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Yokohama Maru Dive Report
by Ian Williams

The Yokohama Maru was a 300 foot Japanese supply ship that was sunk in 1943 (44?) in the Salamaua area of Papua New Guinea. The wreck lies in very deep water and can only be visited by divers experienced in deep water operations.

The wreck sits in an upright position on the sea floor with the upper deck in 194 feet of water. The ship is in very good condition and is structurally sound. The vessel has three main cargo holds and a number of intact superstructure davits.

Black coral trees, red gorgoneion fans and white sea whips have grown on the superstructure, while the outside of the ship is covered in soft corals, anemones and other invertebrates. Surprisingly, there were few fish at the site, although I have been told that tiger sharks occasionally patrol past the wreck.

Penetration dives can be made into either of the cargo holds, however, a flashlight is needed. Diving in the holds requires great care as a thick layer of silt has accumulated on the bottom. If the silt is disturbed it can reduce visibility to zero causing disorientation, this in association with nitrogen narcosis, and a limited air supply can be fatal to inexperienced divers.

The vessel carried supples vital to the Japanese war effort and each cargo hold has an assortment of military hardware. Small trucks and motorcycles occupy one hold, whilst various calibre munitions can be found in the second hold. Brass timing fuses are to be found littering the deck, along with small calibre ammunition and other items such as davits, cranes and winches.

The Dive
The maximum bottom time allowable for a dive to 194 feet is 8 minutes, therefore, a quick decent to the upper deck of the wreck was critical, and diver propulsion vehicles (DPV or scooters) were used to minimise the decent time. As I reached the deck I felt mild euphoria, a result of the fast decent and nitrogen narcosis. The black coral trees that hung from the wreck's superstructure, combined with the limited light at this depth, created an errie gloom as I explored the wreck's deck.

I scooted over the deck beneath the davits and superstructure and over a large black cavernous hole which was cargo hold number one. An assortment of vehicles could be seen jumbled inside the hold. A small tank, barely visible in the darkness was identified by its tracks and turret, in addition to a grader and several dozen rows of tyres.

Skimming above the deck on the scooter it is surprising what can be seen in eight minutes. The deck was littered with metallic rubbish. Nothing had been removed; it was as when the ship sunk fifty odd years ago. The second hold loomed beneath and several pallets of large calibre munitions could be seen. A thick blanket of silt covered much of the shells, it was evident that the cargo hold was stacked full of shells of various sizes.

A long ascent awaited me. The scooter was tied to a decompression line and I began a slow ascent. To spend eight minutes at 194 feet required me to spend 63 minutes ascending and decompressing with a tank change at 60 feet. The last 22 minutes being spent breathing 100% oxygen. The oxygen although not necessary, was an added safety measure as PNG is very remote and a diving accident or illness would have proved very problematic.

Many underwater wrecks lie in Papua New Guinea waters. Several have been discovered and are dived regularly, but many await discovery.

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