# Thread: Estimate speed via wake size... How? | Forums

1. I've no clue how to estimate speed via wake size, could some one please explain this with some more details along with when and when not to try this...

2. I've no clue how to estimate speed via wake size, could some one please explain this with some more details along with when and when not to try this...

3. Wake is the water that is pushed away from the bow when driving a ship. It is the white spraying water in the bow(front end) of the ship. It's real easy, Bigger Bow wake=More speed, and vice versa. If you are going to torp a ship that you see is gong fast guess the speed and then you divides the ship top speed with 2, Example (top speed of 10 knots divedes by 2 = 5 knots, estimated speed by you 7 knots and then take the number most to the middle, in this case 6 knots. DONE!

/GS

4. Easiest thing to do is to calculate it yourself. No really, it's EASY.

Put a mark at the front of a target with the pen. Start the stopwatch. At 3 minutes 15 seconds put another mark at the front of the same ship.

Now, provided you are in METERS, use the ruler to draw a line between the two marks.

The resulting number is their speed in knots. SO, of they have gone 900 meters (or .9 km) their speed is 9 knots. If they have gone 1.2 km, their speed is 12 knots. VERY VERY simple and takes but 3 min 15 seconds of plotting.

5. Put a mark every minute, multiply distance measured by compasses by 60 - 0.1 miles = 6kts, 0.2 miles = 12 kts.... midway between 0.1 and 0.2 points = 9kts, and so on. Easy to get within 1-2 kts, then let your solution run for a minute to check the target and your torp solution don't move at different speeds... if the target lags the solution your speed needs winding back a knot or two, if the target moves faster then add a knot or two.

This is the imperial measurement version

6. I believe the wake is the wave left behind the vessel. The spray in the front is just that, bow spray. When you go past a marina you'll see signs that say.."watch your wake" because they rock the docked boats violently.
Displacement hulls make larger wakes in relation to thier speed. But a vessel with a larger displacement could generate a larger wake going slower then one of less displacement going faster.

7. Thx... but ehmmm I'm not quite following you, on how you calculate things.

I understand the part about ship speed and bow wake size. Slow going ship, small wake. Fast going ship, big wake.

Taking the top speed of the ship and dividing it by 2. Sure, if you say so... But why divide it by 2?

Then you give an example, what I don't understand... Might be a good example, but I don't see where your going with it nor do I see any logic in it.

So ehmmm, that leaves me back to square one.
Can you estimate the ships speed by just looking at the wake size?
Or do I first need to calculate the ships speed in knots by doing some drawing and measuring like how psychp0 or davejb1167 explain things... Then have a good long look at the wake size and recall it from memory the next time I encounter a ship with a similar wake size...

More details, please... want to learn more, but the given replies don't make sense to me and how the are linked to wake size.

FYI I'm not using the metric system.

8. I don't know how to do this in game, but the reason wake size and speed are related has nothing to do with the size of the ship. The rate that a wave propagates in water is fixed. Thus, a stationary boat emits a ring, which can be thought of as a 180 degree wake, a boat moving at a speed greater than zero leaves behind the characteristic V, the narrower the V the more water the boat has moved through in the same period of time, following that model, a boat moving at infinite speed leaves a single line behind it. Thus if you know the right constants, which i don't, you can calculate speed based on the angle of the wake.

9. I have the collectors edition of the game with the separate recognition manual. It states the length of all ships.

I simply use a stopwatch to see how much time a ship uses to pass through my crosshairs (target lock off). The closer you are to 90 degrees AOB, the easier the measurement is (but it works quite well at AOB as low as 50-60 degrees). Then you divide the length of the ship with the time it takes to run a length; which gives you meters per second which you can multiply by 2 to get a rough estimate in knots, or you can multiply with 1.94 to get it REAL accurate (not really necessary).

Example: A Takao heavy cruiser passes through your sights in 20 seconds. It's 204.5 meters long. 204.5 meters / 20 seconds = 10.2 m/s. Multiplied by two, you can easily see the speed is roughly 20 knots, or you can do it the more complicated way: 10.2 X 1.94 = 19.8 knots.

Using this technique, I've hit almost every target with manual TDC at distances up to 2000 meters. Works like a charm, and you don't have to use map contact updates. Also, on known ship classes with known length, this would work quite well in real life too. I don't know how the skippers in WW2 did it, but this works quite well for me

This process requires a handheld stopwatch (because the ingame watch resets when you stop it, making it too difficult to use for this in my opinion, a simple calculator, and the recognition manual that tells you the length of the ships.

Hope it helps

TO devs, mods, or whoever capable of doing this: The length of ships should be stated in the in-game recognition manual, and the manual should not reset to the first boat in the list every time you close and open it.

EDIT: I just noticed that you mentioned not using the metric system, but the conversions are quite simple. 1 foot = 0.304 meter and 1 nautical mile = 1852 meters. Knots = feet per sec / 1.69.

HOWEVER, you don't have to play the game in metric to use my method even though the recognition manual uses metric units. The math is still correct even if you play the game in cubits, feet, furlongs, yards or whatever you fancy . I find the "multiply by two"-method easier than the "divide by 1.69".

10. Also, if you don't have the printed recognition manual, I'm sure someone crazy could be persuaded to write down the length for all ships in the game. I could, but not now as it is late where I am.

Good hunting

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