The present invention relates to a stiffener structure for the top plate of a hatch cover employed aboard a cargo ship, said structure comprising one or a greater number of mutually parallel, elongated, bent steel sections which is/are attached essentially by its/their entire length to the underside of the top plate of the hatch cover.

To strengthen the wide-area hatch covers of cargo ships and to increase the stiffness of their top plates, stiffening structures are required that today are conventionally made from mutually parallel aligned L-sections attached by weld¬ ing to the underside of the hatch cover top plate. Each L-section is welded from both side edges of its one flange to the underside of the hatch cover top plate. Such L-sections require a great amount of surface treatment including blasting, coating and welding. Moreover, the inner angle (90°) of the L-section tends to gather dirt and other debris thus causing an increased risk of corrosion.

It is an object of the present invention to provide a novel type of stiffener section capable of overcoming or at least diminishing the above-described drawbacks. The stiffener structure according to the invention for a hatch cover is characterized in that the bent steel sections are attached by their two longitudinal sides to the underside of the top plate of the hatch cover, whereby the steel section and the hatch cover top plate together form a closed box section.

A preferred embodiment of the invention is characterized in that said steel section has two longitudinal side flanges, both inclined with respect to the underside of the hatch cover top plate as to form with the top plate an angle not smaller than 30° and not larger than 90° so that said side flanges are convergent with each other toward the apex of

the section pointing downward away from the underside of the hatch cover top plate.

Another preferred embodiment of the invention is character- ized in that the angles of said side flanges with respect to the underside of the hatch cover top plate are unequal.

Still another preferred embodiment of the invention is characterized in that between said side flanges, the apex- forming edges thereof, is adapted an essentially planar lower web which is aligned essentially parallel with respect to the underside of the hatch cover top plate.

By virtue of the present invention, the finishing opera- tions of the stiffener structure are reduced and signifi¬ cantly eased over those required by a conventional structure. A single "trough"-shaped steel section replaces two conventionally used L-sections. Hence, the length of seams to be v/elded is halvec ¹ with respect to the prior art. And further, the structure is free from points tending to gather dirt or subject to corrosion.

In the following, the invention is examined in greater detail with reference to the appended drawings, in which:

Figure 1 shows a portion of a hatch cover top plate strengthened with conventional stiffeners;

Figure 2 shows the conventional structure of Fig. 1 in an end view of the hatch cover;

Figure 3 shows a stiffener structure according to the invention in a similar view with that of Fig. 1;

Figure 4 shows the structure of Fig. 3 in an end view of the hatch cover;

Figure 5 shows another stiffener structure according to the invention in a view similar to that of Figs. 1 and 3;

Figure 6 shows the structure of Fig. 5 in an end view of the hatch cover;

Referring to Figs. 1 and 2, a conventional embodiment is shown for stiffening the top plate 1 of a hatch cover. To the underside of the hatch cover top plate, advantageously by welding, are attached elongated, mutually parallel aligned L-shaped steel sections 2. As is evident from Figs. 1 and 2, the L-sections are placed so that the wider flange of the L-section will be aligned essentially verti¬ cally, whereby the narrower flange will be situated essentially horizontally. The weld seams are made to the sides of the wider flange of the L-section that rests against the underside of the top plate as is particularly shown in Fig. 2.

Referring to Figs. 3 and 4, a preferred embodiment of the invention is shown therein having the stiffeners comprised by steel sections 3 formed into an essentially trough- shaped section with two side flanges 4 and a lower web 5. Hence, the shaped steel sections, which are attached at the upper edges of the side flanges 4 to the underside of the hatch cover top plate 1, together with the top plate form a closed box section structure. The angles of the side flanges with respect to the underside of the hatch cover top plate are arranged such that advantageously the side flanges 4 are convergent with each other toward the apex of the section pointing downward away from the underside of the hatch cover top plate 1. The angle of the side flange to the top plate can be made, e.g., not smaller than 30° and not larger than 90°. Also other angles are possible while not particularly practical due to greater tendency of other angles to gather dirt, which is just the opposite of the goal of the invention. While advantageously equal, the

angles of the side flanges to the top plate underside need not necessarily be equal, but instead, the angles can be made unequal at, e.g., 80° and 60°. Such slanted side flanges 4 give an additional benefit therein that the weld seam is easy to make between the edge of the side flange 4 and the top plate underside as a suitable wedge-shaped groove is thus advantageously formed between these elements (Fig. 4).

In the exemplifying embodiment of Figs. 3 and 4, the side flanges 4 are bridged by an essentially planar lower web 5 which is aligned essentially parallel with respect to the underside of the hatch cover top plate. By contrast, the embodiment shown in Figs. 5 and 6, this web is omitted al- lowing the side flanges to join essentially perpendicular¬ ly, whereby a V-section is formed. The apex angle of the V is in the range 60-120°, advantageously approx. 90°.

The maximum height oL the t>Leel section according to the invention is in the range 100-300 mm, whereby the maximum width of the section is in the range 300-600 mm and the material thickness is advantageously in the range 4-6 mm.

To those versed in the art it is obvious that the invention is not limited to the embodiments described above. Thence, while the material of the stiffener section is advanta¬ geously of a ship steel grade, other steel grades can as well be used when permitted by shipbuilding regulations.