In the first and the second report of this series, the author showed the grabbed weight Ws are determined by the grab-bucket weight itself Wg, opening length L, and the width of blade B attached to it, that is following relation ws/wg-L√B/2Wg was established among them.
　And as for the relation between grabbed weight and number of the rolling wires attached to bucket, we found the tendercy of the change of grabbed weight and number of the rolling wires, if we class by the type of bucket by their values L√B/2Wg.
　According to the research results above mentioned, the shape and form of dredging grad-bucket which is used in our country today, especially as for the general hole-tine, and half-tien type, are considered to be too small when they grab such granular-materials as sand, gravell.
　This means that we can increase the grabbed weight Wg and improve the working effciency, if we try to make such grab-bucket whose values L√B/2Wg is bigger with out changing the grab-weight Wg.
　These conclusions may be true as far as the experimental results so far conducted are concerned.
　But the truth is that we have to research on some problems such as the state of sea-bottom and mechanical points of grab-bucket including these conclusions.
　Therefore the author experimented mainly on the stress of each materials which comopse the grab-bucket. on the impact stress of it at the touch of the grabbed materials and on the resistance power affected on grab-bucket in water, and showed records here in this report.
　According to the experimental results, the author concluded that as for dredging grab-bucket, we have to investigate the use of new type grab-bucket which is lighter than half-tine grab-bucket and whose value L√B/2Wg is bigger for the granular sand and gravel.