|Displacement:||22.5 tonnes (22,500 kg)|
|Length:||22.5 m (74 ft)|
|Propulsion:||3 x Maybach VL2 V-12, also used in Zeppelins|
"Oheka" is an anagram of letters from Kahn's full name, Otto Herman Kahn.
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:
- a hull form that flattened towards the stern, providing hydrodynamic lift where it was needed
- forward positioning the engines, to counterbalance the stern drop
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 500 hp 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 in the world. There is no basis for the common misconception that Oheka II was a "rum runner" used for smuggling.
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 all the other S-Boats built during World War 2.
- Oheka II @ Die yacht magazine (German)
- "Motoryacht "Oheka II", 1927, Werftmodell". Europeana. Retrieved 2013-11-07.
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