Hull Resistance Research Articles

Development of a New Hull Form with Semi-Submerged Bow for High Speed Craft

To improve seakeeping quality some advanced high speed crafts have been developed and in service. However, in view of total performance including building cost, operation and maintenance cost, they are not satisfactory in commercial use. Under this circumstance, a new type of high speed craft having a submerged torpedo-shaped body under the bow bottom of conventional monohull high speed craft was developed. This new type of craft with Semi-Submerged Bow (SSB) has improved seakeeping quality with comparable total performance of conventional monohull type high speed craft. In this present paper, procedure in developing this new type of craft are explained.First, as a preliminary study, theoretical calculations were made before tank tests to confirm effect of a submerged body for the reduction of ship motion in waves.Next, preliminary tank tests were carried out in waves with two small models of 1. 4 m in length (SSB and Conventional monohull) towing at the same time in parallel position to compare directly the seakeeping quality of SSB and conventional monohull and hull resistance of two models were also measured to evaluate propulsive performance.Based on this preliminary study, an initial design of a large high speed passenger craft of SSB hull form was made.Then, applicability of this type of hull form to actual ship was confirmed with some additional experiments by use of small models.Finally, tank tests were carried out by use of a 3. 8 m self-running model to evaluate quantitatively both seakeeping quality and propulsive performance.It was found from the test results that the bow acceleration in waves was reduced considerably and the effective horse power was almost comparable to conventional monohull in the speed range of conventional use.

クラスター分析による漁船の分類

With 20 variables taken as principal items of 56 fishing boats in seven types, classification of fishing boats was made in accordance with principal components analysis and cluster analysis, in combination. Verification of result was made by using data of 54 tuna long line fishing boats not used in those analyses. As the result, an existing method of classification, that is, a method of classification, set up according to uses, proved to be a suitable one. Hence, the classification by use of the fishing boat has quite an important meaning, and the fishing boat has characteristic features essential for the performance of its function. Here, the factors such as, for example, length between perpendiculars, molded breadth, molded depth and coefficient of fineness should be considered. It is, concretely speaking, true that we can decide such factors practically only from energy saving viewpoint neglecting the use of fishing boat, but we are afraid that the fishing boat, the type of which is designed to lighten hull resistance, has, practically speaking, a serious defect in terms of efficiency required in its operation.

A statistical method for calculation of resistance of the stepless planing hulls1

A mathematical model is presented for predicting the resistance and trim angle of bare stepless planing hulls in calm water for volume Froude numbers 1 through 4. The model is based on the data relating to the systematic Series 62 and 65. For derivat

コンテナ船, Ro/Ro船の輸送性能分析

Container- and Ro/Ro-vessels are featured especially by the reduction of terminal time as a result of containerized cargo handling of lift-on/lift-off and roll-on/roll-off method, respectively. This paper analyzes the transportation energy efficiency of both vessels built in Japan so far, with paying attention to the feature mentioned above. Firstly the hull resistance characteristics are analyzed. In the same as car ferry, both vessels have the property being able to separate the hull function into buoyant support and cargo vessel. This property permits the hull form to have less resistance than general cargo ships. The performance level of hull resistance is same for all container-and Ro/Ro-vessels except the large, high speed container vessels with the speed above 26 knots and the displacement above 50, 000 tons, of which hull form are different because of the Panamax limit, and result in inferior level by about 30%. It is pointed out, therefore, that the enlargement of hull size over the Panamax limit is excessive as for the container ship. Secondly the cargo performance, which is indicated by the payload-to-displacement ratio, is analyzed. The payload of container- and Ro/Ro-vessels can be regarded as the carrying number of containers. The above ratio of container vessel is mainly determined by two factors of deadweight-to-displacement ratio and container number on deck loading. The deadweight-to-displacement ratio raises undesirably with speed. While it cannot be improved by the increase of displacement. Therefore the high speed container ship above 26 knots cannot have necessarily good cargo performance in spite of the design for increase of container number on deck loading. The cargo performance of the Ro/Ro ship is worse by two times than the container ship due to the roll-on/roll-off cargo handling method. This demerit sets off inevitably the merit that the Ro/Ro ship can handle cargoes without the special equipment ashore.

