A deck tie down keeps the deck from being pulled up on keel stepped masts, where the mast does not sit on the deck. When the halyards are led aft via turning blocks attached to either the mast collar or the deck surrounding it, the deck will try and pull up as the line becomes loaded. The deck can also be pushed up by the compression
of the hull, typically, caused by rigging tension.
Installing one or two deck tie rods (sometimes called a “panting stay”), between the deck collar and the lower part of the mast (or mast step) will compensate will compensate for these upward loads.
When the mast is keel-stepped, it is important to
secure the deck to the mast, especially when the
halyards are led via turning blocks attached to the
deck collar. Otherwise, the lifting force of the halyards
the deck. Seldén traditional deck ring
incorporates a “tie-rod system” to eliminate this
the halyards are attached to the
collar on the deck, it is essential to
compensate for the load they exert
upwards. It is therefore necessary
to fit one or two deck tie rods
between the deck collar and
the stepped part of the mast.
From ➥ http://www.seldenmast.com/files/exce...08-E-57-59.pdf