Science: Pinch & Jet Ship

Ship propellers, churning out their wakes with magnificent forcefulness. look pretty efficient. But John H. MacMillan Jr., president of Cargill, Inc. of Minneapolis, suspected them of churning a little too turbulently. Since Cargill is a grain firm, deeply involved in water transportation, MacMillan decided to save his company some money by improving its ships' propellers. Last week he described a system that he believes gets more propulsive effect out of a ship's engine.

Key to the system is two deep grooves built into the hull near the ship's stern (see diagram). They converge toward the propeller, and when the ship is in...

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