I think the HP of the whale ship is separate from the HP of your squads, so as long as your squads can fend off small pests it doesn't matter how beat up they get in the process. Something else to keep in mind is that 16 Knights of one type are enough to paint the whale that same color as long as there aren't at least 16 Knights of another type as well.
So, if you aren't doing so already, use your top 16 Slice Knights alongside your top 24 non-Slice Knights.
I set my crew to strongest TP, then replaced my last squad with red girls until the ship went red. I can defeat the pests easy enough, it's just sometimes the giant pest keeps defeating me and sometimes it doesn't. I can't work out what is different between the runs I lose and the ones I win. I worked out if I just do the whale ship until it ends I can buy the necklace if I spend a FG or 2, but if I keep losing rounds randomly I will have to spend more
EDIT: Just took 1 of the strongest allies available and I still lost. Using solar blast on the giant pest doesn't do an awful lot.
EDIT2: Now losing 100% of the time. Seriously pissing me off now.
How strong is your whale ship and what level are you trying to do? When I farmed for the item I cleared final level with around 820k slash ship, but for medals I just farmed 1-4 instead since 100% success is better than having a chance to fail.
My ship is a 856k slashing ship. I got to around 4k medals without much of a problem. Now it seems to have gone massively down hill, and my team is even stronger than when I stared.
only got 5 golds this time
>only
Just how good was your last draw?