The tanker design process begins by specifying the operating condtions and loading pattens that the ship must be able to handle. It seems self-evident that a ship should be designed to handle all the operating conditions that it could reasonably be expected to face in normal commercial practice with a healthy margin for operator error. Current Class tanker rules use a different philosophy. The ship is designed to handle only the loading conditions in the Loading Manual and then just barely. Just about everything else is implicitly illegal. The yard's job is to make sure these conditions are as narrow as possible to save a bit of steel. Class doesn't seem to care as long as these restrictions show up somewhere in the paper work. This philosophy was taken to particularly ridiculous heights in the case of the one-across tankers where the Mate was given a set of stability restrictions which couldn't in reasonable commercial practice be followed, resulting in a spate of lolling casualties.

We replace steel with restrictions. Don't want to put steel in the bow. No problem, just put a line in the Loading Manual that says the ship can't operate below x meters draft forward, can't operate with the forepeak tank empty, etc. Want to reduce the hogging moment allowable. No problem, tell the crew they can't use all the ballast tanks even when the cargo tanks are empty. Combine that with a restriction on draft forward, and you end up with a tanker which has absolutely no flexibility on the ballast leg. Need to inspect a ballast tank. Forget it. There is only one ballast configuration and it is the one that stresses the structure right up against the limit. Captain wants to get the ship a little deeper in the water in bad weather. Forget it, unless he wants to risk all sorts of problems for violating MARPOL.

When you talk to Class people about this problem, they invariably take the position that "It's not Class's fault. The owner accepted the conditions, so it's his fault." The most damning twist on this argument we know about is the American Bureau of Shipping (ABS) cargo tank density restriction. In 1997, ABS was falling behind in the race to see who could approve the flimsiest ship. The lightweight of a rule minimum ABS VLCC had become 500 to 800 tons more than that of a rule minimum Det Norske Veritas (DNV) or Lloyds Register (LR) VLCC. The owners were all going to LR and DNV in order to save a paltry $25,000 to $50,000 on an 80 million dollar ship. ABS felt it had to do something to "compete". The solution was to change the design liquid density for the purposes of sloshing force calculations in the cargo tanks from 1.025 (sea water) to 0.90. This change was not widely promulgated. Not only did this mean that the owner could not legally load many crudes and heavy petroleum products in his cargo tanks, it meant he couldn't put ballast in any of the cargo tanks including the tank that was labeled gale ballast. Many owners were not even aware of this new restriction.

But when Hellespont raised this with ABS personnel, we actually were given the "if the owner want to put anything heavier in the cargo tanks, he has to tell us" argument. The idea that the owner has to tell class that he wants to be able to put ballast in the gale ballast tank was so patently ridiculous that ABS backed off from this position about 1999. And did something even worse. The 0.90 is now buried in the rules as a "calibration factor". The owner can now legally put sea water in his gale ballast tank, even though the tank is only designed for a 0.9 density liquid.

Another problem with the "owner accepted it" argument is that usually these restrictions don't show up explicitly in the Contract or Spec. The Spec does not say the "forward draft must always be more than x". The Spec says "Trim and Stability will be evaluated for the following conditions". The Owner has to guess what this implies in terms of restrictions before he's even seen any calculations.

The latest twist on this game is the yard's use of the IMO visibility requirement to build a still weaker ship. The yard argues that, since low draft forward would result in a longer than legal blind zone, the structure does not have to be designed for such illegal conditions. Talk about unintended consequences.

Much more basically, blaming the owner for not imposing specifications above class requirements is the same thing as saying, Class have stopped being a regulatory body. Class originally was the creature of the insurers who recognized from hard experience that, left to their own devices, owners would take bad risks and the underwriters were the ones who were going to pay. (The crews paid too but nobody seemed to concerned.) The whole idea of Class or any tanker regulation for that matter is to prevent owners from being imprudent. In the modern world, where more than just insurers and crews pay for owner imprudence, the owners must be regulated. If Class doesn't want to impose reasonable design conditions, somebody else will step in.

The Classification Rules should require:
  1. any transverse combination of cargo tanks across to be empty at or near design draft,
  2. a reasonable range of asymmetric cargo loads at full draft,
  3. all ballast tanks to be 100% full for a full range of bunkers,
  4. the ship to ballast down to a reasonably deep draft without resorting to ballasting cargo tanks.
  5. any single ballast tank to be empty with all the other ballast tanks full,
  6. normal ballast exchange (not flow through) sequence without restriction on weather.
If these reasonable requirements are imposed, you will find that you need a hogging moment allowable of about 1 million ton-m for a standard sized VLCC and a shear force allowable of around 30,000 tons. A rules minimum VLCC will have a hogging moment allowable of 620,000 ton-m and a shear force envelope which maxes out at under 20,000 tons. In other words we need about 50% more bending moment and shear force than Class currently requires. The extra hogging moment will cost about 600 tons ($300,000) and the extra shear force can be obtained largely by making the longitudinal bulkheads HTS (without reducing the thickness) at a cost of about $66,000.