Most of the yacht clubs have their own launches, which leave from different quays downtown. You can get a water taxi, but it's expensive, and they get very busy at certain times.
If you're taking the ferry, to an elopement, one of the clubhouses, etc. - be sure to plan for the TICKET LINES. Mid-week, it's daycamps and tourists, weekends, it's the whole city. There is only one booth that takes visa, you can't buy your tickets online, and the single automatic ticket dispenser is terrible and only prints one ticket at a time. The best idea is to go a few days before and buy a block of tickets - they are good 'forever', and you can skip lines.
Once you get there, it's easy. Elopements on the picnic grounds under a tree, the beach, even by the fountains on Centre Island - nice gardens. But the ferrying over of guests and party is difficult if the streetcar is late, the line is long, etc. EARLY is better. About 11 things start to heat up.
