Liquid images in flash

I have aquestion with reagards to liquifying images in flash.

I have an image with the boat and I would like to create an illusion of the water movement beneath it.
I have seen it done in java loooong time ago. but now I would like to have it done in flash.

basically I underetsnad that i have to create a mask and animate it. but I do not know how to accomplish this.
the animation should only appear beneath the boat bottom and should loop indefinetly.
I have read kirupa’s tutorial on luquifing an image but coulnd not uuse it since it involves triggerring the animation based on mouse movements. I need automatic upon loading of the flash the animation to start.
thank you