Then it obviously goes down… you aren’t replacing the lost displacement from the boat with anything.
it all depends on the volume of the rock and surface area of boat.
When the rock is in the boat …the water level in the pool is dependent on weight displacement. when the Rock is in the pool… it is volume displacement.
my answer…
There is not enough information about the rock to determine, but the level WILL NOT RISE (unless it’s never thrown into the water).
think of it this way… if the rock weighs 100lbs and is a one cubic foot block. While the rock is in the boat, the boat will displace 100lbs of water. When the block (rock) is thrown into the pool, it now only has to displace 1 cubic foot of water.
water weighs about 63lbs per cubic foot.
a 100lb block(rock) sitting in a boat would need to displace about 1 1/2 cubic feet of water. That same block thrown into the pool would now only displace 1 cubic foot.
:word: That couldn’t have been said any better.
now seeing the “edited” question… it still cannot be determined.
on the other end of it… (i know you said rock)
if you have a 100lb foam block sitting in the boat… it has to displace 100lbs of water. If that 100lb foam block is thrown into the water it will float and still displace 100lbs of water causing no change in the water level.
Bottom line…it will not RISE, but it could stay the same or drop. I have seen a retarded rock float before, it’s called UB’s Concrete canoe, so a bowl shaped rock could float… but that’s deeper into this i’m sure you ever wanted to get into.
EDIT: after reading the other posts…it’s basically the same as what AlbinoMonkeyRat said originally, with exception to the water ever rising. It still isn’t related to density, but ultimately whether the ‘object’ sinks or floats (which could be determined by shape) or if ‘overboard’ means that it even goes into the water. Or as long as “the rock” isn’t an actor/former WWF wrestler (adam)
assuming the rock sinks in the water of the same pool the boat is setting it… it will drop.
Geesh… now the question is completly different. I give up.
the question didnt change actualy, but i wont explain why just yet
water level drops
Also, Jack is sitting here and he says you’re an idiot. The answer is still unattainable(sp?).
You can still throw the stone on the pool decking instead of the water.
I stand by my answer.
the question is obtainable for very a simple reason
awdrifter - the rock goes in the water 
just say it sinks… if we know it sinks in the same pool that the boat is floating in then we know the answer. I’m trying to rule out a trick question.
The water level still drops because the stone is more dense than the boat.
no trick question, and i said “the rock goes in the water” to avoid people saying “well if you threw it out of the pool, it would sink thru the air” lol
The boat will rise. Thats for damn sure.
Here is a better question to ponder:
If asphat was really white, would they still call it “blacktop”?
I am still having trouble getting on with life because I can’t figure that question out.
only if the top of it is black… proceed with life.
Here is an explanation…
If you tied a balloon to the stone for ballast the balloon would have to be MUCH, MUCH larger than the rock.(therefore displacing more water)
Hopefully that visual will help the physicsally challanged.:biglaugh: (get it?)
But then it really isn’t black, only the top is. So, the question still is there.
I cannot proceed…
IB4WALTERSTARTSCALLINGPPLRETARDED
The water level will definitely change. when the rock comes out of the boat, the water level will drop, then when the rock goes in the water, it will go up a little bit again. I voted the same beacuse it will generally be very close.