I found the community manual was main source of info for me starting out and good for tips Also are a couple of other third party manuals with good tips:
SH3 Survival Guide:
http://db.gamefaqs.com/computer/dosw...t_hunter_3.txt
Jason's SH3 Survival Guide (not me, different Jason)
http://edseek.com/archives/2005/05/0...urvival-guide/
Red Devil Fan site (rt. side of page has a couple tutorials and hints)
http://hometown.aol.co.uk/dominicoba...HunterIII.html
Avon Lady's FAQ had some useful info:
http://www.theavonlady.org/thesh3faq/
There are a couple of mods out there that add some tools to the NavMap, and others that alter or add features/info to the Nav map itself. Some of the tools mods are thought to be essential to the manual targetting veterans out there.
Use the search feature on this forum too for any particular question you have, many posts and threads on every topic exist by now on every aspect of the game. The search isn't that efficient though, so if you can't find answers to specific questions, just ask on the forum as a last result (or first result for that matter, but the database gets swelled with the same question over and over again, so its best to search first)
As far as the fixed courses for the AI, you can actually open up a file with the campaign editor to view all of the routes and courses that convoys, single merchants, task forces, etc. will take, so in a sense they are fixed, with a starting point, waypoints, and end destinations. There are just so many though, at the very least hundreds, if not thousands, covering practically every mile of ocean, that its random in the sense that you don't know when and where these routes will be in use at any given point in the game.
And unless you have mods, merchants will run straight courses (until it reaches a waypoint) and will only start to zigzag when you are detected. Even if a uboat is suspected within a close proximity by a destroyer escort and not actually pinpointed where it is yet, the merchant/convoy may start to zigzag even though they don't know exactly where you are.
In the closer in zooms on the NavMap, clicking on a ship will give you a large circle around the ship, I think this is the maximum range for them to spot you under ideal conditions, if they are looking your way, perfect weather, and other factors. I find I can often get halfway into that circle before I'm often detected on average, but it varies greatly.
And any merchant, plane, warship, tugboat, etc. if they spot you will radio your location, so if you see a fishing trawler and don't want to waste your ammo on it (saving it for bigger fish) its best to not let them see you to keep up the element of surprise. I heard someone say they will call in a destroyer only if its within like 25km though, and then it will only go to where your last known location was, and go away quickly if you're not there anymore. Planes seem to me to be sporadic at answering contact reports, I think they have to be within a certain radius to respond like the warships, but I don't know what that radius is.