"People think only geriatric trainspotters go on these trips," she tells her younger companion.
True, most of the 430 people on the triple-deck ferry are not likely to be asked for ID at the bar. But there are clusters of twentysomethings and parents with toddlers who still have their sea legs. As for trainspotters, there's not an anorak in sight.
"We are not avid rail fans," tour escort John Chamberlin explains later.
"We are essentially tourists travelling around the country to see things, using rail as the prime means of transport wherever possible."
The annual Waves and Wheels excursion is one of the more ambitious activities the society runs to help to fund projects such as the Glenbrook railway expansion.
Our destination is Opua in the Bay of Islands and the speed of the Superflyte allows a greatest-hits tour of the Hauraki Gulf and Northland coast: Tiritiri-Matangi, Mahurangi Harbour, Kawau, Goat Island, the Mokohinaus, Whangarei Heads, the Tutukaka Coast and the Poor Knights.
"It's a good opportunity for people to see things they wouldn't otherwise ever see," says Chamberlin.
"Ninety-five per cent of people would never otherwise see the Poor Knights."
As we're admiring the sheer volcanic rock forms and pohutukawa forest on these marine and conservation reserves, 430 more travellers are making for Whangarei by train.
That's as far north as Toll Rail will allow passenger trains. Coaches will bridge the gap between Opua and Whangarei before we swap transport modes for the return to Auckland.
It's quite a logistical exercise and Chamberlin warns us to expect the unexpected.
Last year's trip went no further than Whangarei after the sea got up. There seems little chance of that on this brilliant summer's day. But as the sun gains strength, so does the wind and a rolling swell, generated by a distant tropical cyclone.
It sets off a domino effect, and the St John staff are soon busy handing out sickbags. I'm contemplating a beer but decide to wait.
Fullers' Captain Peter Brough proves a knowledgeable and sympathetic guide. As we pass the skeletal remains of the Rewa, sunk to provide a breakwater off Moturekareka Island, he scowls, "Waste of a good ship".
At the Poor Knights, we cruise within 50m of a popular snorkelling cave, big enough for launches to enter but too small, surely, for our ferry.
"You can take the boat in until the top of the cave is in line with the wheelhouse," says Captain Brough.
Watching the vessel's rise and fall against the volcanic cliff face, I'm relieved he's not going to try that today.
By now he has heard from the sick bay that two passengers have more than just mild seasickness and decides to head straight for Opua. We miss little, passing close enough to the Hole in the Rock off Cape Brett to say we've been there.
An ambulance is waiting at the wharf for our sick passengers while the rest of us board one of nine coaches for the one-hour road trip to Whangarei. It seems a pity: Marcus Lush got as far as Opua by rail (albeit by jigger for the last bit) - why can't we?
The unkempt Whangarei railway station is another sign of passenger rail's Cinderella status. The journey ahead will only highlight the potential tourism gone begging.
Our nine-carriage train hauled by twin diesel engines is an attraction in itself. We skirt the upper reaches of the Whangarei Harbour, crossing mangrove swamps and wetlands, the tide lapping at the tracks.
We cross the Waipu dairying flats, startling the cockies more than the cows. We pry into farmers' backyards. A weekend 21st is winding up beneath a marquee; a corral of Holdens betrays a few afternoon quiets.
Soon, we leave civilisation behind, skirting the Brynderwyns through totara, nikau and cabbage trees. The line here used to carry kauri and kauri gum. The gradient is steeper, the curves tighter, and the heat on the lines means the train has to slow to 40km/h.
Chamberlin keeps us vaguely in touch.
"We've just been through the former settlement of Paparoa," he says, as we pass a couple of ramshackle houses.
"We're a bit behind schedule."
Then, in the middle of nowhere, we stop. The train manager is on the phone to Wellington; he needs a track warrant before we can proceed. It seems train control in Wellington has no way of monitoring our progress so we have to call every so often to ensure the line ahead is clear.
We'll need another warrant at Maungaturoto. At Kaiwaka, a message comes over the loudspeaker: "If anyone has seen the train manager's telephone could they bring it to Car A."
At Wellsford, where we stop for a barbecue dinner - steak and sausies for 430 - one of our ill passengers from the ferry is waiting. He has discharged himself from Whangarei Hospital and come by taxi.
The line from Wellsford to Helensville is billed as the scenic highlight of the journey, skirting the Kaipara Harbour and cutting through dense bush and wetlands. Unfortunately, the time we've lost means we miss much of it. We reach Auckland an hour late at 11 pm.
We later learn that those who returned by ferry had their misadventures too. Two seasick passengers were airlifted off near Whangarei.
"When you get nearly 900 people onboard a boat, people are seasick," says Chamberlin.
The four who got very ill should not really have been aboard - all had been in hospital in the last few months for serious operations. They had not heeded the warning in the publicity: "You must be reasonably healthy and physically able to take a sea voyage. If unsure, please seek advice."
Chamberlin is the organisational brains behind the society's growing array of excursions, though he insists none would be possible without the hard-working volunteers.
Other day trips include Mt Maunganui, Kawau Island and the Kaipara Flats. A 15-day tour of the South Island is planned for October. Overseas destinations this year (sorry, they're booked out) include a 20-day rail tour of Canada and the US and a 21-day tour of Scandinavian fiords, Denmark and Germany.
Next year's schedule includes the scenic railways and fishing villages of Devon and Cornwall before heading north to the Scottish Highlands.
The semi-retired Chamberlin has found his experience as a corporate tax consulting partner at Deloittes readily transferable to the role of tour organiser.
"You chop out the middle man and you can get some very good rates. When you ring up a service provider and tell them you've got a party of 50 it can be very attractive.
"I get my kicks out of seeing something I put together run smoothly and people enjoying themselves. That's very satisfying."
Chamberlin admits there is an element of risk in the society's excursions, but the passengers are not the sort to demand a refund if things don't go to schedule.
"It's not the sort of thing a commercial organisation would touch. We can tackle it because we're all volunteers.
"You have to be flexible - there may be changes along the way."
CHECKLIST
Further information: See railfan.org.nz or ring (09) 636 9361 or 0800 472 453.
