It is possible (if one has a full keel boat) to obtain a set of "legs" to allow one to work on the boat between tides w/o so much risk associated with careening. Our boat, a SS Crocker design, has a relatively wide/flat keel (ranging from 9" in the front to 14" wide in the back) and while it did not come with the legs, we know another Crocker with a similar keel did have them and used them notably when they grounded by accident once. Further, we know of a similarly keeled boat that grounded on a large rock in an uncharted area of Labrador in the 1960's and they actually were able to just wait out the tides because they settled nicely onto the wide, flat keel (thank goodness!) atop the rock. I've seen a pic of it and that grounding did look precarious, though, and I'd have been happy to have some boat legs to assist!
Such boat legs are usually attached to the boat's chain plates, can be made of wood, steel, or aluminum, and are stayed fore and aft as well. Some boats have one set of legs, others two. Here is a link to one company that markets such legs: LINK