Cargo Handling, Hatches and Hull Design
There are number of methods of loading;
- Modern cranes can load 1000-2000 T/hour.
- Conveyor systems can load between 100 and 700T/hour with the modern systems capable of 16000T/ hour; imagine the stresses imposed on the hull structure at these rates!
- Depending on the cargo, cranes are normally used and the rate of discharge is dependent on the size of the bucket and capacity of the crane averaging around 800T/hour.
Once most of the cargo has been discharged, front loaders and bulldozers are lowered into the holds to direct the residue into sizeable mounds for collection by the crane buckets; then manual labor is used to brush out the holds; a dirty and thankless job.
I had just joined a cargo ship in Dublin as fourth engineer in the late 1960’s and she carried molten latex in a couple of tanks, that as far as I can remember was sucked out through pipes to a shore side hopper. Anyway there was a leak in the steam coils and a only the Chief and I were aboard, he volunteered me to go down into the tank and repair the leaking flange. In those days there was no entry permits or breathing sets; so fortified with a large dram of the Chief’s black navy rum, a rope tied around my waist and a roll of ‘clingerite’ jointing, spanners and a hammer I climbed down into the murky interior. Every so often the Chief would holler ‘are you all right there fourth’ that would echo around and make me jump and drop spanners into the goo at my feet. I found the leaking flanges (there were two) and after repairing them I climbed back up to the deck and had a few beers with the Chief. He gave me the night off and I went ashore to a local hop in the Dublin dockside. There I was, dancing away on the floor when I happened to look down at my feet; yep, I had worn my good shoes down the latex tank and the floor was now being covered in sticky elastic strips coming off them! That was my only experience of tanks and once was enough.
Anyway, enough of my ramblings, they will all be in my book; if I ever finish it. The men and, often women who go down the bulker holds to sweep out, must endure terrible conditions; as do the mates when they enter for inspection of the structural members.
We will come to that in a minute, but first let's look at the hatches. Once again my experience of these on cargo ships were limited to ‘McGregor Hatches’ these were on rollers and, when being opened up accordian style against each other, gave access to the cargo hold.
The bulker hatches work on more modern hydraulic actions and are large, ¾ of the width of the ship and about ½ the length of the holds, so you can imagine their size. They have to be large to facilitate the cargo loading and discharge, they also have to be watertight.
The hull comprises of the engine room space, accommodation, bridge, main deck, cargo holds and fo'c'sle.
Basically, the hull is divided into cargo holds by watertight bulkheads, covered as we have seen by the watertight hatches. The holds are ventilated by manual ventilators and fans to prevent dampness and build up of fumes. Below the holds are the double bottoms, and at the lower and upper corners of the holds are triangular ballast tanks known as hoppers; also help prevent cargo shifting.
The bulkers normally have a vertical bulbous bow, above which is the fo’c’sle being raised from the main deck. The windlass mechanism, anchor locker and fore peak tanks are arranged below the fo’c’sle head. Images of hatches, ballast tanks, and hull are shown below.