While in Plymouth we met up with David who I have to thank for passing on the details of a few web sites that he has found. I have had a brief look and they look interesting. Here is what he says:-
This address is for a comprehensive guide to all engine repair and operating manuals. They are free, but due to abuse have a daily download limit. I supplied several of these. Look also at the other manuals as there are several ones about boat DC electrics and alternators.
I found the next website by chance. Anyone interested in astro nav will appreciate a free almanac for the current year as well as all the sight reduction tables split into manageable degrees of latitude. They are abridged but offer as good an accuracy as is practicable for a small boat.
I also recommend this site as an introduction to astro. I have been gradually ditching my electronics in favour of returning to astro nav. I needed to brush up and this offered a good aide.
Look also at the astro nav sight reduction programme at the bottom of the intro page. I have downloaded this and have tried it as a results checker. Works well and with a bit of experience makes for an easy sight.