Prototype of a Single-Handed
Hydrofoil Sailing Catamaran

 

Takeshi Kinoshita1, Koutarou Horiuchi2, Hiromasa Kanou1,3, Yasuhiro Sudo1 and Hiroshi Itakura1

 

1 Institute of industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan

2 Japan Solar- and Human-Powered Boat Association, Shizuoka, Japan

3 Mitsubishi Heavy Industries, Ltd. Nagasaki, Japan

 

 

Abstract

 

A new, high-speed, recreational dinghy has been developed. At the last ICHD held in Yokohama, the concept of the boat, mathematical model used for design and the one fifth and one third model test results were presented [1]. This paper shows test results of prototype model, i.e., real scale model.

The prototype could be successfully foil-borne even weaker wind than expected in a side wind condition.

 

 

1 Introduction

 

Sailing dinghies and sailboards are very enjoyable recreations. Sailing dinghies are much slower than sailboards. A standard dinghy sails at 6 or 7 knots in a wind of 10m/sec, whereas a sailboard sails at more than 20 knots in the same wind. Sailboards cannot sail toward the windward as much as sailing dinghy can.

Conventional hydrofoil sailing boats are big and foil-borne only in a heavy wind. It is not easy to enjoy for Sunday sailors. We have designed a new type of single-handed hydrofoil sailing catamaran. This boat is designed to be able to sail toward the windward like dinghies and as fast as sailboards. Further it can easily be able to sail for an armature sailor.

It has already been confirmed that one third model could be successfully foil-borne. The mathematical model says that it can be foil-borne even in very light wind such as 4m/sec, whilst sailboards cannot plane-sail in such a weak wind, that it can sail on 20~30 knots in a nice wind such as 8~10m/sec, and that it has very good stability even in oblique waves. Then the authors made a prototype model and tried to make the predicted performance sure.

 

 

 

2 Restoring Moment against Heel Moment

 

Most of conventional hydrofoil sailing boats have half submerged foils. Areas of those foils are adjusted by height from the water surface automatically. However this system dose not has a good performance of the resistance to lift force ratio. The foils we adopted are completely submerged.

This boat attains foil-borne at a high speed by adopting a torsional structure of a catamaran.  The boat is shown in Figure 1 and Figure 2. Each hull of the catamaran rotates about a fore beam. So that the hulls twist freely and lift forces acting on the foils of each hull are automatically controlled.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 1: The prototype foil-borne (Twin Ducks)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 2: The arrangement of the prototype

 

 

 

Main foils are fixed to each hull and twist of the hulls causes difference of the angle of attack of each foil. The angles of the fore foils are controlled by planing plates. Each hull has a pivoted fore foil　which controls the height of the hull above the water, and a fixed rear foil which supports most of the weight of the boat.

We designed beams to produce a torsional catamaran. Each hull of the catamaran rotates about the fore beam (main beam), which is connected to each hull. The rear beam pierces the hull only though an inner bracket so as not to disturb the rotation.

It was confirmed that the system works well in one-third scale model in last year. Then we produced a real size model and tested it.

 

 

3 Determining of the Area of Foils

 

The area of both fore and aft foils was changed from the one third model, because the boat had better easily take off even in a weak wind. The area was made 1.5 times of one third model. The predicted performances by Kanou[3] for each area of the main foil is shown in Table 1. The taking-off-speed becomes slower as enlarging the foil area. It means that the drags of the foils and the struts as well as resistance of the hull are reduced.

 

 

4 Manufacture of the Prototype

 

4.1 Hull and Hydrofoil

 

The boat should be as light as possible in order to reduce each hydrofoil loads. The twin hulls are made of carbon fiber cloth with sandwich structure. The main and fore hydrofoils are made of sandwich of carbon fiber and wood. A main foil is replaced by a rubber wheel with rotating ninety degree in case of on-shore use. It is shown in Figure 3 and Figure 4. A strut of the fore foil also functions as a rudder. A planing plate and a fore foil are shown in Figure 5.　This system controls the rotation of the fore strut and the angle of attack of the fore foil. It has stopper cams. They keep the maximum and minimum angle of attack of the fore foil. Those angles can be asjusted by turning cams.

