[blueprint2002]

Chevron Gas Turbine Tankers
A recent thread entitled simply “Gas Turbines” mentioned the fate of the half-dozen or so gas turbine ships built in Australia in the mid-seventies, which is the first I heard of the (mostly) untimely end of that boldly innovative experiment. (Unlike the Sealand and Seatrain GT container ships, whose history has been widely reported, and accessible to anyone who might be interested).
Also less known, as far as I am aware, is the history of the five gas turbine powered product tankers built for Chevron, again in the mid-seventies, and employed on the US West coast and Hawaii. About all I am sure of is that all five ships had their control systems upgraded during the mid-nineties, which means that they had already served for around 20 years without needing re-engining. This perhaps means that they were the only successful commercial gas turbine ships (apart from some ferries), and that they went on to give many more years of service.
Does anyone have personal knowledge of the ships, or know of any published record of their history/experience, such as a magazine article or a technical paper? Some points of particular interest include:
a) The fuel used (HFO would likely be the most economical) and whether experience showed this needed to be changed.
b) Average annual running hours of the gas turbines.
c) Average TBO for the GE main gas turbines. Being of the rugged industrial type, this should have been a long time. And which parts needed replacement more often than might have been expected.
d) Experience with the Ruston auxiliary gas turbines. As these were rather highly rated for the auxiliary power demand that one might expect of these ships (about 35000 DWT), low loading and hence high fuel consumption may have resulted.
Thanks in advance.

 

[Thors Twins]

I know of the Chevron GT tankers, never worked on them but did visit and a tour aboard one of them about 15yrs ago (Overseas Integrity):
a) They used diesel oil fuel their entire careers, uncertain if Chevron experimented with HFO or other fuel types
b) An average of 240 running days per year is fairly standard for opex budgeting, perhaps Chevron did this as well.
c) Average TBO for the GE main gas turbines > dont know. The one i toured had both the original main and auxiliary GT's. I dont expect either were 'virgin' except for perhaps, the main rotor and some other robust ancilliaries.

My take-aways from the tour:
1. everywhere you walked in the Engine Room, was on top of a fuel tank.
2. the Engine Room arrangement was not at all typical to that of a steam or motor engine room. The machinery spaces were compartmentalized mostly on a single deck. Imagine if you can, entering the fwd end of the stbd side machinery space, then walk aft past all the machienry. Enter the door to Steering Gear space (very small space), walk over to port then thru door, walk fwd thru port machinery space. Now, the Main GT was above the main machinery space deck and centerline in a modestly spaced and insulated compartment. The Aux GT was in a separate compartment (think it was on the main deck level) located port side.
3. CCR and ECR in same room, in the Accommodation, A-deck
4. There was no SW cooling for any of the machinery. The Funnel and Engine Casing block was essentially one big cooling tower for the Cooling FW.
5. The vessels did not have FW Generators, however the 2 vessels sold to Maritrans, had been retrofitted later on with flash evaps.
6. These vessels were all-electric. Think the main propulsion motor was AC type. The orig operating concept was to have the Aux GT online during port stays for cargo and ballast system operations, then switch over to Main GT for maneuvering and steaming between ports. On the vessel i toured, the Aux GT was not used but only the Main GT for everything. Don't think it was fuel efficient this way.
7. These vessels were an early double hull design.
8. IG came from a dedicated IG generator plant, not GT exhaust.
9. Cargo Pumps were all electric motor-driven, each had the motor on top of main deck.
10. Don't think Chevron ever traded these vessels outside US waters, only between dedicated load/discharge ports with all amenities and services regularly available (bunkers, FW, spares, stores, provisions, misc. services, etc).

Maritrans purchased 2 GT's in the 90's, refitted them for dedicated lightering service at Big Stone, Delaware. The suezmax crude carriers with draft restrictions, brought in west african crude, discharged approx 750k-1M bbls via STS to the GT's which in turn shuttled the oil to the terminals.

 

[blueprint2002]

chevron gt tankers

Many thanks, Thors Twins, for your very detailed and clear response. Sorry I didn't reply earlier: I'd almost given up looking as there had been no response for so long. I do appreciate the time and trouble you have taken.
I have experience of Naval gas turbines, and always remember how little maintenance work they needed, by contrast with the diesels, to say nothing of steam. So it's nice to know that at least one class of commercial GT ships was profitable to run; they'd have been re-engined or scrapped if not.