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A composite ship is a sailing ship built by placing wooden planks over a wrought-iron frame. The use of the wrought-iron framework of a composite ship provides added interior room due to the lack of the very large wooden timbers required for strength. The composite ship design was used due to the inability to sheath iron hulls with copper. This was done to combat the forming of drag-inducing weed growth that is common in the warm tropical waters. The wooden planks could be covered with the copper sheathing, thereby reducing drag and creating faster voyages while under sail.
The production of the composite ship began in the mid-19th century and was effectively the last vestige in the development of the fast commercial sailing ship. The wrought-iron framework within a ship created a very sturdy backbone that would resist hogging and sagging while loaded. Hogging is the tendency of the ship to rise in the middle while sagging, as the name implies, is the tendency of the ship to bend down in the middle. The use of iron on the composite ship in place of the large wooden beams typically used in the ship's construction creates much more room inside of the ship while maintaining a strong design.
While nails could not be used to secure the wooden planks to the iron frame of the composite ship, brass bolts were used due in part to the ability of the brass to resist rusting and corrosion. In the early years of ship construction, copper sheathing was the only known method of covering a ship's hull to prevent the formation and growth of organic materials that were so rich in the tropical waters. This growth would slow the sailing ship substantially, costing the ship's owners extra money in wages and lost cargo contracts.
As the experimentation with iron plate hulls became common, builders realized that the organic material would grow on the unprotected iron as well. Trial applications of copper sheathing over the iron plate resulted in bimetallic corrosion, a phenomena detailing the chemical imbalance and reaction between two different metals. The composite ship eliminated this problem by allowing the copper to cover the wooden exterior of the ship. Soon, every major ship builder was forced to create a composite ship in order to compete with the fast-sailing vessels. The advancements in steam power as well as the opening of the Suez Canal ended the reign of the composite ship.
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