I'd say your chances are equal zero.

Have a look at that:
http://www.vae.pl/shiii/070116-01/Log_2.html
It's my lat patrol in my first GWX mission. After being spotted at 1711 I managed to sink 1 of the DD's, and after 15 hours of being severly hunted I got sunk in the morning at 0814 next day.
So I think the best you can do against as many enemies in such shallow waters is to LEARN. Use your hydrophone often, try to understand, what they do and why they do that, and try to last as long, as it's possible.
Nothing will give you better lesson. Good luck!