anchors for moorage

Some friends have a cabin on a very shallow lake so there dock doesn't come out far enough for me to dock my boat to it. I suggested we just make a big cement block attach a rope to it and use that so I don't have to pull it out each night we are there. I would prefer that to putting my boat on the dock anyway.

My question is how much should the cement block weigh so my boat doesn't blow away or into shore? Any suggestions on what people use and what shape works the best? I was thinking around 150 to 200 pounds.

150-200 should be good...but dont use a cement block, use a mushroom shape. after time the mushroom shape anchor will dig its way into the ground and assure that it doesnt move around when your boat pulls on it

An old engine block?

The lake wouldn't allow something like that (engine block). The evironmentalists are out there every other weekend I'm told making sure people don't rip up the reeds along the shore. They were suppose to fix the boat launch but community wasn't allowed to because they didn't want any heavy machinery in the water. It's kind of funny though because for me to get my boat off I have to back the truck into the water so far that my tail pipe is pretty much submerged. You can see this steady stream of black Diesel coming from the tail pipe which isn't a good thing I thinking. So my guess would be no engine block.

Any suggestions on making a mushroom shape?

Dig a hole in your yard the shape of the mushroom top and fill it with quickrete. If you think it would be too hard to pull the concrete up when it dries, use something like saran wrap or trash bags to line the bottom of the hole. Or if you're feeling really lazy, just drop the bag of quickrete into the lake with a rope tied around it or something. It WILL work, but those stupid hippies might not like it.