The design of a hydrofoil system for sailing catamarans

[摘要] The main objective of this thesis was to design a hydrofoil system without a trim and ride height control systemand investigate the change in resistance of a representative hull across a typical speed range as a result of theaddition of the hydrofoil system, while retaining adequate stability.The secondary objectives were as follows: Find a representative hull of sailing catamarans produced in SouthAfrica, and to establish an appropriate speed range for that hull across which it is to be tested. Test and explainthe drag characteristics of this hull. Find a suitable configuration of lifting foils for this hull that would notrequire any form of trim or ride height control to maintain stability throughout the speed range. Test andcompare the resistance characteristics with and without the assistance of lifting foils. Test and explain the effectsof leeway and heel on the total hydrodynamic resistance both with and without lifting foils.A representative hull (RH1), based on a statistical analysis of sailing catamarans produced in South Africa andan existing hull design of suitable size, was designed. A speed range was then established (0 – 25 knots) basedon the statistics of the original (existing) design. A scaled model (of RH1) of practical and suitable dimensionswas designed and manufactured, and its characteristics determined through towing tank testing.A hydrofoil system was then designed and during testing, was adjusted until a stable configuration was found.This resulted in a canard type configuration, with the front foil at the bow and the main foil between thedaggerboards. Although a stable configuration was achieved, it was noted that any significant perturbation inthe trim of the boat would result in instability and some form of trim control is recommended.The main objective was achieved. The experimental results concluded that a canard configuration was found tobe stable for the RH1 (foil positioning already mentioned) and the addition of the hydrofoils provided asignificant improvement only above a displacement Froude number of 2, which for our full scale prototype, isequivalent to approximately 14.2 knots.This is in agreement with the results of several other research projects that investigated hydrofoil supportedcatamarans with semi‐displacement type demi‐hulls. Below displacement Froude number of 2, a significantincrease in total hydrodynamic resistance was observed. Since the speed of sailing craft is dependent on wind speed, there will often be conditions of relatively low boatspeed (below displacement Froude number of 2). So it was recommended that a prototype design would have aretractable hydrofoil system which could be engaged in suitable conditions (sufficient boat speed).The effects of leeway and heel on the total hydrodynamic resistance were determined experimentally, but it wasfound that these trends were affected by the resulting changes in wave interference resistance. Since waveinterference depended strongly on the hull shape, it was therefore concluded that no universal trends can bedetermined regarding the effects of heel and leeway on the total hydrodynamic resistance. These effects weredetermined for RH1 and it was shown that these effects are drastically altered by the addition of the lifting foils.

[发布机构] Stellenbosch University