LITERATURE REVIEW
Two designs are currently on the market. The first is a sheave drive system that steps the
shaft down and powers a prop on the shaft. This idea works well but stiffers from an
abrupt transition from the boat hull to the sheave housing when sand bars are
encountered. The second idea, the proposed design, is a long-tail, direct drive shaft. The
only rotating part of the motor that touches the water/mud is the prop. This design is
more practical due to its gradual transition as it overcomes underwater obstacles.
A search was conducted for a surface drive boat motor. It was concluded that a short
shaft design can operate at essentially water depths of 0" as long as the ground is muddy;
but this is not always the case. Gerhart (2009) discussed problems with this type of
system. V -belts are typically used to transfer power from the motor to the propeller.
Slippage occurs as water penetrates the housing. To avoid slippage, chain drives were
designed. The problem with this design is that if the chain fails, damage to the housing is
irreparable. Figure 2 shows a short shaft mud motor.