Section 5.0
Structural Reinforcements
5.1 BASIC CONSIDERATIONS
Mooring fittings and equipment must be connected to the ship structure in such a way that no failure
will occur under anticipated :tatk and dynamic loadings. Section 4 gives (he recommended minimum
strenglh criteria for the fittings or equipment. For heavy equipment such as winches, the weight of
the equipment and dynamic loads in a seaway must also be taken i_oto account. It is not usually
necessary 10 add tbe static and dynamic loads caused by t he ship's seaway motion to the loads gen-
erated by mooring lines or chains, since the ship v..'ill rarely be subjected to excessive motion while
moored. Nevertheless, once· the static requjrements are met, the foundations of heavy equipment
should be checked for dynamic forces in the same manner as other main and auxiliary machinery.
In selecting fittings from var ious st.andards or vendors, the method of hull attachment must be
carefully considered. Less expensive fittings may requ.ire elaborate bull reinforcements. For example,
some uni\'ersal fairleads do not provide stre.nglh members between the end posts, which results in
very high localized reaction loads on the deck.
Fittings or equipment generally apply tension, compression and shear str esses to tbe deck structure.
These stresses mus[ be added to the hull stresses that may exist while the ship is moored. The longi-
tudinal deck stress may be assumed to correspond to the stress generated by the maximum allowable
still water bending moment. For fillingS in the bow and stern area, this stress may be ignored.
Anotber consideration for equipment and fittings i.1l the mid-body area is tbe stress-raising effect that
any local reinforcements may have on longitudinal strength members. This applies especially to deck
plaling and deck longitudinals of high tensile steel (HTS) where the ends of reinforcing members
may generate fatigue cracking in the primary structure. For this reason, transverse reinforcing members
are strongly preferred over longitudinal reinforcements. Where longitudinal reinforcements cannot
be avoided, the ends of the reinforcing members should be very gradually tapered.Tensile loadings (pull on deck plate) are the most difficult ones to accommodate. If the deck plating
is trun in relation to the member on top and the reinforcement below, the heavy welding required
could cause learing of tbe deck plale. FunJlermore, any misalignment between members above and
below the deck would result in high deck bending stresses. For this reason, deck insert plates should
be provided where the deck plate is thinner than the member welded to it. Another method, especially
suitable for bow and stern area equipment sllch as anchor points for brake bands on mooring winches,
is to lead a tension member through a slot in the deck and connec[ it directly to reinforcing members
below the deck. The deck slot generated by this method can be sealed with collar plafes.
Special attention must be paid to connections of fittings made from steel of higher strength than the
bull steel. If local stresses arc high, and adequate compensation cannot be made using the original
hull steel quality, then local installation of higher strength steel may be necessary.5.2 Mooring Winches
Mooring winches are bolted to foundation.s that are welded to tbe ship's deck. Furt,her details on
the safety a.'ipect.s of deck machinery installation may be found in BS MA-93. The foundation should
be designed so that all parts are accessible and hold-down bolts can be fitted from below. Vertical
members should be positioned close to bolt holes and gencrally span the under-deck longitud.inals
or beams.