カーフェリの輸送エネルギ効率について

Recently, in Japan, the transportation by the car-ferry, especially by the long route car-ferry of which important cargos are trucks, is remarkably growing. This paper analyzes the characteristics and the present status of the car-ferry transport energy efficiency with regarding the role of the ferry as an alternative way of the land transportation by the truck. The hull resistance and propulsion efficiency of the ferry are better than the common cargo ship. This characteristic is due to the capability of differentiating the hull function into the buoyant support function and the shipment function. The payload-to-displacement ratio has a great influence on the transport energy efficiency of the ferry. This ratio is determined by the carriage deck area. Therefore the catamaran type hull is very favorable for the ferry.The estimation based on the actual transport energy efficiency reveals that the ferry transportation consumed about 1.4 million tons of oil fuels at 1975 in Japan. The ferry transport energy efficiency is estimated by the comparison with the land truck transportation. The result shows that, at the present, the small and medium sized ferry are worse than the truck, but the large sized, that is, long route ferry can compare favorably with the truck. The improvement of the payload-to-displacement ratio would extend the region where the ferry could be used as an alternative way of the land truck.

Free Surface Shock Waves and Methods for Hull Form Improvement

A new method of designing hull forms of minimum wave resistance is developed in which two major components of wave resistance, i.e., one due to free surface shock waves and the other due to linear waves are taken into account. A procedure of extracting wave profiles due to free surface shock waves is proposed, which is utilized as a quantitative measure of the magnitude of free surface shock waves. The relation between hull form and resistance coefficient due to free surface shock waves is empirically derived and it is incorporated into the wave-analytical procedure of obtaining hull forms of minimum wave pattern resistance, so that the sum of wave pattern resistance (linear wave resistance) and resistance due to free surface shock waves (nonlinear wave resistance) is minimized. The effectiveness of the new method is demonstrated by experiments.

内航中小形船の輸送エネルギー効率の現状とその改善

At present small- and medium-sized vessels under 2000G/T occupy 97.3% of the total number and 65% of the total gross tonnage of Japanese coastwise shipping, and they carry 65% of cargo volume (ton·kilometers) by homewaters. Firstly this report researches the present situation of the fuel consumption and reveals that those small- and medium-sized vessels consume about 80% of the fuels for the freight transportation by homewaters. Therefore small- and medium-sized vessels, especially cargo-boats and tankers, should be paid attention for the fuel economy. So secondly the actual condition of the transport energy efficiency of those vessels is researched. The three main factors, which determine the transport energy efficiency, that is, hull resistance, propeller efficiency, and payload-to-total weight ratio are discussed in regard to present vessels. The result shows there is some room for the improvement of about three main factors, especially, with respect to the hull resistance and the propeller efficiency. Finally the report estimates that, if the former would be reduced to the level estimated according to the Yamagata's method, and if, as for the latter, the propeller diameter would be increased so far as the after draught at ballast voyage permits, then the amounts of fuel consumption could be cut down to about 64% of the present one.

Procedures for Hydrodynamic Evaluation of Planing Hulls in Smooth and Rough Water

Recent Davidson Laboratory basic studies of planing hull hydrodynamics have produced a wealth of technology which is not generally available to the small-boat design profession. Included are studies related to the preplaning resistance of transom-stern hulls, the effectiveness of trim control flaps, the effect of bottom warp on planing efficiency, the influence of reentrant transom forms, and the seakeeping of planing hulls. The present paper consolidates these results in a form suitable for design purposes and illustrates their application in predicting planing performance in smooth and rough water.

