| Class overview | |
|---|---|
| Name: | Oheka II |
| Builders: | Lürssen[1] |
| Completed: | 1 |
| Active: | 0 |
| General characteristics | |
| Type: | yacht |
| Displacement: | 22.5 tonnes (22,500 kg) |
| Length: | 22.5 m (74 ft) |
| Propulsion: | 3 x Maybach VL2 V-12, also used in Zeppelins[2] |
| Speed: | 34 knots |
Oheka II was a private motor yacht built for German investment banker Otto Hermann Kahn by Lürssen in 1927. Capable of 34 knots top speed, she became the blueprint for the German Navy's Schnellboot.
"Oheka" is an anagram of letters from Kahn's full name, Otto Herman Kahn.
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Born in 1867 in Mannheim, Otto Hermann Kahn was an investment banker, collector, philanthropist, and patron of the arts.
Khan approached German boatbuilder Lürssen in 1926 to build him a high-speed motor launch capable of use both in the River Rhine and the North Sea.
German boat builders at the time were used to building semi-gliding limousines like cruising boats for the Rhine, which to create a smooth ride were round bottomed. However, the problem this creates is a greater depth in the water, and a resultant increase in hydro-dynamic drag, reducing speed. While on a river, this was not of concern, in a high-speed launch it would require more power.
The first choice of Lürssen for Khan's yacht was for a round bottomed hull, to create a smooth ride. But to reduce hydro-dynamic drag, they reduced hull weight by forming a composite shell of wooden planks over an alloy metal frame. Thirdly, to counter the inefficient tendency of round hulls to "squat" stern-down in the water at high speeds, they counterbalanced it by two measures:
The result was a 22.5 metres (74 ft) length hull displacing 22tons, which was wider at the front over the rear, creating an almost perfect high-speed hydro-dynamic shape. Having perfected the hull, Lürssen equipped the boat with three Maybach VL2 V12 engines of 500hp each, which were also used to power the Zeppelins.
In Lürssen speed trials the new craft consistently reached a top speed of 34 knots, making it the fastest boat in its class int the world. There is no basis for the common misconception that Oheka II was a "rum runner" used for smuggling.[2]
In November 1929, Lürssen was given a contract to build a boat to the same basic design as Oheka II, but all metal with two torpedo tubes on the forecastle, and a slightly improved top speed. It became S-1, the Kriegsmarine's first Schnellboot and the basis for the all other S-Boats built during World War 2.