The first way is to "round" up all the bombs, the maximum number of bombs you will get at one time is nine, so once you have your nine bombs its pretty easy to gain all your points as long as you don't detonate any! Keeping them close together you can collect the dubloons for points.
The second way is to not bother rounding them up, but just make them crash into each other from the start, it takes a while longer but is just as successful

When and If a whirlpool appears steer your boat away from it in the opposite direction, keeping your finger on the up arrow usually works!, the bombs will automatically be pulled into the whirlpool, be careful as if one is in front of you it might hit you on the way. another dubloon will appear, if its close by try and grab it, as, when you do another bomb will appear and hopefully that will be taken too before the whirl pool disappears.

If a Gold dubloon appears, take your time to grab this, don't take any chance as they are worth 100np. You only need 167 points for the max 1000np.