Water Power: Building an Overshot Water Wheel

You'll need a good foundation because they're heavy, but if built right an overshot water wheel will be durable, productive, charming and picturesque.

| March/April 1972

Often seen beside a picturesque rural mill, an overshot water wheel possesses two excellent characteristics: considerable mechanical efficiency and easy maintenance. Many have remained in service for decades, and now lend a nostalgic charm to their surroundings.

Operated by gravity, the overshot wheel derives its name from the manner in which water enters the buckets set around its periphery. Pouring from a flume above the wheel, the water shoots into buckets on the down-moving side, overbalancing the empty ones opposite and keeping the wheel in slow rotation.

Since such a wheel may be located near but not actually in the stream, it offers endless landscaping possibilities for a country home where a stream with sufficient flow is available. If a site on dry ground is chosen, the foundation may be constructed dry and the water led to the wheel and a tailrace excavated. With very little effort, the scene may be turned into an attractive garden spot, the wheel becoming both a landscaping feature and a source of power.

It should be noted, however, that an overshot wheel is practical only for a small-capacity output. How much power it will produce depends upon the weight of water the buckets hold and its radius, or lever arm. Expressed in another way, the output depends upon the weight of water transported and the height, or head, through which it falls while in the buckets. For maximum efficiency, the wheel must use the weight of the water through as much of the head as possible. Therefore, the buckets should not spill or sling water until very near tail water.

Power Increases with Width

Although of simple construction, an overshot wheel is cumbersome in size. For this reason, before attempting to build one be certain you have the facilities to move and lift it into place when completed. Also allow yourself plenty of working floor space. It must be understood, too, that such a wheel is a sizable project and requires a lot of material and time. Extreme care in cutting and assembling the parts is not essential, however, because the wheel, operating at slow speed, need not be accurately balanced.

Our construction plans are suitable for a small wheel suitable for a water head of 6' 3". The wheel itself has a diameter of 5', leaving a flume head of 15" to propel the water into the buckets. You may build the wheel to give a power output ranging from 1/2 hp. to 1 hp. at 10 r.p.m. All dimensions remain the same except the width, the horsepower increasing as this is increased. For 1/2 hp., the wheel should be 15 31/32" wide. For 1 hp., it should be 31 29/32". Before deciding on the wheel size, you'll want to make a survey of the power available in the stream.

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