SXSW brings over 100,000+ people to Austin for a two week festival in March that starts with an Education conference, then a digital/gaming conference, and then a music conference. The film festival is going on over both weeks.
This makes flights and lodging much more expensive than normal so most bachelor parties avoid SXSW.
BUT if you are already booked to come during those weeks, no worries. You will have a blast regardless of what’s going on with SXSW. The way SXSW works is that yes, they will take over most of the bars downtown but only starting at 7pm until 2am. From 7pm until 2am, you can pay around $10-$15 to get into any bar that’s not at capacity for festival attendees – simply look at the entrance of the bar you want to get into and if there’s no line outside, you can walk up to the bouncer and ask if you can pay cover to get in ad hoc.
Before 7pm, all events are pretty much open to the general public with free online RSVPs since those parties are thrown by record labels, magazines, and companies like MTV/Facebook. All the night parties that aren’t at bars work like this too (e.g. MTV will let anyone in who RSVPs on their website to a parking lot they rented out for the week). There is a service that will RSVP to all hundreds of parties for $30 per person (http://rsvpster.com/order/). If you can afford it, I think it’s insurance for you so all of your names are all over town and you can let your eyes/ears help you meander as opposed to having a grand plan built by prior research.
For boat parties that week, honestly, not many people will be on the lake. BUT, if you want to get onto a pretty lake and get drunk with your buddies for a somewhat unique experience, simply book online at http://sparkparties.com/activities/boat-parties/.