We put a hole in our boat once. To fiberglass you must lay new material against a hard surface. A crack through the hull once cleaned up will be a hole once it is ground back to sound material. Unless you can get access to both sides with the engine in place, you in my opinion need to pull the engine to build a solid surface to work against. Perhaps a there is a way to place backing without removing the engine a good fiberglass shop would know what is required. A bad patch in rough water might fail.
