For what it is worth what follows here are some personal considerations, observations, thoughts and ideas which might be relevant to the loss of the mv Stellar Daisy, it is not more than that. The basis is the fact that the ship broke up with a loud explosion as was related by the two survivors. The explosive sound was probably caused by the immense forces coming free during the breaking up of the shell and deck plating, these things do not go easy and silently.
During the design phase of a ship the fatigue assessment is an important issue. The object is to try to capture an average value for the entire trading life of a ship, normally about 25 or 27 years; hence a conservative mean SG value of 0.9 is normally selected for this purpose. The specified cargo SG of 0.9 for fatigue assessment is a minimum value. A higher value may be specified by the owner or designer. For crushed iron ore the SG is 2.1 - 2.9. In other words a tanker is not really well suited for the transport of iron core in terms of fatigue. It requires little imagination to see that the stresses upon a hull when originally configured for the carriage of oil will be very different to that experienced with the central holds carrying heavy ore.
Bulk carriers in particular become progressively weaker due to continuous corrosion. In addition, the repetitive cycles of changing loads and the resulting stresses due to hogging, sagging, panting, pounding and vibration all increase fatigue.
Deterioration of ships hull / structure through corrosion, fatigue and damage is identified as a principal factor in the loss of many ships carrying cargo in bulk . Failing to identify such deterioration may lead to sudden and unexpected accidents. Bulk carrier crews may be unaware of the vulnerability of these vessel types. The consequential loss of a ship carrying heavy cargo can be expected to be very rapid, should a major failure occur.
Solas Chapter XI-1, requires bulk carriers to comply with the enhanced survey programme (ESP) of inspections, including regular inspection of the cargo hold by ship's personnel. However, owing to the time constraints in port, ships' manning levels and charterers' requirements, it is recognised that this may not always be feasible as this is an enormous task time consuming job, due to the size of the ship and that under dangerous circumstances. For instance center and especially wing tanks should be (force) ventilated for such inspections. Also a trained eye is required. The crew members carrying out such inspections must know exactly what to look for and which places are critical.
The conversion of a crude oil carrier into a ship designed to carry iron ore at the same draught is a huge operation with literally miles of welding and several thousand tonnes of new steel to be incorporated. Welding new steel to old steel is not easy and has to be carried out in a specific way. In those days when the conversions took place all first tier yards were filled up with work and they were not particularly keen to take on a conversion. As a result the conversions were carried out mostly by second tier yards under Korean class supervision which does not have a very good reputation as already argued before.
Also tankers are longitudinally framed, unlike bulkers, which are laterally configured. A tanker has enormous longitudinal strength, but the cutting of huge holes in the weather deck for hatches will require substantial compensation. The new cargo will be carried in what had been the tanker’s centre tanks, with the bottom and sides of these spaces massively reinforced for the piles of heavy ore that will be carried.
The cause of the sinking of the Stellar Daisy may never be known. I am curious about the outcome of the official investigation and especially if the ruling will be adapted to improve the safety of bulk carriers. A repeat of any more conversions from VLCC to VLOC is not to be expected, so much is already clear.
In the mean time also the "International Association of Classifying Societies", IACS, say that they are 'anxious' about the Stellar Daisy loss.
As yet, IACS does not have sufficient confirmed information to comment or in any way speculate on the cause of the vessel's tragic loss, Robert Ashdown, the secretary general of IACS, told Splash.