† jack blockn.
Nautical. Obsolete.
A small block (block n. 2a) used to raise and lower the topgallant yards, and (perhaps) to send up the jackstaff.
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society > occupation and work > equipment > lifting or hoisting equipment > [noun] > tackle > pulley(s) mounted in case > types of
snatch-blocka1625
runnera1738
jack block1794
mufflea1830
snatch1850
fiddle-block1858
truss-block1883
spider-sheave1903
power block1928
society > travel > travel by water > vessel, ship, or boat > equipment of vessel > tackle or purchase > [noun] > system of) pulley(s) > for raising or lowering yards
jack block1794
1794 D. Steel Elements & Pract. Rigging & Seamanship I. 168 Jack-block, a small block seized to the topgallant-mast-head, for sending the topgallant-yards up and down.
1795 Minutes Court Martial A. J. P. Molloy 20 The Sail blew up against the Stay, as naturally would be supposed, the Jack-block and Sheet being shot away.
1863 W. H. Parker Questions Pract. Seamanship ii. 32 If jack blocks are used, sway the yards at the third roll.
This entry has been updated (OED Third Edition, March 2018; most recently modified version published online June 2018).
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