Hiding under freighters

I have a scenario where I try and sneak into a port by hiding under a freighter yet the helicopters flying over head seem to be able to pick me out to the point where I feel like I'm wearing a sign saying: "Hey Shoot Here".

So how do you do you manage to sneak into a heavily defended shallow port an not be seen? Is there anything still out there that discusses shallow water operations? And what is the best boat to use (within SCU) for these types of operations?