This report is dealing about the results of op n water tests at the Ship Research Institute for two series of model propellers, each having the expandeda area ratio of 0.35 and 0.50. The shapes a d the principal dimensions of the propellers are shown in Fig. and the results are given in Fig. 2 Two kinds of d sign diagrams constructed from these results, one according to Admiral Taylor's method and another to Dr. Schmidt's method, are also given in Fig. 3-6.

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When a ship, which is rolling among waves around the steady heel due to wind, is attacked by a sudden gust, sometimes accompanied by the rudder action, if the work done by the gust and rudder action be greater than the reserve of her stability, she capsi es. The condition, that the capsize may not occur, can be expressed by the following relations:
C'=S_d/C_wD_w(θ_r+2θ₀) 2D₀θ₀+1/2mθ₀²>1......(A)
where S_d: dynamical stability arm, i. e. the area of t e stability curve divided by the weight of the ship, D_w: heeling moment arm (the speed of the gust assumed to be 1.4 time of the mean wind speed), θ_r: range of the stability curve, C_w: reduction coefficient determined from the fact of the reduction of wind speed near the sea level, θ₀: rolling angle. D₀: heeling moment arm due to the rudder action, m: metacentric eight.
Being given the speed and the rolling period of a ship, the waves (length and height) and wind speed, which cause the severest conditions to her heel, are to be found from the curves given in the paper. C' in (A) should be at least greater than unity, but, considering the other conditions which are not taken into account in the deduction of (A), the permissible lowest value of C' must be taken much greater than unity. C' is called in this paper the safety criterion, and can be considered as like the factor of safety in the strength of materials, and its permissible lowest value should be determined from the experiences of actual ships. Values of C' are calculated with several small-typed vessels, and given in the Table.

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[in Japanese]

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It has elapsed many years since the water tube boilers were introduced into marine use, with full success in European countries and in America. In Japan, on the contrary, this type of boiler has been used for some large cargo ships before the war and for a few kinds of War-time Standard Type of Ship under instruction of the former Japanese Navy during the war, but now no positive demands.
It is generally recognized that through the possibility of high pressure and high temperature steam usiug the water tube boiler, the higher thermal efficiency and weight reduction in total engine part are gotten. This fact mokes us profitable to adopt the boiler in this country where fuel and steel are excessibly short. Nevertheless, there are hesitations in our ship world to adopt this type for marine boiler due to li anxiety of reliability and difficulty of handling.
The prob ems on reliability and difficulty in handling. are as follows;
(1) Danger of low water,
(2) Trouble through feed water,
(3) Easiness of coal burning.
In this paper, the above problems should be investigated to clarify the reality, and if possible new design on the water tube boiler and finally the remedy to so ve these problems will be protested.

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Vast application of electric welding to ship works for weight and labour saving has required good high tensile steels, as HT and D steels, being satisfied for ordinary practice, are unsuitable for very high temperature treatment of arc welding due to their high contents of carbon and manganese.
So 13 sorts of high tensile steel of various contents are studied to improve the demerit.
Investigating the test result of these samples against mechanical properties, weldability, and strength of welded joint, Si-Mn steel (C 13%, Si 1.0% Mn 0.8%) proved to be the most suitable one.
As to the test for weldability, it seems to be necessary to examine for hardening ratio of test pieces heat-treated similar to affected zone by welding heat to raw material, and moreover to investigate the condition of ruptures of test pieces heated actually by the same manner as welding.

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During the last five years the authors have supervised 11 series of exposure tests, ranging from 6 to 25 months, of Japanese cedar samples tested in various ways to prevent attack by marine borers. Some of the new methods were applied to more than 20 ships sailing to the southern seas, but unfortunately most of them were lost or destroyed before ade_??_uate tests could be completed.
Protective methods generally in use for saving wooden ships from borers are either chemical or mechanical. The chemical method kills the borers by painting or injecting preservatives or toxicants into the wood. The mechanical method prevents borers from reaching the timber by sheathing it with sheet metal or specially treated fabric. Observation of exposure tests on materials treated by these two methods have given the following results:
1) Painting the exposed surface with a chemical substance harmful or disagreeable to marine borers such as copper paint, is commonly practiced as the most effective and practical method in use at present. This method is not permanent because the protective substance either gradually leaches out, or the coating itself is destroyed by abrasion in a very short time. Subsequently frequent docking and renewal are necessary.
2) Sheathing the bottom with an outer board with an intervening layer of tar paper has been considered resistant, but their experiments show it quite ineffective against both shipworms and boring crustaceans over a two year period.
3) Impregnating the wood with preservatives and toxicants is cons dered better than co ting, but the large amounts of impregnants necessary, and the increase of weight to the ship are undesirable.
4) So far as the weight i concerned, sheathing the bottom of a ship with thin wood impregnated with creosote or copper hydroxide is better than injecting the hull itself. But the impregn ted boards lengthen the life of the ship only until the in ected tox cants leach out of the thin wood, which is usually within a year.
No chemical method depending on toxicity lasts over one or two years.
Next they tested various methods of applying soluble urine resin compounds, which may be so treated as to make a hard, unsoluble outside layer, giving mechanical as well as chemical protect on. Results were obtained as follows:
1) Test pieces painted with urine resine compounds were not attacked by the borers after one and one half years. and after two years the test pieces were attacked slightly only at one corner where the coating abraded. The method is more effective than painting with copper.
2) The two year tests of an intervening layer of urine resin compounds give complete protection against the borers. Veneer plates with two or three protective layers of urine resin compounds may be applicable for the outer protective boards of ship.
3) Samples sheathed with thin boards injected with urine resin compounds lasted two years against borers.
4) Another important result of this method is the waterproof quality imparted to the woodtself. The weight of samples after two years test in the sea showed only 10-20% increase remakably lower than that of the other methods which allow sometimes up to 120% increase in weight.

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