A Theoretical Approach to the Self-Propulsion Test of Full Ship

With increase of fullness of ship, the self-propulsion test is becoming more and more difficult because of many causes such as flow instability and decrease of measured quantities, etc. So each model tank is improving its own method of the test.In this paper, the authors present a theoretical approach to the self-propulsion test of full ship, which utilizes measured hull resistance and wake data. The full ship adopted here consists of the actual ship form and the infinitely bladed propeller. One side of the after body surface of the ship hull is divided into 180 (12×15) platelets. Solving the hull surface boundary condition by Hess-Smith's method, the densities of platelet sources are determined. On the other hand, the propeller plane is divided into 180 (5×36) sectors and the strength of bound vortex is assumed to be constant in each sector. Solving the propeller plane boundary condition using the wake data, the bound vortex are determined. From the source and vortex distributions, the thrust and torque-of the propeller and the increase of the hull resistance are calculated. Then the thrust of the propeller and the resistance of the hull are made to be in agreement by iteration procedure and at the end the self-propulsion factors are obtained by the thrust-identity method using the results of open water tests on the propeller. Here the contraction of flow due to propeller suction is taken into consideration in evaluating the nominal wake distribution for the full load condition. The presence of the rudder and the viscous part of the thrust deduction and the wavemaking phenomena are ignored in the calculation. The obtained results seem to be reasonable.

Effect of Tunnel Entrance Configuration on Thruster Performance

The paper is concerned with the effect of tunnel entrance configuration on thrust produced and hull resistance augmentation. A means of determining equivalent fairing radius is presented, and model test data from two sources are correlated with a limited number of full-scale tests. A method of determining whether resistance will be increased by the addition of a thruster tunnel is postulated. This method is checked against one set of model test data with two thruster tunnels, one forward and one aft, from which a drag coefficient for faired entrance sections is derived.

Some considerations on the resistance of planing hulls

Some considerations on the resistance of planing hulls

Series 64 Resistance Experiments on High-Speed Displacement Forms

The speed-length ratios of displacement-type surface ships in the past were limited to under 2.0. In order to perform projected tactical missions, however, the Navy needs ships of much higher speeds resulting in speed-length ratios of 2.0 or above. To gain information in this respect, 27 models of conventional hull forms designated "Series 64" were designed, constructed, and tested at the David Taylor Model Basin. This paper reports the results of the bare hull resistance tests of Series 64 models.

Effect of a Bulbous Bow upon the Resistance of Ships with Small Length-Beam Ratio and Large Block Coefficient

In case of oil tankers with large CB and small L/B value, the action of large bulbous bow in contributing to reduction of hull resistance is considered to be somewhat different from the case of high-speed, small CB vessels. Authors examined the results of model experiments in towing tank and in wind tunnel, and results of trial runs of actual ships on large tankers, which were all conducted by Hitachi Shipbuilding and Engineering Co., Ltd., and besides, give some theoretical considerations on them. Consequently, the reasons why a large bulbous bow contributes to reduction of hull resistance were explained, and a guide to design of the bulbous bow was given for large oil tankers.

Crash-Astern操縦の停止距離に及ぼす船の旋回の影響(日本航海学会第32回講演会)

The stopping ability of a ship is usually represented by the so-called "head-reach", which is measured at the official backing test. Head-reach is defined as the distance traveled by the ship along the locus of her centre of gravity. It must be noted, however, that the head-reach traveled by a ship when turning is shorter than that traveled by the ship proceding on a straight course. This discrepancy of head-reach is mainly caused by the appearance of a drag component of the centrifugal force due to ship turning. The paper is concerned with pointing out the noticeable discrepancies between calculated and full-scale test results of these rather complicated crash-astern manoeuvres. The author proposes that the value of head-reach obtained from an official backing test should be corrected by considering the increment of effective hull resistance due to turning of the ship.

Graphs for predicting the ideal high-speed resistance of planing catamarans

This report presents graphs by means of which the high-speed resistance and trim of catamaran planing hulls of a wide range of sizes and proportions can be determined. Graphs which give guidance in selecting parameters which will result in optimum pl