You need to make sure your equipment has the best chance to arrive safely.
What is Sea Fastening and Voyage Bracing?
When you need to ship a large crane or piece of material handling equipment across an ocean, the crane will be subjected to ship motions during the voyage. These motions are called heave (up and down), surge (fore and aft), sway (side to side), roll (tilting to the sides), pitch (tilting fore and aft), and yaw (spinning about a vertical axis). The crane will also be subjected to heel (tilting due to wind forces) and wind loads. The amount and magnitude of each motion depends on many factors like ship response characteristics, sea state, and heading. These voyage motions and heel translate into voyage loads on the crane. The magnitude of the loads will depend on where the crane is located relative to the vessel center of motion. The smallest loads are generated at locations close to the vessel's center of motion, like down in a cargo hold. If a crane will fit into a cargo hold, there is usually little need for special fastenings or bracing. Modern container cranes will not fit into a cargo hold, and are usually shipped on special heavy-transport vessels or barges. They are exposed to weather, and usually all or a majority of the crane is well above deck level. Because many of the crane's components are a significant distance from the vessel's center of motion, the voyage loads can be huge - well beyond the capacity of the crane to resist them.
Most large cranes are not designed for voyage loads, and can easily be damaged, destroyed or lost overboard if not properly strengthened and fastened to the transport vessel. The braces installed between the vessel and the crane are called sea fastenings, and any braces or strengthening internal to the crane (not connecting to the vessel) is called voyage bracing.
Casper, Phillips & Associates has over 20 years experience designing the voyage fastening and bracing for shipping cranes and large material handling equipment. Over 30 years ago Bill Casper, the founder of CP&A, designed the sea-fastenings and voyage bracing for the first ocean transport of a fully erected container crane. Recently we designed the sea-fastening and voyage bracing for a large continuous ship unloader. This was the first successful ocean shipment of a fully-erected continuous ship unloader.
Much of CP&A's voyage design expertise has also come from lessons learned. Acting as an expert witness for accident investigations, we have directly observed the consequences and damage that can occur if a crane is improperly secured and braced. This puts us in a unique position with an extremely valuable knowledge base.
A common mistake made by many inexperienced designers is to assume the vessel is infinitely rigid. This is simply not true, especially for heavy seas. The vessel will undergo a significant amount of hog (bow & stern down, mid-ships up) and sag (bow & stern up, mid-ships down). If a crane (or cranes) are tied down along the length of the vessel at more than two points, or cranes are tied together (usually up high), when the ship hogs and sags, the crane (or cranes) will act like a strong-back, resisting the hog and sag. This amount of resistance can be large, and usually well in excess of either the crane, its bracing or sea fastenings. Something will fail - bend, break, part, or collapse. This failure can (and often does) lead to successive failures of other crane fastening or bracing components, until there is no more resistance to vessel hog and sag.