Smart mines

One way to represent this:

The entire board is a minefield. Targets get attacked (beam dice?) by 
X number of mines per turn, where X gets smaller the faster the ship 
is moving. 

Perhaps (if cinematic):
Speed 30 = no mines
24-29 = 1 beam dice
19-24 = 2 beam dice
etc. 
1-6 =  5 beam dice
0 (sitting duck) = 6 beam dice

This is a no bookkeeping way to "keep the players fleet moving". If 
they zip around and move quickly (or get in the board and off the 
board), they take very little minefield damage (represents mines not 
having time to concentrate where they are). If they lumber about or 
go slowly, the mines get time to concentrate.

This is an abstraction, but that's a lot of what FT is about - try 
for an effect rather than a specific detailed description of 
mechanism.

Note this doesn't tie you to any particular interpretation of the 
mines attack. You could use other die mechanics other than beam dice. 

Tomb