Resawing thick lumber by hand is not impossible. In fact, it's pretty easy. Using a frame saw rather than a regular hand saw is the key. The frame saw's thin kerf removes far less wood, thereby requiring lefss effort. Don't get me wrong, you'll get a good workout, especially with hardwoods (see bel ow), but it's not a hard as it seems.
In this example I was resawing a piece of 6/4 maple using a 5TPI blade. I've used a 3TPI blade in softer woods with great results, though with the block of maple, I wanted to use a less aggressive blade.
click on any image to enlarge
Plane one face of the board flat to get a reference face. Then, using a marking guage set to the width you want, scribe a line around all four edges. In this case I was cutting a 1/2" board for a box-top.
Start with the stock mounted securely in a bench vise. Using a backsaw make a diagonal kerf-cut for the framesaw to follow. You only need to make a 1-2" deep cut.
One you've made the kerf cut with the back saw, use the framesaw to saw on the diagonal, until you get about 1/2 the way though the board. As long as the blade is tight and straight, tracking the scribed line is fairly easy.>P
Once you've reached the half-way point, take the board out of the vise and flip it 180 degrees. Again, start by making a kerf cut with the back saw.
Continue the cut with the framesaw until you reach the mid-point of the board.
Flip the board end-over-end and repeat the process for the other two corners. In the end you will have made four diagonal cuts, all meeting in the cent er. Depending on how well you tracked the line while sawing, you should get a fairly good surface.
Clean up the left over saw marks with a smoothing plane, and you're all set! (note that picture is taken before I cleaned it up.
Elapsed time: 5 minutes. This would be faster with a more aggressive blade, or a softer wood, though I have no complaints. It's still faster than a bandsaw if you factor in the all time spent in the emergency room reattaching lost digits, limbs.. physical therapy, etc.