What is the connection between buoys and oxen?

Well, the word buoy comes from the Middle Dutch boeye (float, buoy), from the Old French buie (fetter, chain), probably from Frankish *baukan (sign, signal), the root of the English word beacon, or from the Latin boia (a (leather) collar, band, fetter), from the Ancient Greek βόεος (bóeos – of ox-hide), from βοῦς (boûs – ox), from the Proto-Indo-European *gʷow- (cow) [source].

How do you pronounce buoy, by the way?

I pronounce it [ˈbɔɪ], as in boy, but I understand that some pronounce it [ˈbuːiː] or [ˈbui], like bwee.