Author(s): Juergen Stamm; Ulf Helbig; Marcus Noelle; Bernhard Soehngen
Linked Author(s): Ulf Helbig, Jürgen Stamm
Keywords: Environmental impact of leisure boats; Maximum secondary waves; Propulsion; Wake factor; Prognosis model 1
Abstract: As a vessel moves through water it generates waves this being the first main problem of environmental impacts on banks. During the movement of a short and small watercraft secondary waves become significant due to the superposition of diverging and transverse waves. Maximum secondary wave heights Hmax crucially influence the energy of a shoaling wave train and hence the impact on the bank. Since an increase of recreational boat traffic is to be expected, those effects become more important. The modified approach of Soehngen (2010) based on the empirical approximation by Maynord, with the consideration of the different operation modes, is the most convenient for estimating the expected wave heights. To realise a comparison with the calculated values, a concept of in-situ tests was developed. Therefore nearly 400 controlled runs were made with six different boats of various lengths (2. 6 to 12. 0 m). The boat speed and the location of the sailing lane were varied with the purpose of surveying the performance in different water depths. With diverse wave gauges wave heights could be measured at several distances to the sailing lane. The largest secondary waves were observed during the semi-planing mode. Using the collected field data an analytical comparison to the calculated approximation can be realised. Specific relations to the wave theory are found and discussed. In addition to the secondary wave generation, the second main problem of a running boat has to be explored. Which hydraulic load caused by propulsion is possibly generated beyond a boat, especially in shallow waters? In order to clarify this question, bollard pull tests were conducted. Finally, the approaches and models validated for inland water vessels also principally apply for recreational boats. However, some modifications must be done. Soehngen’s / Maynord’s approach has to be modified and extended. All three driving states of a boat (displacing, semi-planing, planing) can be described with empirical formulae. The boat’s displacement and its velocity are the main factors. The effect of the propulsion strongly depends on the propeller characteristics, the wake factor and the induced initial velocity.
Year: 2013