Hull shaping explains range efficiency

Scaling a successful hull up or down could alter hydrodynamics, stability, underwater shape, and resistance enough to spoil its efficiency. Around 450 to 500 tons, forms suited to smaller craft began working against larger destroyers. One Spahi class member, built by Dyle et Bacalan in Bordeaux, carried 115 tons of coal against roughly 95 in most of the class and reached 2,880 nautical miles at 10 knots. The extra twenty tons accompanied a gain of roughly 1,680 nautical miles, far too much to explain by fuel capacity alone. Subtle differences in the lower hull reduced the power needed to maintain cruising speed. A racing-yacht anecdote illustrates how small sources of resistance can affect performance: attempts to remove weed or barnacles improperly can create more resistance than leaving them in place. The exceptional destroyer was the only class member built by that yard. Investigators later studied why it performed so well, and the builders may not initially have recognized the effect of their hull-shaping arrangements.