Slove bulb – Wikipedia
And bow is a part of the shell of a boat: it is a bulge at the front, at the Brion, below the bow.
The main function of the bow bulb is to create a wave at the front of the normal wave system generated by the ship on the way; At a certain speed, the hollow of this additional wave coincides with the top of the wave of bow, which is canceled: hydrodynamic resistance is thus reduced and the ship can go faster for the same power. In addition, the first wave crest is moved to the front, which virtually increases the length to the float of the ship and therefore its theoretical maximum speed. An improvement of 20% of the resistance can be hoped with a bulb, but it will often need preliminary tests.
However, this system only works for a given speed and immersion. It is mainly applied to charging ships which generally only know two types of navigation: full load or legence, and at fixed speed. It is also applied to warships such as frigates who need speed [ first ] .
He is counterproductive in the event of a slow speed [ 2 ] .
If most of the current giant merchant ships are equipped with it, the new container ship of 23,112 Twenty feet equivalent (EVP), CMA CGM Jacques Saadé has a right bow without bulb [ 3 ] . It is the same for his eight Sister Ships.
A bow bulb also involves major construction constraints, because it is difficult to design it with developable surfaces, easier to build. On small boats, the drift surface and the submerged volume also changes considerably with the addition of a bulb; It is rarely applicable to small boats. A bulb is also directly subject to the shocks of meeting with the waves, especially in cases of tossing (also called slamming ) [ first ] .
Bulbs can also experience other uses, such as on oceanographic ships where they can serve as observation points, or on the frigates where they house a Sonar dome.
The famous Calypso , the oceanographic ship of Commander Cousteau was originally a small, American wooden mines (amnetic material) from the US Navy military surplus and recycled in transborder ferry in the Greek islands.
Of course it was devoid of bow bulb (impossible to make in wood).
Bought by the billionaire Loël Guiness who entrusted him to Cousteau, the Calypso was equipped with an underwater metal observation chamber in catwalk and welded sheets (with portholes) which can accommodate an observer, and bolted in front of the original bow.
Cousteau indicates in its memories that this false nose, in addition to its scientific utility, practically gained a speed of speed to the hull while generating significant fuel savings.
On the other hand, the uselessness of the bulb on the shells of very mobile sailboats and subject to the cottage under sail was cruelly and involuntarily demonstrated by the sail champion Paul Elvström, multi Olympic sail medal that had been expected to skip by Baron Bich To direct a French challenge in the America Cup.
At that time (mid -1970s), the cup was running with long, narrow and very weighted boats, the 12m JI (about 22 m Out of everything in reality, the term 12 m being only a coefficient calculated by a mathematical formula), but there were also smaller series as part of this same international racing gauge: the 5.5 MJI, the 6m Ji (actually measuring ten meters out of all) and 8mji.
Eager to experiment with a new drawing (the 12m ji gauge was a kept hunt for the American naval architectural cabinet Sparkman and Stephens) Elvström, associated with the Danish naval architect Jan Kjaërulff, tried to adapt a bulb on a 6mji to validate The concept by a “half -size” test after tests on a hull basin model that seemed promising.
The result was a disaster, which sneered the entire specialized nautical press:
Even crossed by the great Danish champion the 6mji “bulbous” “picked up the brooms” in the world championship of the series, systematically ending the last of each round of the regatta [ 4 ] .
The Eruptive Baron Bich “landed” then dryly Elvström and had the France 3 Much efficient due to Johan Valentjin and Ben Lecxen (who will later realize the famous Australia II the first non -American sailboat to win this “Everest de la sail”).
A cruise sailboat provided with a bulb, also drawn in the process by the Kjaerulff – Elvström tandem made only a discreet commercial career [ 5 ] . Characteristically, this “fifty – fifty” (hybrid sailing boat – engine) walked very properly to the engine, with a zero cottage and by flat calm, but was less efficient than equivalents without bulb, under veil, lodged and per sea formed.
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