"Splice the mainbrace" is an order given aboard naval vessels to issue the crew with an alcoholic drink. Originally an order for one of the most difficult emergency repair jobs aboard a sailing ship,
Grog
…Pusser's Splice the mainbrace Brewer's Dictionary of Phrase & Fable, Millennium Edition, revised by Adrian Room, 2001…
Canadian sailors aboard HMCS Prince Robert line up to splice the mainbrace in celebration of V-J Day.
A sailor on board HMS York measures out tots of rum for the ship's company