I guess I'm a perfectionist. I want to hit as near to where I aim as possible.
I just tried my own experiment like I suggested above. I was stationary looking at a Medium Modern Composite Freighter(also stationary) from 1500 yards. I set up a zero degree, zero knot, 90 degree AOB and zero gyro angle, just like you would an O'Kane shot. I aimed center ship and fired. Then I added and entered 1/2 knot speed and fired number 2. The first hit exactly dead center of ship. The second hit just near the forward mast. This is about a quarter of the ships length. I don't know off hand how long this boat is, but to me a 1/4 ships length is quite a variance and if you are firing from a longer distance, we could be talking a miss here.
I use the the O'Kane method often, as it does allow for precision targeting and if you take the time to measure speed very accurately and enter that value, you should hit the point at which the boat crosses the lubber line when you fire. I measure speed for at least 12 minutes or longer (3 minutes won't allow much speed detail) and use a calculator to get the fractions of knots. I see two major advantages here.. (1) You can fire, even from long distances of over 3000 yards and hit the target
where you intend. I have found that when firing on an escorted boat, shooting from about 3800 yards allows you the ability to shoot and scoot and the escorts never come close to finding you. (2) Hitting where you aim saves you ordinance because you can hit the juicy parts of the ship, which allows fewer fish to put'm under. As I have said, if you want precision....
This experiment is easy to verify. I used the Sub School artillary mission. Just make sure you dive fast after entering the mission because they WILL be shooting at you.