Then he trod on the poisonous dorsal fin of a cobbler fish lurking in shallow weeds as he launched his board off Perth. The prospect of the former world No 1's 16-year elite level career finishing without attending an Olympics flashed before him. However, with the help of antibiotics, Tobin battled through the initial pain to finish fifth, one place ahead of Ashley.
That secured him the London nod from Yachting New Zealand and the New Zealand Olympic Committee.
"At the time, it [the injury] was frustrating but I had to keep going and the results underlined the form I was in. I'm sure it was a tough decision for the selectors but we had regattas where we had to tick certain boxes and they obviously believed the results.
"The upsetting thing [about the injury] was I didn't actually have a scheduled training. I was just after a light sail before the competition. I pushed off and, bang, the pain was immense. In fact, at one point in the hospital, I passed out. It gave me a bit of grief during the regatta but it was either that, or withdraw to get them cut out. In normal circumstances, I wouldn't have continued. It was nasty for a week afterwards but has settled down. If I get a chance, I'm going to get it cut out after the world championships when I've got a two-week window off training. I can still run and cycle on the foot in the meantime."
Tobin's long-term plan has paid dividends. His overall programme is organised by respected coach Chris Pilone, who was behind Hamish Carter's gold medal at Athens.
Former rival McIntosh advises Tobin on tactics and technique as part of an overall commitment to coaching Dutchman Dorian van Rijsselberge, who won the pre-Olympic regatta and world championships. Tobin works within their unit.
"Coming away with a first and fifth from the [all classes] world championships is a sound result and a credit to the programme we've got in place.
"It's by far the best programme I've had; I've never felt better. The next step is for Dorian to arrive [in New Zealand] and we will do a spell of endurance training [cycling, running and kayaking] to build a base fitness."
Van Rijsselberge's arrival will see Tobin repay a few favours.
As one of the Netherlands' top Olympic medal contenders, the Dutchman received funds to help with accommodation and living expenses at the Games sailing venue in Weymouth. As van Rijsselberge's training partner, Tobin stayed with him.
"Weymouth has become like a home town, I spent at least 90 days there last year. As I see it, local knowledge will be vital."
Speculating on the weather six months out from the Games is a flawed science but sailing off the Dorset coast is generally expected to deliver stiffer breezes than the tame climes of Qingdao, sailing venue for the Beijing Games. It should mean New Zealanders strike more familiar racing conditions.
What if that means Tobin and van Rijsselberge end up racing for gold in the medal race?
"If that's the case, we've done our job," Tobin says diplomatically. "The only way I've found to get ahead in the sport is to compete in training against someone of similar ability. You need others to push you."