interfacial settling velocity of SS from the theoretical considerations
on the basis of the two-phase flow theorem of a fluid-sediment system. The experimental results agreed well
with the theoretical values of the mean interfacial settling velocity of SS.
Theory on upwelling generated by submerged obstacles being placed normally to the bottom flow is
developed and verified by hydraulic experiments. Upwelling device consists of two vertical plates being parallel
to each other. Experiments show that the upwelling is generated intermittently owing to emitting the energy
produced by the pressure difference between inside and outside the wake formed behind the vertical plate. On
the bases of the experimental results, We developed the upwelling theory in which we assumed that the upwelling
energy is equal to the emitting energy.
The theory shows that the rising height of upwelling waters depends on the pressure head decrease in wake,
the height of upwelling device and the horizontal distance between two vertical plates, and the intermittent
generation period of upwelling depends on the dimensions of upwelling device and the main flow velocity. It
is also shown that the volume of upwelling water depends on the the total energy of the pressure head decrease
Selection of spawning ground and spawning bed in oval squid, Sepioteuthis lessoniana, was studied in use of
four different types of man-made spawning beds settled in the coastal waters of Tokushima prefecture. Under-
water observations and sampling of egg capsules were carried out by SCUBA diving during a period from May
1990 to September 1993. The number of egg capsules laid on the man-made spawning bed placed in the calm
waters of the inlet was much more than that in the ground facing to the open water. The number of egg capsules
laid on man-mnde spawning bed was ranked by the bed type as, mid-water cage type > steel type > fiberglass
reinforced plastics (FRP) type, with small difference. These three types of man-made spawning beds were
recognized to be superior in respect to the mass of laid egg compared with the neighboring natural spawning
beds composed of Sargassum and Zostera. The results obtained suggest that spawners prefer a calm waters, and
select in relatively wide range of artificial materials for egg-laying.
A suevey, ｖia bean trawl, of the abundance, type (plastics, fishing gear, textile and other) and distribution
of litter was conducted on the sea-bed of an area in the central portion of Tokyo Bay. Over 4 years period
(1989-1991 and 1993) of the litter, plastics (synthetic polymer resin) made up 80-85 % of the total, with 60%
of these plastics being of low specific gravity (range 0.86-1.1).
These substances due to them being relatively inert and widely distributed pose a sigrlificant pollution threat
to fishing grounds and the nearshore marine environment. Litter from fishing activities although quantitatively
small were also sigrlificant and pose potential damage to resources via'ghost fishing, after being discarded.
The discharge volume, the quality of reservoir water and the change of water level in the bay and the reser-
voir were measured in a small-size tidal dam constructed in Uranouchi Bay.
The results of a field model test are as follow.
1. The tidal dam using the potential energy of the tide is very effective for improving Uranouchi Bay because
the tidal range in the bay is larger than out of the bay.
2. Two-Pipe-Type can be use the tidal energy more effectively than that of One-Pipe-Type.
3. The water quality in the reservoir of Two-Pipe-Type is better than One-Pipe-Type.
4. It is suggested that the attaching organism to the pipe wall increase the friction factor of the pipeline.