Some Targets Need 100s of Bomb Strikes!

I understand that the difficulty to accomplish a feat will increase as one progresses. However, at the final spot of a challenge, theres a boat with 5 targets. It took me over 400 bombs to destroy 1 target. I can deal with it but since it took 2 full days to destroy 2 targets, I'm down to the final hours to complete the remaining 3!!!

Any tips/tricks on how to make bombs have more of an impact? Anybody?