Right now I use a rusty open end wrench, I do not think I have paid much attention to how much force it takes to really crank down on the diamonds. It doesn't seem to me like it takes all that much. A small aluminum one like the one I linked has been something I think about every time I see the rusty one, its just never on my mind when I am off the water.

Edit, what I really want is a stubby ratcheting wrench.