 

 

 

 

Table 1: Predicted taking-off-performances for each area of main foil

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3: The main foil and rubber wheel

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 4: The rubber wheel in case of on-shore use

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 5: A planing plate, a fore foil and stopper cams

 

 

 

 

4.2 Sail

 

A sailboard sail is used because of its high performance, and ease to handle. The sail is supported by stanchions as shown in Figure 6.

 

4.3 Aft Beam

 

An aft beam is shown in Figure 7. it is supported by a sliding connecter hinged to the hull, so that each hull of the catamaran rotates about the fore beam.

The principle parameters of the prototype are shown in Table 2. The boat is 72kg total weight and easy to be dismantled. The hulls can be carried on the top of a car. It is shown in Figure 8.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 6: The stanchions supporting the sail

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 7: A sliding mechanism of the aft beam

 

 

Table 2: The principle parameters of the prototype

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 

 

 

 

 

 

 

 

 

 

Figure 8: The hulls on a car

 

5 Predicted Performances [2]

 

Performance was predicted in advance by the mathematical model. Minor change is made on the mathematical model from the previous one on the following points,

 

･The crew's weight is transmitted to the hull through three points where the deck touches the hull.

 

･The sail force is applied to center of the sail area.

 

･Accurate struts area is applied.

 

Calculated results show more reality by these improvements. The results for the small and large sails are shown in Figure 9 and Figure 10, respectively.

 

 

6 Prototype Tests

 

We carried out the towing and sailing tests of the prototype at Zaimokuza coast in Kamakura.

 

6.1 Towing Test

 

We measured resistance of the boat. The results were shown in Figure 11. A maximum resistance occurred at 2.0m/sec. This result is improved 17% compared with the prediction of Table 1 (2.35m/sec). However, the resistance to the weight ratio was 12.95% at taking off from the water. This is worse 27% compared with the prediction (10.17%). It may be because of interference at the connection part of the strut and the foil.

 

6.2 Sailing Test

 

Average wind speed was 3.2m/sec. The boat took off in a puff of a wind about 4.0~4.4m/sec and top speed reached 4.7m/sec. Once the boat took off, it kept doing in a light wind about 3.3m/sec. Results are shown in the Figure 10 and compared with predictions by the mathematical model. The boat speed of the sailing tests was about 70% of the prediction. It is because estimation of the lift and drag forces acting on the foils is not enough accurate as well as measurement accuracy of the sea trial is also not enough.

It became clear that it was very difficult to sail either closed hold or in a heavy wind, and that it was due to ventilation on the hydrofoils and struts.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 9: Polar curves for small sail (6.4m2) predicted by the mathematical model

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 10: Polar curves for the large sail (10.6m2) predicted by the mathematical model compared with sailing test results

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 11: Results of towing tests

7 Conclusions

 

The prototype could be foil-borne even in very light wind such as 4m/sec. We also found out the following problems to be solved.

Ventilation occurs at the fore struts and the fore foils in the towing test at high speed, when steering by a rudder. There is strong low pressure on the upper side of the fore foil and the lee-side of the strut near the water surface. It causes ventilation.　This prototype is strong weather-helm before taking off, but it is lee-helm after taking off. It means that the arrangement of sail, hulls and foils is not enough to show its maximum ability. We should adjust it, and we must take it into account for the mathematical model to improve the design.

 

 

References

 

[1]      Inukai, Y., Horiuchi, K., Kinoshita, T., Kanou, H. and Itakura, H. : Development of Single Handed Hydrofoil Sailing Catamaran, Proceeding of the 14th International Conference on Hydrodynamics (ICHD), (2000), pp.229-234

[2]      Inukai, Y., Horiuchi, K., Kinoshita, T., Kanou, H. and Itakura, H. : Development of Single Handed Hydrofoil Sailing Catamaran, Journal of Marine Science and Technology , vol.6 (2001), pp.31-41

[3]      Kanou, H.: Prototype development of Single Handed Hydrofoil Sailing Catamaran, Master Thesis, Department of Environment and Ocean Engineering, University of Tokyo, (2002)