A cross tree is a structural support on a sailing vessel that supports the mast. It is made of durable timbers and is carefully fixed in place to withstand harsh conditions. Replacement is ideally done in a shipyard.
A cross tree is a structural support on a sailing vessel, used to support the lines, known as mortises, that support the mast. It is part of the rig known as the top, and is also known as a crossover, depending on regional spelling preferences. Other ships may use devices known as spreaders for a similar purpose. More generally, a cross tree is any type of horizontal support beam, such as a beam placed to tie up horses in a stable.
Each mast has two crossed trees, located on each side of the mast. The shrouds join them and run onto the deck. Providing support from both sides, they keep the mast securely in place, even in harsh conditions. Sometimes other anchor lines will also be placed along the length of the mast. The rig can be placed on the cross trees of the mast for various purposes and the entire rig is carefully designed to avoid tangling or nicks in the lines, as this could pose a safety concern for the sailors and people on board.
These structural supports are installed with care, as they must be able to withstand pressure and withstand hash conditions. Salt fog and ultraviolet radiation can be found in abundance around a ship and both can be very damaging. Durable timbers are used and may be tarred or otherwise treated to make them stronger, and the cross tree is carefully fixed in place to ensure it does not sag under stress. She is also regularly inspected by sailors for signs of wear, along with other aspects of the mast and rigging. Cross shaft failure could be catastrophic and this section of the ship is very important.
When ships are designed, the designer thinks about the types of stresses on board and the conditions in which the ship will be used and addresses these concerns. This can include movable rigs to meet special needs, as well as variable rig designs for different types of vessels. Most ships today primarily use masts for communications apparatus rather than navigation rigging, as other modes of power are available, and the cross-tree can serve a dual purpose in supporting equipment.
Replacement of worn and damaged cross shafts is ideally done in the controlled environment of a shipyard, where the ship can be stripped of rigging for maintenance. The mast will need to be carefully lowered and often serviced at the same time, checking for cracks, rot and other signs of wear to determine if it should be replaced as well.
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