Propulsion of the putt-putt boat — I

Conclusions

The putt-putt boat’s operation has two phases, ejection and suction. During ejection water is thrown out of the pipes, and dur-ing suction an equal quantity of water is injested. Even though the net mass flow is zero, the differences in the flow patterns during outflow and inflow cause a net forward thrust; thrust is mainly produced during ejection phase.

Neglecting the suction part of the cycle for dynamic analysis of the boat agrees quite well with the experimental data obtained. Moreover, modeling the boat as a kayak, rather than a flat plate gives a better drag estimate. The diaphragm just makes the puttputt sound and is not involved in the propulsion.

In the second part, the thermodynamic process involved in generating the thrust and drag forces will be dealt with.