Finding the displacement of a object as viewed through water

Are you a frustrated harpoon fisherman? I have spent ages trying to spear fish from the side of a boat. The Maths is not hard -
http://www.physicstutorials.org/home/optics/refraction-of-light/apparent-depth-real-depth" [Broken] gives you the formula but it's hard to work it out on the fly and amidst the excitement of a massive Grey Mullett going past.

 

It's on that link for you to use at your leisure. The formula gives both the new angle and the new height. But, if you know Snell's Law, you should be able to derive it for yourself. At least, their derivation makes easy sense.

I'll get back to my fishing when my future son in law buys a new harpoon to replace the one he chucked over the side by mistake.