The little valves described will do the trick if you have an hydraulic failure. Most of the hydraulic davits I have seen move the hook up and down by a block and tackle working in reverse and driven by an hydraulic cylinder. Needless to say, the hook and its load will drop like a stone if the cable breaks, regardless of any fail-safes on the hydraulic side of things. Keeping the cable washed free of salt deposits will help it live a long and happy life. Unfortunately access to the block and tackle assembly can be well nigh impossible without dismantling the davit. A Bertram sportfish of my acquaintance had a new Marquip davit installed on the foredeck. I asked Marquip how to keep the davit healthy as that location gets liberally doused with sea water. Their answer was to put the boom all the way up, the cable all the way out, and squirt a water hose into the top of the boom. YMMV.