[Fr. Frank]

there are two good methods of securely blocking the hull.

First method is most secure: use two sets of keel blocks, one at the transom, and one about 2/3 of the way forward, with 95% of the boat's weight should rest on keel blocks. You also need two boat-stands at about the mid-point of the hull, although placing the stands anywhere between the sets of keel blocks will work.

Second method is most common with hulls under 30': Called a tripod set, there is one set of keel block at the point of keel-rise to the bow, usually between 1/2 and 2/3 of the way forward from the stern. This block needs to be placed so as to support at least 10" of keel. the hull is then balanced by two hull supports at the aftermost corners of the hull at the hard chine.

I use a single concrete block turned on its side with a 2"x10" board across it for the forward keel block, then 3 concrete blocks at each aft corner with a 2"x10" on top of them, and then a 2"x4" piece on top of that running fore and aft.
On my 20' Seafari that gives me a slight rise from stern to bow allowing the hull to drain when out in the weather, and keeps the hull low to the ground in case something should happen. When I crawl under the hull to paint or work on it, I add a brace or boat stand to each side amidships for extra safety.