Go to:

• 1 Introduction
• 2 Hull design approach
  • 2.1 Hull configurations
  • 2.2 Propulsion power
  • 2.3 Hull resistance
• 3 Results
• 4 Discussion & References

2 Hull design approach 

2.2 Propulsion power

When designing a hull, minimum resistance is the prime focus for waterbikes. Designing a hull for minimum resistance however, depends on the sailing speed under which the performance should be best.
Design speed is related to hull resistance, depending on the available propulsion power and efficiency loss. Therefore it begins with starting from the available propulsion power.

The power that humans can provide depends on a lot of factors: body shape, age, training, pedal revolutions per minute, leg position, etc. Figure 2.9 shows an indication of human power over time. Measurements [4] were carried out on a home trainer in a laying configuration. The persons involved had ages of about 25 years and from Holland (where everybody has a bike). It is expected that reducing the laying angle gives some increase of power over time. This is due to the fact that blood supply towards the legs improves.
Bikes on flat roads can go faster when the biker is laying extremely backward and the air resistance reduces drastically. In case of boats, speeds are much lower and the influence on air resistance is less, but not negligible. In many cases a laying configuration is also preferred because of ship stability behaviour against heeling.

Figure 2.9 Human power versus time, measured on a home trainer in a laying configuration

It also appears that the rates per minute preferred by humans in order to supply power vary in relation to the time period that power has to be provided along a range of 60 to 110 rates per minute. Figure 2.10 gives an impression of the average cycling rates per minute for humans [4].

Figure 2.10 Cycling rates per minute, preferred by humans for their power supply

2.3 Hull resistance

With the power supply being available, as indicated in the previous paragraph, energy to overcome the hull resistance for moving forward can be provided.
In Figure 2.11, the different resistance characteristics are shown for the hull types being considered. The characteristics are an indication for waterbikes, carrying 2 persons with a boat length of 6 meters. They depend on main dimensions, hull shape, trim and weight of the waterbike. For the hydrofoil, the wings and struts are included. Appendages such as rudders and propulsion shafts are considered as having minor influences and being equal for all configurations. L/B is the length versus beam ratio of the different hull types. The hydrofoil consists out of a slender mono-hull with side hulls and a large wing amid ship.
From the resistance characteristics, the hull energy can be derived, Figure 2.12.

Figure 2.11 Indications of ship resistance versus ship speed, 4 hull types

Figure 2.12 Indications of hull energy versus ship speed, 4 hull types

To top