From the manual :
"Using too many loops
This is rarer, but using too many loops like For, For Each and Repeat can cause the game to slow down. Nested loops are especially likely to cause this. To test if this is the problem, try temporarily disabling the looping events."
I don't think this for each loop is going to affect the performance, it's more likely going to be the number of ships you have loaded in memory. You can check if it is having an effect using the debug mode. Since you are updating variables here and not, i.e. the size of the ship or lots of textures at once, I don't think it's going to matter for performance.