Well I am no expert on this, however, if we think about it, the bow section is really more than just the bow, it is two thirds of the ships length. So around 30,000 tons, plus another 30,000 tons of water, so a 60,000 ton lump of metal falling then it must have been going at a grate speed, however, as the water pressure increased then perhaps that slowed down the decent rate to perhaps 40 mph, according to a study I recently read.