Egon is correct. These units don't have the power to utilize down pressure. The weight of the drill stem adds up though. I found myself with the hand on the winch handle most of the time. If a rock gets involved, you have to let it chip away at. Otherwise everything starts taking a beating.
One benefit of this much slower drilling process is it is easy to keep up with shoveling out the cuttings. I was watching a crew with a crappy but real drill rig and the one guy shoveling was getting a workout. He had to help with the stem changes so he did not get to rest then either.
I am dot trying to discourage you at all. There is a certain amount of pride that fuels me when you can get something free. One of the reasons I enjoy sailing.