All the Iranians have to do is make some noise about shutting the Strait of Hormuz - even if they can't do it, the insurance companies won't let the shippers transit. Some will take the longer route and I'll bet that many are lining up plan B right now. Perhaps the large short position may just be a hedge against a long position in oil futures. Anyway, whether the book value is 50 or 40, you get a lot of rusty metal for your money. In at 10.48.
To attempt to answer my own question, .... It seems to me that to utilize this route, you hav e one tanker offloading at one side of Bahrain and another loading at the other side, rather than a single tanker transiting the Strait of Hormuz. Ergo, you need more tankers to transport the same amount of oil.