The primary aim of the thesis was to design a system capable of measuring the drag force on a rowing shell. The immediate motivation for completion of this thesis and the design of such a system is its potential benefit in schoolboy rowing where rowers are of differing weights. In this situation, the trim of the rowing shell largely depends on where the heavier members of the crew are seated and the effects of this trim are largely unknown. Consequently, the system was to be able to be used in an experiment to define the optimum, drag minimising trim setting for a rowing shell.
The accurate and potentially inexpensive final design of the system consists of a motorboat (minimum of forty horse power outboard motor) towing a rowing shell behind it with provision for measuring the instantaneous drag force acting on the shell for the respective shell velocity. The system consists of six sub-sections. These are the towing frame system, towing cable system, towing cable tension measuring system, shell stability system, shell velocity measuring system and a weight distribution system.
The towing frame system consists of a stainless steel frame that bolts onto the rowing shell. It features nylon washer and plate components to ensure no damage occurs to the rowing shell during testing. A dual load cell consisting of a digital displacement transducer and strain gauges (plus electrical support) completes the towing cable tension measuring system and attaches the towing frame to the towing cable which in turn is connected to the motorboat. A thirty meter long towing cable was required to avoid the surface effects from the motorboat disturbing the rowing shell and was found to have maximum sag of twenty-five centimetres. The stabilising system is made from eight aluminium riggers sporting swimming kickboards at their ends. A hull mounted impeller is to measure the shell's instantaneous velocity. The weight distribution system consists of twenty-five litre water containers strategically positioned along the rowing shell using five different load cases that simulate the distribution of rowers with various weights. All cable tension and velocity data obtained is to be transmitted wireless back to a laptop and data acquisition unit in the motor boat to provide a real time feed of the system's characteristics.
After the calculation of estimated drag forces using theory and experimental data that ranged from 421 N to 971 N, it was discovered that the theoretical estimates of 750 N and 971 N varied significantly from the 421 N drag estimate deduced from experimental data. Thesystem was designed with the worst case scenario in mind and measures a drag force with an accuracy level of ± 2% when using strain gauge data and ± 5% when using the data from the displacement transducer.
The total cost estimated for procurement, construction and operation of the system was calculated to be $3738.46. This is comprised of estimates of $2208.15 in equipment costs, $1361.89 in construction costs and $168.41 in operating costs. These estimates of cost can potentially be reduced significantly by sourcing second hand equipment and materials.
It is hoped that future work in this area will include the construction and testing of the final system designed within, increasing the accuracy of the designed system's measurements by taking into consideration the complex motion of the rowers, completing the proposed experiment to define an optimum trim setting that minimises drag for a rowing shell and finally, adapting the system designed to allow the testing of various other types of rowing shells and watercraft in general.