Sea swim vs Lake swim etc

As far as bottoms go, I change into my regular bike shorts. I do wear my bike shirt under my wetsuit. I tried light padded tri shorts one year and regreted it on the run, had to stop every other mile and get vaseline.

Good Luck

Chris

Can't help you on the swim differences- I always wind up in the lake.  Not on purpose, I just seem to sign up for the lake events.  That being said- I do have an irrational (or rational) fear of sharks.  And guacamole.  However...

I use tri shorts for the entire event.  No issues...

The main difference is the waves, swells, chop, current, breakers that the ocean has.  Lakes can also have waves and chop, but usually don't have the breakers.  Once past the breakers I like the ocean swim.  Definitely get to the race a day or two early so you can practice in the ocean.  Also, if you are prone to sea sickness, large swells may make you sea sick.  Although, I know guys who got sea sick in Town Lake at IMAZ. 

I wear a tri top and tri shorts for the whole IM race.  I also wear a tri top and tri shorts in all my training.  Whatever you do, use the same clothing in training that you plan to wear in the race. 

TJ 

Yep.  Seasick in Town Lake.  It was the first year of IMAZ; a couple years ago.  There was some wind and the lake was a little choppy.  He chummed for fish with his pre-race nutrition after about 10 minutes into the swim.  Really screwed up the rest of his race.  Now, you have to understand he was living in southern, land locked, desert New Mexico.  I was living there also.  There wasn't an open body of water within 100 miles.  All of our swimming was done in the pool.

TJ

I live right near the ocean (as one might figure from my user name )  so I've swam in the ocean a good number of times, including in several triathlons.   

Time wise it all depends on the conditions.  I'm guessing you'll be wearing a wetsuit, so you get whatecer time advantage from that.  You are more buoyant in salt water, but don't count on that helping your time- any advantage there can be more than taken away by the water conditions- between the waves, the currents (including ripcurrents- very dangerous- which pull you out to sea) etc.  Waves in the ocean can be somewhat predictable at times and you can often see what will be a big wave coming when it is a distance away, though that can take some experience.  But I've seen the ocean enough times near where I live to know that the waves aren't predictable at all and do some strange things out there in the ocean, especially when the wind is strong and/or there's a storm somewhere within a couple of thousand miles out to see (yes a hurricane down by the Bahamas can make the ocean at the Jersey Shore not a place anyone should swim in). 

At one sprint I did this year, the ocean was really rough so they were forced to change the swim course.  I'm guessing that it was about 500 yards, which I did in 1:10/yard pace - which I can't do otherwise.  It felt like I was in there forever, but I took a good line and sort of bodysurfed in, letting the waves get me in. 

As far as how to handle the waves, if it's a beach start and there is a big wave or two coming, just wait 30 seconds and let them break before going in if you're concerned.  No sense taking the risk of getting knocked under by the waves (which you need to be prepared for that possibility- just stay calm, you'll be able to come up within seconds and you won't drown from that as long as you relax).  Generally, the worst place is by the breakers- where the waves are crashing.  If you're near there and a wave is coming, just go under it- like do breaststroke under the wave- to get by it.  Once you're past them, at least from what I've seen, it's not too bad.  When you come in, try to take advantage of the waves and sort of bodysurf a bit to move along faster.  If a wave is about to crash as you're coming in and you can't outrun it, to where you can't be knocked under it, then just go face the wave and go under it and come back up, swim some more and outrun the next one.

As far as the salt water, especially try not to drink it.  It's just not a good idea (there is a reason why they say to never drink the sea water if you're stranded out in the ocean).  You're most likely going to swallow some of it, which will make you thirsty, so listen to that.  You may also want to take a drink of water and spit it out to get rid of the salty taste.  Also, really do try to get under a shower/hose when you come out of the water (whatever they have there) as the salt water can bother one's skin. 

A lot of triathlon ocean swims are in protected coves, so some of it may not apply in your case.  In that case, you may have the best of both worlds, depending on the currents.