Small sailboats often have daggerboards instead of fixed keels, and the daggerboard is inserted in the daggerboard box.

A larger sailboat with a raisable keel can be fitted with a keel box that serves as a 'pocket' to receive the keel when it is raised.

refs:

http://www.dandwboatworks.com/News3.htm
(construction photos of a sailboat with a daggerboard box)

http://tinyurl.com/2nmlsf
(sailboat construction with a keel box)

and from GWNT:

kuil ter diepte van 2 m in de kielkade, met ramen van zware balken, waaraan de onderste blokken van de kielgijns worden genaaid

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Note added at 1 hr (2008-03-20 14:54:24 GMT)
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and one more (Dutch)O

http://www.minisail.nl/gallery1/main.php?g2_view=core.ShowIt...