Summary
YOKOSUKA
SUMMARY
The conclusion reached in this study is that the Port of Yokosuka is a good typhoon haven. Note exceptions below. The primary factors in reaching this conclusion are as follows:
The Port provides shelter from wind and sea due to the surrounding landmasses. Wave action induced by typhoons is negligible in most parts of the Port. Storm surge has a negligible effect.
The extensive experience level and the high degree of competence of Port Services personnel.
The orientation of most of the berths and drydocks with respect to the local topography is good. However, Harbor Master Pier West is exposed and vulnerable during strong winds from the north or northeast and may not be suitable during an approaching tropical cyclone. This is especially true if the ship overhangs past the end of the pier. During Typhoon 26W (Ma-On) in October 2004, an allision involving USS VINCENNES and USS CORONADO occurred when USS VINCENNES snapped mooring lines and was blown from its Harbor Master Berth. As stated in the investigation, “ VINCENNES took the brunt of the typhoon winds due to her exposed location on the west, or downwind side of Harbor Master Pier, without benefit of shielding hills or any masking superstructure.” Naval Meteorology and Oceanography Center records indicate that sustained winds of 63 kt with gusts to 79 kt were occurring at that time. Harbor Master Pier East and Pier #6 can also be impacted by strong winds. Ships tied up at these berths should ensure that all heavy weather preparations are made in advance of a tropical cyclone.
The history of the Port. Conversations with Port Ops, pilots, and other personnel indicate that properly moored U. S. Navy ships at most piers and anchorages do not need to sortie from the Port of Yokosuka during a typhoon. Anchorages A-1, A-10, A-11, A-12, and A-136 have good holding ground and can be used by small Naval ships during tropical cyclones. Note that when sustained winds exceed 30 kt, ships may not be permitted to tie up or depart from the Navy piers and pilots may not be available. Under these conditions, Naval ships entering the Port of Yokosuka will normally be required to go to anchorage.
The only situations in which the Port would not be a good haven is when a very intense typhoon passed within 100 nmi to the northwest or within 50 nmi to the east of Yokosuka.
Aircraft Carriers are an exception to Paragraph 5 above. For conventional aircraft carriers, if a berth shift to Drydock #6 is not feasible, a sortie from Yokosuka is recommended. Nuclear aircraft carriers cannot use Drydock #6. Port authorities suggest that a sortie should take place when Tropical Cyclone Condition of Readiness (TCCOR) III is set for sustained winds of 50 kt or greater, or gusts of 60 kt or greater. If a carrier cannot get underway due to shipyard availability, Piers #12, #8 & #9, or Drydock #6 (conventional carrier) would provide the best protection from winds and seas.
For submarines, note that when Berths #10 and #11 go away in the future, new Berth #13 is not as sheltered and could be vulnerable to strong northerly winds and a higher sea state from an approaching tropical cyclone.
Historically, approximately one of every three tropical cyclones passing within 180 nmi of Yokosuka during the 61-year period 1945-2005 is of at least minimum typhoon strength (greater than or equal to 64 kt) at CPA. Statistically, the frequency of sustained typhoon force winds at Yokosuka is about once every 11 years. It should also be noted that the average storm speed at CPA is relatively high, ranging from 18 kt in August to 35 kt in October.
Source: http://www.nrlmry.navy.mil/port_studies/thh-nc/japan/yokosuka/text/summary.htm
