- 1). Go to the hardware store and buy two screws of the same length and diameter. One should have threads that slope significantly more than the threads of the other.
- 2). Use a screwdriver--a regular "manual" screwdriver, not an electric screwdriver--to drive the full length of the screw with the steep threads into a block of wood. Then, drive the other screw, the one with the threads that aren't so steeply sloped threads, into the same block of wood. Note that it takes more turns of the screw, but less effort, to drive the screw with the "flatter" threads into the block of wood.
- 3). Look at two boat propellers, both 14 inches in diameter. If one is a 14/12 and the other a 14/22 propeller, you'll notice that the blades on the 14/22 are more steeply angled than the blades of the 14/12 propeller.
The "14" is the diameter of the prop in inches; the "12" and the "22" are the pitch of the propeller. The 14/12 propeller moves the boat forward 12 inches for each revolution of the prop. The 14/22 prop moves the boat forward 22 inches for each revolution of the prop. That doesn't mean that the 14/22 propeller is more efficient in every case, though. - 4). Examine the trade-offs between propeller pitches. Just like the screw with the "steep" threads, it takes more effort to drive a propeller with greater pitch through the water. The screw with the shallower threads didn't take as much effort, but didn't go in nearly as fast, either; the same principle applies to a propeller with a smaller pitch.
The propeller with the "22" pitch may push the boat faster at full throttle, but it may struggle in getting up to top speed if the engine isn't strong enough, and waste a significant amount of fuel. The propeller with the "12" pitch may be more efficient at low boat speeds, but a strong engine will be operating at its maximum number of revolutions per minute long before it reaches the boat's maximum potential speed. - 5). Consult your boat engine dealer or manufacturer to determine what pitch of propeller your particular engine was designed for. The trade-off between your boat's speed and efficiency is directly linked to the motor hanging on, or in, her stern, and the pitch of the propeller on the engine.
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