The information of the characteristics of ship waves generated by a small vessel and motions of a small boat
by their waves are very important to prevent the damage of a small boat. In the previous paper, we discussed
about the characteristics of ship waves generated by three kinds of small actual boats, a displacement boat, a
high speed boat and a planing boat. As more developed research of the previous paper, this paper deals with the measurements
of motions of a small actual boat in ship waves generated by a high speed actual boat passing relatively
near her ship position.
The results of measured ship motions are compared with ones of approximate calculations. As results, the
both results of pitching motions show relatively good agreement, but the both results of rolling motions have discrepanoyin part.
In order to apply inverter-supplied induction motor drive to oil-hydraulic pump for controllable pitch propeller,
the experiment using Umitaka-maru (1829t, generator engine output 308 kW, fuel consumption 800 kg/day)
was conducted to evaluate the energy saving and practicability, conceming the dual speed drive system. The
results showed that this system on the oil-hydraulic pump was much practical use for energy saving, and the
saving fuel consumption of generator engine was estimated to be 465 kg per one cruise (93 days).
To investigate tensile breaking factors and preventive methods on the polyamide monofilament line, the
circularity and tensile strength were measured. We found out that the circularity is dispersive along the line,
which lower the tensile strength and cause the line breaking by the stress concentration.
When polyamide monofilament line is bent on swivel, tensile strength decreased as the decreasing of cross
section area. We examined the tensile breaking factors theoretically, and then discussed some preventive methods
of tensile breaking, i. e. vinyl tube, tapered polyamide monofilament, preventive frames installing on swivel and
casting polyamide monofilament. The casting polyamide monofilament has special cross section, wears resisting
and against damage, so it is suitable for the fishing operation.
We tried to investigate three methods to prevent the propeller of the training ship 'TENYO-MARU' from
being fouled by marine organisms in her home port. As a result, the more effective prevention is to use at the
same time both the method of jetting seawater with copper-ion and air on the propeller boss cap, and the method
of pouring seawater with the fomer from the clearance of stem tube to the propeller boss.
The flourishing of the seagrass, Zostera marina, was performed by using artificial seeding method on a
polypropylene mat. The commercial mat as 'sediment stabilizer mat' was used to decrease sediment disturbance
on the sand substratum off Kushiki, Naruto, Tokushima. The polypropylene mat (1mx1m, 4cm, 23 and 31kg of
weights) were made of pemeable meshes. The plants of Z. marina seeded on the mats, flourished successfully
for one and half years under the terrible environmental condition at 2m (H1/3) wave height and 10 cm fluctuation
of the natural sand bottom level in the winter season. Its shoot density on the mats was observed to
decrease after maximum individual shoots (87 shoots/m2) in the first summer season. Such monitoring of growing
Z. marina plants on the mats is required for promoting the methodology establishing seagrass beds.
A fishing net for a set-net is often covered with marine foulings while operating. We attempted to measure
a drag on the fouled nets. The test nets were soaked in a set-net fishing ground during the periods from 15 to 60
days and some water depths (1.5 to 15 m). The test nets consisted of polyester multi-filaments (0.85 mm in
diameter and 17 mm in bar length), which is commonly used for the set-net fishing gear.
The main marine foulings are fine attaching materials so-called 'Nuta', Amphipoda, a kind of hydroida
Tubulalia mesembryanthemum and a kind of moss animals Bugula neritina. The drag per 1 m2 for each test net
at the right attack angle and 0.5 m/s in flow velocity was from 3.7 kgw to 19.3 kgw. The changing ratio of drag
varied from l.4 times to 8.5 times against the initial (unused) net. The mean ratio of drag on each socking
period, however, peaked 6.5 times of the 30th days net and then it scarcely changed til1 60th days net.