location of centerline on 36' sailboat

I recently purchasesd a partically finished sailboat that needs to have the rudder and keel attached. Does anyone have an easy method to locate the centerline of the boat? The mold line does not appear to be exactly on the centerline. Any ideas.
Thanks

[gonzo]

Run a string from the bow to the center of the stern. Level the boat and with a plumb bob mark the centerline.

[kudu]

Those cheapie little lazer lights work exceptionally well for that purpose too! Check out harborfreight.com for the prices.