Two serious accidents on Liftable Car Decks of Pure Car Carriers (PCC) have been reported since the beginning of this year as detailed below Accident 1. And Accident 2.
Since they are not concerned with the ships structure, liftable car decks have not usually been surveyed in detail unless specially requested. Only general surveys have been undertaken where damage caused by racking forces has been noted.
Please be advised that as these type of accidents had not previously been experienced up to now, the accidents have been investigated and suitable inspection and counter measures have been developed.

Accident 1.

The supporting bracket part of a Liftable Car Deck was broken and it's adjacent members were cracked.

Accident 2.

The deck plate and transverse web were buckled around the middle of the transverse span, and consequently, the girder strength was much reduced and over all the Liftable Car Deck became very deformed.

Regarding the broken supporting bracket part of the Liftable Car Deck (Accident 1.), it was found by examination, that there had been a notch in the supporting bracket part of the Liftable Car Deck and that the crack had extended from the notch, and consequently, the bracket part finally broke. A pillar part adjacent to the bracket part and a cross part between transverse and girder were also found to be cracked.

Regarding Accident 2., the sea condition when the accident occurred was estimated from the crew's evidence, and a calculation of hull motion was carried out on the basis of this sea condition. As a result of this calculation, it was estimated that about 1.5 G acceleration was exerted on the damaged liftable car deck. Also there was complicated undulation resulting from a typhoon at that time and it is possible that a large inertial force might have loaded the deck in such heavy wave conditions.

(To be continued)
A simulation analysis was carried out examining the process until the deck deformed greatly, and it was found that large deformation occurred around the middle of deck transverse with long spans. (See Figure 1.) It is possible that the buckled deck and buckled transverse web resulted in a sudden reduction in the strength of main members. (See Figure 2.)

Also, it was found that the buckling strength for transverse web was reduced further if the tack welding between the web of transverse and deck plate was cracked or detached. (See Figure 3.)
An instruction for surveyors has been prepared (see attachment) to help prevent the above mentioned type of accidents and in order to identify related damage prior to it becoming a major accident.

Ship's owners and operators are urged to pay special attention to the inspection of liftable Car Decks.

For any questions about the above, please contact:

NIPPON KAIJI KYOKAI (ClassNK)
Survey Department, Administration Center, Head Office
Address: 4-7, Kioi-cho, Chiyoda-ku, Tokyo 102-8567, Japan
Tel.: +81-3-5226-2027 / 2028
Fax: +81-3-5226-2029
E-mail: svd@classnk.or.jp