Looks like a fairly straightforward system. I like the use of
D10s, it is a bit different!
Some thoughts:
1. More examples would be nice, especially for the movement portion. I'm still a little "fuzzy" on the turning mechanics. I like the intertia system in principle, as it makes for a more realistic feel to the game.
2. What type of bases were you planning on using for this game? Round like
BFG or Square like
FA? I ask because the 5-degree arc you list for main weapons seems a bit too fiddly. However, if you go with square bases it gives you the option of using the fixed channel arc from
FA, which I think would be easier.
3. While were on the topic of firing arcs, are you saying that the broadside mounts have a total of 90 degrees of arc (45 degrees left/right of their mounting point) or a total of 45 degrees (22.5 degrees left/right of their mounting point)? This wasn't clear from the description, although I think the 90 degrees of total arc makes more sense, especially with square bases.
4. Final point about fire arcs: It might be limiting to list out only 3 options for locating weapons on ships. While this does simplify things somewhat, I'm worried that this limit might reduce variety too much. As an alternative, you could put in additional arcs/mounting points, or you could just describe the arcs for each specific ship in its description.
5. Critical Hits and Boarding Tables: It seems like a waste to me to use a D100 for these tables, but then only list 7 or 8 results. To me, it seems like it would be more straightforward to make 10 results, and then roll a single
D10 on the table (this would have the advantage of keeping the
D10 as the centerpiece of the system). It is a minor point, though, and using the D100 does make it easier to tweak the likelyhood of specific events with much more granularity....I dunno. Maybe this will grow on me if I played a game or two

.
6. As a general point, not really related to the rules themselves, some basic formatting would help. Things like tables, italics for the quotes, simple MS Paint diagrams for examples, etc. would go a long way towards enhancing understanding.
Overall, your rules look interesting! I look forward to seeing what you come up with for the ship stats.