Ok so I set out to understand what the last line of text means in survival books. Upon reading my initial interpretation was that when using this skill-book the amount of crew required to repair the hull/sails would be reduced by 1%. (I have already been informed this is a text error artefact and is intended to say -0.1 which would be 10%)
Naturally, I was wondering how powerful this effect was due to the ambiguity in ship knowledge text and set out to test it. I placed it on my usual Niagara set up and went out to tag an AI trader snow.
After he fired upon me once I hit the hull repair. It read as 27/27 crew to repair. I disengaged from the battle and docked up, removed the skill book, changed nothing else, then sailed out and re-tagged the same snow. I let him fire on me once again and hit my repair. This time my repair showed as 15/15. I found this quite odd, as the total number of crew required had decreased significantly.
So I thought maybe the bottom line on survival books was intended to be a malus and just poorly worded to look like a benefit; however, I dont believe this to be the case because in the pvp store there is another book with the same effect called Boatswain Combat Reports which gives me same effect of -0.01 repair crew requirement. So unless this is a bonus only worded the same, or intended as a handicap for elite pvpers at the cost of 150 pvp I would assume there is a negative error somewhere in the coding causing this mod to increase repair crew required.
Perhaps I have misunderstood the calculation used for how much crew is required to repair, perhaps it is based on how much damage has been sustained at the time of hitting "repair hull" ?
In all tests the ship had enough repairs for a full repair. I will run more tests now and post the results.
Whilst on the topic of this effect I would like to make a further comment: boatswain combat reports is objectively inferior to survival handbook; therefore, the only rational reason to run it would be to stack the effect on top of survival handbook to achieve -0.02 sailing crew required (or -20% if text is incorrect). I would argue that given survival books is already considered pretty useless (out of meta) that having another book to exclusively stack with it is probably a little redundant. That said, I also appreciate on larger ships/over gunned vessels it is a niche pick to help reduce the strain of splitting an already overworked crew.