Results

From the results shown in figure M.1, (appendix M) the change in resistance across the speed range due to a shift in LCG is not very significant for the given range of LCG. Since the LCG of 44 gave the best resistance characteristics and would also provide the most even loading of the hydrofoils (and therefore highest stability when the foils were attached to the daggerboards and rudders) this LCG was chosen for testing. In order to predict and verify the model testing results, a set of model...

E

E.1 Balsa frame used to shape demihulls Figure E.l.a) Balsa sheets are cut into stat'ons and spines and then assembled Figure E.l.a) Balsa sheets are cut into stat'ons and spines and then assembled Figure E.1.b) Assembled frames of both demihulls Figure E.1.b) Assembled frames of both demihulls E.2 Assembly after demihulls are manufactured Figure E.2 - Picture of upside-down model without rudders and daggerboards E.3 Attachment of rudders and daggerboards Figure E.3 - Picture of upside-down...

Introduction

1.1 Brief Introduction to Hydrofoils Foils (hydrofoils) are important components of sailing craft. These are wing-like structures, located below the surface of the water, which are designed to have high lift to drag ratios (L D). The hulls to which they are attached rely on both dynamic and static (buoyancy) forces to support them and their performance is usually defined in terms of the resistance-displacement ratio (e) which is the inverse of L D. The L D ratio of well designed hydrofoils is...

Abstract

The main objective of this thesis was to design a hydrofoil system without a trim and ride height control system and investigate the change in resistance of a representative hull across a typical speed range as a result of the addition of the hydrofoil system, while retaining adequate stability. The secondary objectives were as follows Find a representative hull of sailing catamarans produced in South Africa, and to establish an appropriate speed range for that hull across which it is to be...

Hydrofoil Theory Design

Lift (L) is defined as the force produced at 900 to the free stream flow and in the plane of the foil cross-section. The lift produced by a two-dimensional hydrofoil in an ideal, unbounded fluid is given below. Where q is the density of the fluid, V is the velocity of the fluid relative to the foil, A is the surface area of the foil and Cl is the lift coefficient. Cl varies linearly with angle of attack until the onset of stall (to be discussed shortly) and is a function of the foil shape and...

Conclusions and Recommendations

The main objective of the thesis was achieved. A hydrofoil system without trim and ride height control was developed that maintained a stable running condition throughout a typical speed range. The change in resistance across that range as a result of the addition of the hydrofoil system was determined. The achievement of the secondary objectives is commented on below. A representative hull (RH1) was designed based on an existing design sailing catamaran and the speed range was determined from...

B

Comparing the WSA of a catamaran to that of an equivalent monohull. DC demihulls of catamaran C catamaran hull (both demihulls) Firstly comparing WSA for monohull and cat with same LOA and Displacement The following beam-to-draft ratios (B D) are reasonable estimates for cats and f 5 Ldc ( 2Vdc )1 3 0.794 Edc sing RHf Edc 10 (approx) > Em 8 f 5 Ldc ( 2Vdc )1 3 0.794 Edc sing RHf Edc 10 (approx) > Em 8 From figure B.1 above (taken from DL01 ) we get Sw,m 8.1 and Sw,m 7.75 Therefore Swm...

T

Figure 3.10 - Fully submerged foil with varied strut position As presented by Hoerner Hoe65 for low aspect ratio foils it was found by tapering the foils, an improvement in induced drag is made and that the tip to root chord ratio should be in the order of 1 3. This corresponds roughly to aircraft wings. Figure 3.11 below is tjie graph given by Hoerner where the correction factor k (for the resulting non-elliptical lift distribution) divided b'yt projafed aitea (A) is plotted against tip to...

Horiuchi Twin Ducks

Atlantic Proa Sail

The NPL High Speed Round Bilge Displacement Hull Series, Resistance, Propulsion, Manoeuvring and Seakeeping data, National Maritime Institute, Royal Institute of Naval Architects, 1976. BBCCFTZ05 E. Begovic, A. Bove, D. Bruzzone, S. Caldarella, P. Cassella, M. Ferrando, E. Tincani, I. Zotti. Co-operative investigation into resistance of different trimaran hull forms and configurations. International Conference on Fast Sea Transport. FAST 2005. June 2005. St. Petersburg, Russia. BD99...

Hull Hydrodynamics and Design

Wave Interference Catamaran

Since the main objective of this project involves investigating the resistance of a hull and how it is affected by the introduction of hydrofoils, it is important to understand the components of this hydrodynamic resistance. Additional components will be added with the addition of the lifting foils and the interaction between the hulls and foils will also need to be accounted for. These will be discussed in chapter 3. The first and most obvious resistance comportent is the visco 3 resistance...

Nomenclature

Resistance - displacement ratio for a hull Angle of strut away from vertical with water surface. Displacement weight weight of boat. Cavitation number Munk's interference factor Fbl FBD Fbw FDF FDL FDS FIR FKR Fmf Frfl Frfw Flr Fss Fmg FP Form factor Correction for non-elliptic lift distribution. Area projected no z projected area of foil z T transom , x max cross-sectional or WL waterplane Coefficient of resistance where subscripts are F, R and DP Coefficient lift at 00 angle of attack Depth...

Experimental Methodology and Setup

5.1 Requirements and Concepts of Towing Tank Testing A scaled model of the prototype to be tested was manufactured. In order to design an appropriate model, the standard methodology of Froude, used by the ITTC International Towing Tank Convention 1957 was adopted Ber02 . The basis of this concept for scaling hull resistance is that both Reynolds and Froude similarity cannot be achieved simultaneously and so the resistance is decomposed into frictional Rf and residual Rr components. Froude...

Computational Analysis

Thin ship theory is a potential flow model and a direct application of Michell's integral equation which was derived by him in 1898. One of the advantages of catamarans, when it comes to computational modelling is that their narrow demihulls allow for the use of thin ship theory. As described in Tu87 , the only requirement is stated that the hulls rate of change of thickness must be small. In other words, so long as the hull has a high length to beam ratio L B and the entry angle on the bow is...