I have a large ship worth 49 points.

You kill half of it's health.

How many points did you kill? 24 or 25?

It's health is its combined hull and shield value adjusted by any upgrades. The score you get for it is half rounded down.

"When calculating a score, each player receives half the total squad point value (rounded down) of each enemy large ship whose combined total hull and shields, including any Hull Upgrades or Shield Upgrades, have been reduced to half or below."

Thanks, we couldn't find it in the book about whether it was up or down.

Page 3 of the Tournament Rules in red print, under End of Match.