This article thoroughly reviews the state-ofthe-art methods for setting ALARP upper border as a straight line in logarithmic graph, which is the common practice in the risk assessments of nuclear, chemical plants and maritime facilities. It also reviews methods for setting ALARP upper border based on economic importance of a considered ship type. As a result, inconsistency related to ALARP upper border has been identified and new methods to resolve such inconsistency are developed. Here, firstly a method for approximating FN diagrams of existing major ship types is proposed and it is applied to ship types which consist of ships above 100 gross tonnage. After that the approximated FN diagrams were checked by goodness-of-fit test by 5 % significance level, and it was validated that those approximated FN diagrams well express corresponding FN diagrams made from IHSF casualty and ship databases. This method can extrapolate FN diagrams made from those databases to the area of severer accidents with more fatalities, which have not been occurred yet, rationally. Secondly, problems that accompany with an existing method for setting ALARP upper border are discussed and methods for resolving the problems using the approximated FN diagrams are proposed. The methods can set ALARP upper border keeping consistency of ALARP upper border between individual risk and FN diagram. Lastly, the new method for safety analysis of ships using approximated FN diagrams of major ship types is introduced. The method is used in order to find ships' groups which should be considered preferentially. The method for approximating FN diagrams and the method for setting ALARP upper border proposed here is so general that they can be applied to risk analysis of the fields which have a lot of accident records like maritime field, such as aviation or automotive fields.

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In order to preliminary investigate effect of HDS (Highly Ductile Steel) on the crashworthiness of struck ship, a series of large scale 3-dimensional ship-ship collision analysis are carried out using the non-linear finite element code LS-DYNA. A very large crude oil carrier (VLCC) is assumed to collide with midship region of another double hull (D/H) VLCC in right angle (90 deg.). Two collision points for the struck VLCC are assumed. One is between Swash Bulkhead (S.BHD) and Oil Tight Bulkhead (OT.BHD), the other is just on S.BHD. Damage extent and total absorbed energy until oil cargo tank ruptures in the case of HDS are compared with those in the case of conventional material. Critical colliding speed (VB,cr) is also compared. Effects of HDS on absorbed energy and VB,cr are discussed in detail. It can be found energy absorption by inner shell (IS) rupture with using HDS is about 2–3 times larger than that with using conventional It is also estimated that IS rupture does not take place when a striking ship collides in less than 8kt in the case of using HDS although a critical striking velocity in the case of conventional bow is about 4–5kt.

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Summary NGH (Natural Gas Hydrate) FPSO is deemed as one of the attractive solutions for relatively small gas fields. NGH process plant is installed on board FPSO and it produces NGH from raw gas transferred directly from subsea wells through flowlines and risers. For 3 years since 2004, we have been investigating tandem offloading system for NGH FPSO and a shuttle tanker in the south east Asia and Oceania. We evaluated workability of the tandem offloading system for NGH FPSO under combined environmental conditions. As a result, we confirmed that workability under the offloading conditions attained 100% by using a mooring unit that has large restitution force.Based on the aforementioned results, we carried out a safety assessment of the offloading system according to HAZID (Hazard Identification Study) and were awarded AIP (Approval in Principle) by NK. Furthermore, comparison of economical efficiency between NGH Chain and LNG Chain, under the conditions that gas production was between 48 to 275MMscfd, the production period was 30 years, and the destination was Japan, indicated that NGH was advantageous when gas production was 80MMscfd or less.The results of investigation on the tandem offloading system for NGH FPSO are reported in this paper.