Fake Fireworks effect for waterscape photography

It was night at 13/11 is my first time to take waterscape photography. Me and my friends are decided to make Gaung in Padang City, West Sumatra as the spot to take some photographs. There is dock in front of i take the picture.

The activity was began at 4 pm and ended at 8pm in my regional time. The giant ship near firmament is my first point of interest at my first sight.

F5.6|1/320sec|ISO2500|49mm

I did not satisfied enough, so I tried to find another object to make my first waterscape photography have three dimensions; foreground,object and background. Thus, i make a rocks as my point interest and leave the giant ship. however I felt my photograph have no something special on it.

F10|25sec|Iso-100|18 mm
Then i was thinking, there is something wrong on my spot besides the day is started let the sun go down to firmament.
Then accidentally, when my camera still capture the moment, i lift it to another angle, i realize, it in the exposure time, then i return it to proper place. i surprised for the result.

F.11|30sec|iso-100|49 mm

For an hour later, after i take some break, due to i cannot have special picture on that my first day. This inspirational accident is appear. oh thanks god, you give me a special idea one more time. I see my friend, turn his lenses forward and backward in exposure time. he does not know what he doing at the time. the picture that he got is the light from the dock formed like a fire work. However, his picture is not sharp enough. then i was thinking how to make the picture is sharp enough besides my picture also have firework effect. I only use Canon 18-55mm|3.5 kit, and of course a tripod. i realize that it is not good enough to make great waterscape picture. then, i decided to take focal length 18 mm and started to find some focus by using manual focus on it. After my eye says the picture on my viewfinder is sharp enough, I turned my focal length to 55 mm and in this moment, the picture is very blurred. just let it be like that. then i calculate the exposure as the result, my exposure that i decided such as: F13/30sec/ISO160. On shooting type, i uses timer: i does not have remote shutter. Then, when my camera sensor is burning on the exposure time, i turn the focal length that already on 55 mm ; the picture is blurred to 18 mm; the picture is sharp, slowly. then just left the rest to my camera.
and for the result, i does not disappointed my waterscape photograph have fireworks effect and it also sharp enough.