The boat on the davits is not a lifeboat as such - it's an 'emergency cutter', kept permanently swung out and uncovered for use if, for instance, somebody fell overboard. There were two of these, one on each side of the ship. They could of course be used as lifeboats, in which case the two collapsibles stored on deck alongside them could be lowered from the same davits. Given time, two more collapsibles stored on the roof of the officers' quarters could then be lowered, again from the same davits. This last possibility turned out to be wishful thinking. Of course it would have been more convenient and certainly quicker for the lowering to have a separate set of davits for every boat but the four collapsibles wre something of an afterthought, not required by regulations and it was never envisaged that they would ever be needed.