The game was designed to run at 30fps, and when you "lock" a framerate in most video card apps, that is just a "cap", but does not restrict the game to just that framerate. If you are crashing with only large convoys, then you might be running out of memory. This would include not enough RAM to begin with (4Gig recommended minimum), or hard drive space (7200rpm drive with about 1/2 of its space free recommended), or possibly the 4Gig Patch or LAA you used are not properly applied to a write-enabled SH4.exe file. There is also the possibility that if you are crashing only on certain large convoys, that there is a mis-configured ship or airplane involved, either with a "bad" name, or "bad" Type=" line.
