When I was in the south seas, the locals had spikes set in logs at the groves for husking, piercing, and opening the inner shell. The spike looked like a big 3-4 inch or so taper pin maybe 10-12 (exposed) inches long, driven in a log base first. To husk it, you lifted the coconut and rammed it onto the spike, working around the coconut, To drain the nut, you hit it moderately in the eye on the tip to poke the eye to get out the fluid, To crack the nut, you drove the nut part onto the spike through that eye and thru so the taper end came out the other side, to split it open.
So, if you have a taper pin, use a hammer to drive it through the eye, drain it, and continue driving it until it comes out the other side, and it will split 4 out of 5 times.
Other wise, I have seen the nut sawn in half crossways with a crosscut saw.
(A heavy bolo-type machete-knife will cut it open, but you have to hit it full force and follow through or the blade will bounce in dangerous ways. A dead-sharp axe might work, but I have never personally tried opening one with an axe.)
