Here are a few things to think about...
1) Lens choices: If the only lens you have is the kit lens that came with the camera (the 18-55mm f/3.5-5.6) then this is going to be more challenging because that lens doesn't collect a lot of light. The EF-S 17-55mm f/2.8 IS USM would be a better choice because it has the f/2.8 focal ratio (the "2.8" means that if you divide the focal length of the lens by the diameter of the lens aperture then the lens diameter divides in to the length 2.8 times. The lower this number is... the bigger the aperture is relative to the length... and that means the lens collects more light (which is good). The f/2.8 lens at 55mm literally collects FOUR TIMES more light than the kit 18-55mm lens at the same 55mm focal length.
2) Metering: Normally the camera does something called "evaluative metering". Imagine you divide your image into a checkerboard with lots of "zones", your camera "meters" each zone independently to determine the overall exposure for the image. The problem with this is that a boat parade at night will mean that most of these zones are black. The camera thinks that the average exposure should have a roughly "middle gray" tonality to it. So it will try to lighten up the image rendering the "black" background a "muddy gray" background (which wont look good) and as a consequence the parts of the boats that actually were brightly lit will end up being severely over-exposed (which also wont look good).
SO... you can change the metering mode either to "spot" metering or at least "center weighted" metering (frankly I'd go with "spot" metering). This means the camera will really only meter a small bit of the middle of the image frame to determine exposure (basically where the decorated boat will be) and will ignore the outer edges of the frame (which should be black because it's nighttime anyway.)
3) Mode dial: If you have a fixed focal ratio zoom (or a non-zoom (aka "prime") lens) then I'd shoot in Aperture value mode (Av on the mode dial) and set the aperture to f/2.8 (assuming it's an f/2.8 zoom lens). The lens will shoot "wide open" to collect as much light as possible and the camera will automatically adjust shutter speed to the fastest speed possible given the poor lighting (e.g. perhaps it'll shoot at 1/60th of a second which isn't very fast but it is fast enough for hand-held photos if you are steady.)
If you have a variable focal ratio lens (such as the 18-55mm f/3.5-5.6 kit lens) then using Av mode wont make sense because the aperture will change depending on the zoom. You can either shoot in "Program" mode -OR- you can shoot in Tv (Time value) mode. "Program" mode will be the EASIEST. Program mode is just like shooting in full "Auto" (Green "A+" box mode) except that full auto locks you out of making changes and Program mode doesn't. That means you can actually change the metering mode when using the 'Program' setting but you can't change the metering mode when using full auto. The camera will automate as much as possible.
You should select ISO and set it to "Auto" which will allow the camera to crank up the ISO when needed (and it will be needed... the camera will probably be taking shots at ISO 6400).
BTW, don't use the flash -- keep that down. The flash is good for subjects that are very close to you -- perhaps 10-15' away. But these boats will be farther than that and the flash wont be able to provide any meaningful boost to the light. If you are taking shots of people (friends who are with you instead of boats) then you can raise the flash for those shots because they'll be close enough for flash to be effective.
If you use Tv mode then you'll need to experiment to find the lowest shutter speed you can mange without having blurred boats due to the movement. 1/60th sec will probably work. You can *try* 1/30th sec but it's possible that all the boats will be just a tiny bit blurred since they are moving and it is very difficult to hold a camera steady for a 1/30th sec shot without having any motion blur caused by your body movement.
Speaking of holding the camera... you'll need to develop some good camera holding technique because your camera will be using perilously slow shutter speeds.
You need to turn your body into a stable / solid platform for holding the camera. That means you slightly widen your stance with your feet (imagine a "boxing" stance) with your body centered between your feet. Do not lean in any direction -- keep the mass of your body centered. Hold your left hand with your left palm facing UP to the sky. Place the camera body on your left hand so that the body is mostly on your left palm and your fingers can touch the lens (so your left fingers can adjust the zoom ring). Your elbows will be tucked in to your stomach and you'll bring your camera up to your eye so that your camera is pressed to your forehead. Now the camera is stable because it is supported from below by your left hand which is braced to your stomach and your stomach is stable because it's centered between your legs -- which are steady because you have a wide stance and it would be hard to knock you over in this nice wide stance. Since you are now in a more solid stance, the camera movement will be minimized and that means YOU can shoot with a longer shutter exposure time and yet not have motion blur when doing hand-held photography at slow shutter speeds.
You can do a "thought experiment" in which you imagine that while you are holding the camera, I am going to put my hand on your camera and try to push it down toward the ground. If you are holding your camera with an "overhand grip" and your arms are out to the side then I am going to win. But if you are holding the camera with an "underhand grip" and your elbows are tucked in to your stomach... then YOU are going to win. In reality it's not other people pulling your camera down that you're worried about... it's gravity. If you have nice solid support from below then it doesn't really take much muscle strength at all to hold the camera steady. But if your arms are out to the sides then it'll be sapping your strength to keep the camera steady.
If this is difficult to imagine, just go to YouTube and search for videos with terms such as "How to hold a DSLR" and you'll probably find a LOT of videos to demonstrate the technique. Joe McNally has a video called "da grip" which also talks about how to hold the camera but works best for camera bodies that have a battery grip attached (he teaches you how to rest the camera body on your shoulder -- which works well for bodies with very big heavy lenses.).
In virtually every video you'll see the theme of using an "underhand grip" and keeping your elbows tucked in. Incidentally if there is something solid that you can lean on (a lamp post, a wall, a railing, etc.) then those are all fair game to make you even steadier.
Tim Campbell
5D III, 5D IV, 60Da
