Three of the principal types of coamings used on weather deck hatches are shown in Figs. 125 to 127 inclusive.

Type 1, Pig. 125 may be said to be the most commonly used and is the type shown in the detail sections in Figs. 122 and 123. Both end and side coamings set on the beam and the decking is stopped against them. The corners are halved, the bottom of the timbers being left square and the top rounded to a radius. In the corner the rabbet is not turned square, but is cut across at an angle at about 45 degrees.

Figure 126 is a large corner detail of the type of coaming shown in detail sections in Fig. 124.

Here, the side coaming consists of a small timber set on top of the principal stringer member. The end coaming is worked from a solid timber. It may or may not set on top of the decking and is dapped into the continuous stringer. The dap shown in the figure is square, but very often it is cut on a bevel as shown in Fig. 127. Here the rabbet is also cut across the corner at an angle of 45 degrees. Note that this coaming is not beveled off on the outer face below the top of the continuous stringer as this would make it very difficult to fit in the dap.

Figure 125. Hatch Corners Type-I.

In type III Fig. 127 the side coaming is worked from a solid timber but is extended past the end coaming to the middle of about the second beam from the hatch beam. The end coaming may or may not be set on top of the decking. It is bevel dapped into the side coaming and rods with nuts on each end are fitted to hold the coamings together at the corners. Large washers are fitted under these nuts. The rabbet is turned square in the corner.

In general, side coamings are set with their inside faces plumb, and the bottom edges must therefore be beveled off where the deck carries a camber. End coamings are set with their inside faces square with the run of the deck. Where the deck carries a camber they must be scribed down to shape. Where the corners are as in Fig. 125 this may be done before the corner cuts are made. In Figs. 126 and 127, since the side coamings are generally the first to be fitted, the end coamings are scribed down after the end cuts are made and extreme care must be taken to scribe off the exact amount to get a proper fit at the ends.

Weather deck hatch coamings may vary in height from 24 to 32 inches, measured from the top of the decking to the top of the coaming, depending upon the class of the vessel and the requirements of the classification society rules under which the vessel is being built. Lower deck hatch coamings are usually made only of sufficient height to receive a proper rabbet for the covers.

Coamings are always rabbeted to receive the hatch covers. While the distance that the rabbet is cut in on the coaming may vary from about 2« to 3« inches its depth must always be exactly the same as the thickness of the covers, which is generally about 3« inches.

The tops of side coamings on all decks are always made parallel with the deck. Tops of end coamings on weather decks are worked with a pitch rising toward the centerline of the ship as shown in Fig. 124, Section B-B. There is no rule for the amount of pitch to be used but it should not as a rule be less than about « inch to the foot. Tops of end coamings of hatches on the lower decks are made without pitch where the deck has no camber.

It is very essential that coamings be securely fastened. Generally they are fastened with large button-headed bolts, close spaced and driven from the top through coaming and beam or fore and after. Below, these bolts are either clinched over rings or fitted with nuts set up on plate washers. The heads on top of the coamings are set in counterbores which are plugged with white pine plugs set in white lead.

Hatch Reinforcing

It is impossible to set the ordinary type of hold stanchions in way of the hatches and some means must be provided for supporting, or reinforcing the deck and hatch framing in this vicinity so that it will safely carry the loads of cargo placed at these points.

In hatches where stringers are provided as in Figs. 123 and 124 it is customary to set quarter pillars at each of the four corners of the hatch, these being placed under the stringers. In hatches where the stringers are under the beams as in Fig. 124 the quarter pillars may be set three or four feet fore and aft of the ends of the hatches, provided, of course that the stringers are made strong enough to carry the additional load due to the longer span. In hatches of the type shown in Fig. 124 the quarter pillars are set directly at the hatch corners. This is also true with the design of hatch framing shown in Fig. 122. Quarter pillars are fitted and fastened in much the same manner as hold stanchions. Additional pillars may also be set under the stringers between the hatches, depending upon the distance from one hatch to the other.

In the type of hatch framing shown in Fig. 122, where there is a total absence of stringers, intermediate pillars must be set at the middle of the trimmer beams as these beams are not strong enough to carry the full cargo load. These pillars axe usually made removable so that they can be taken out of the way when loading or unloading cargo.