Just How Accurate Is The Info. In RFB Ship ID Manual?

[Fish40]

I know in RL the info was spotty in some cases, in particular concerning the mastheights of enemy ships. But what about their max. speed? Was this info also sometimes inaccurate, and if so is it reflected in RFB?

The reason I ask is that I tracked a target which turned out to be a Medium Old Tanker. According to a list of "ship lengths" that someone posted over at the UBI forums, as well as the ship ID poster that came with my game, this ship is 113.1m long. I timed the ship crossing the 0 line of the periscope and came up with a speed that was 1k faster than it's listed max speed.

I then used my sonar to get a range. I recorded the distance, and started the clock for three minutes. I then took another reading and used the difference between the two values to get the speed. This time, I came up with 9.4k. This sounded more reasonable, although by eye the ship seemed to be going faster. I plugged this value into the TDC useing the Dick O'kane method of attack.

When the ship crossed the appropriate line of my periscope, I let three fish go (MK14's set to high speed). Useing the camera (can't help it, I like to watch ) I watched as the three fish sailed just astern of the Tanker. What gives? Obviously despite two methods of calculating, the speed was still off And yes, the Outer Doors were already open

So back to the original question: Are the speeds listed accurate? I would guess that since other inaccuracies existed this could be one of them. Don't get me wrong, I love the realistic uncertainty, but I guess we can't take any of the given info as law.