ship stopping distances

i wanted to run some numbers by you to see what is the most realistic ship slowing times in your opinion

i tested the battleship kongo from a 20 kt speed doing evasive manuvers and at a 15 kt speed and it will stop by just turning off its engines and drifting for the stoping test

these are the numbers i got for three different settings i tried:

stopping test one:
from 15 kts - 11 kts = 2 minutes
from 15 kts - 10 kts = 3 minutes 15 seconds
from 15 kts - 9 kts = 6 minutes
from 15kts - 8 kts = 10 minutes 10 seconds
from 15 kts - 7 kts = 15 minutes
from 15 kts - 6 kts = 20 minutes 30 seconds
from 15 kts - 5 kts = 26 minutes 45 seconds

evasive manuvers test: it slows from 20 kts to 10-12 kts when turning

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stopping test two:
from 15 kts - 11 kts = 4 minutes 30 seconds
from 15 kts - 10 kts = 7 minutes
from 15 kts - 9 kts = 10 minutes
from 15 kts - 8 kts = 13 minutes 45 seconds
from 15 kts - 7 kts = 18 minutes 20 seconds
from 15 kts - 6 kts = 24 minutes 15 seconds
from 15 kts - 5 kts = 32 minutes

it slows from 20 kts to 12-14 kts when turning


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stopping test three:
from 15 kts - 11 kts = 4 minutes 30 seconds
from 15 kts - 10 kts = 7 minutes
from 15 kts - 9 kts = 10 minutes
from 15 kts - 8 kts = 13 minutes 45 seconds
from 15 kts - 7 kts = 18 minutes 20 seconds
from 15 kts - 6 kts = 24 minutes 15 seconds
from 15 kts - 5 kts = 32 minutes

it slows from 20 kts to 14-15 kts when turning

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acceleration test for all three versions above:
from 1 kts - 5 kts = 15 seconds
from 1 kts - 10 kts = 1 minute 5 seconds
from 1 kts - 15 kts = 2 minutes 50 seconds
from 1 kts - 17 kts = 4minutes
from 1 kts - 20 kts = 6 minutes 15 seconds


in your opinion, which is the most realistic slowing speed in evasive manuvers and in your opinion, which is the most realistic slowing down speed from turning off engines?

[Rockin Robbins]

Question: is the same set of adjustments going to affect acceleration and deceleration? I would think (non-researched opinion that could be dead wrong) that deceleration would be considerably faster than acceleration. Tater could really help here I think, with some real ship numbers.

I'm thinking a 20 knot ship should go about 15 knots when maneuvering, decelerate like #1 and take over 30 minutes to go from 1 knot to 20 knots. So I would say acceleration like #3 and deceleration like #1. And of course, the limited controls will probably make it impossible!

That's my opinion right now, subject to correction by hard numbers from real surface craft.

Originally Posted by Rockin Robbins

Question: is the same set of adjustments going to affect acceleration and deceleration? I would think (non-researched opinion that could be dead wrong) that deceleration would be considerably faster than acceleration. Tater could really help here I think, with some real ship numbers.

I'm thinking a 20 knot ship should go about 15 knots when maneuvering, decelerate like #1 and take over 30 minutes to go from 1 knot to 20 knots. So I would say acceleration like #3 and deceleration like #1. And of course, the limited controls will probably make it impossible!

That's my opinion right now, subject to correction by hard numbers from real surface craft.

actually no, i CAN control deceleration and acceleration seperately however my test doesnt include reversing engines.

drifting is controlled by one set of values and acceleration has its own value.

as for stopping its like a train, once you get a large mass in motion its a lot harder to stop it quickly power wise than it was to get it in motion.

thats why a train needs brakes on all the cars but only one or two engines to get it going. (an object in motion wants to stay in motion)


EDIT: i also added the acceleration tests i got for all 3 versions above

[Sailor Steve]

On the other hand, a train doesn't have an equal weight of water pushing against it all the time. Ships do decelerate relatively quickly (relative to cars and trains, that is) but the slower the ship is going the less the drag, so it might drop from 15 to 10 knots in a lot less time than it takes to drop from 10 to 5 knots. Funny, that is very much how your tests look.

I think test one is closer to reality, but that's just what I think, not based on any hard facts.

On the other hand, there is no way Kongo is going to accelerate to 5 knots in 15 seconds. Should be more like 5 minutes. To 20 knots should take 30 minutes or more. I'll get some numbers from home and put them up tomorrow.

Originally Posted by Sailor Steve

On the other hand, there is no way Kongo is going to accelerate to 5 knots in 15 seconds. Should be more like 5 minutes. To 20 knots should take 30 minutes or more. I'll get some numbers from home and put them up tomorrow.

yes i know, the game is hard coded that way. every ship gets a free jump start to 5 kts in way too quickly a speedup. 10-15 seconds is about as slow as i can get but its better than the 2 seconds it takes in stock lol.

my biggest problem is turning and the amount of speed that is lost. what do you think about the turning deceleration speeds?

Originally Posted by WEBSTER

my test doesnt include reversing engines.

i figured stopping by reversing engines would be about the same as acceleration speeds so i figured i would assume they are the same but i will check this at a later time.

[jmardlin]

They wouldn't be because reversing engines even at back emergency only uses about 2/3's ships power. So stopping distances should be slightly longer. But not by much because the screws are much more efficient running backwards because of less turbulence in the water.

[vanjast]

Webster, I found this in the 'attic', and might be useful information.

[Sailor Steve]

Originally Posted by jmardlin

They wouldn't be because reversing engines even at back emergency only uses about 2/3's ships power. So stopping distances should be slightly longer. But not by much because the screws are much more efficient running backwards because of less turbulence in the water.

Drag helps as well. Reversing the engines to stop the ship should make a big difference.

Here are the numbers I promised. The first is a graph made for a naval wargames study back in 1929. Kongo should be in the same area as Repulse.


This is an actual acceleration board from a WW2 aircraft carrier. Sorry I can't remember which one, but at the time I wasn't in a position to record where stuff I was downloading came from.

[gimpy117]

this would really change the game. ships can't just accelerate to avoid torpedoes as well anymore and V&W destroyers (or the Japanese equivalent) can't come screaming in at 35 knots to ram you after traveling with a convoy at 7 knots.

Originally Posted by vanjast

Webster, I found this in the 'attic', and might be useful information.

thanks

Originally Posted by gimpy117

this would really change the game. ships can't just accelerate to avoid torpedoes as well anymore and V&W destroyers (or the Japanese equivalent) can't come screaming in at 35 knots to ram you after traveling with a convoy at 7 knots.

well there is a hard coded issue where all ships get a free jump to 0-5 kts in 10-15 seconds and from 5 kts up you can actually control what they do, so they still can move out of the way on you but a bow shot should clip them in the rudders unless your too far away. but this is still better than stock where they go 0-5 kts in 2 or 3 seconds.

[JREX53]

Originally Posted by WEBSTER

well there is a hard coded issue where all ships get a free jump to 0-5 kts in 10-15 seconds and from 5 kts up you can actually control what they do, so they still can move out of the way on you but a bow shot should clip them in the rudders unless your too far away. but this is still better than stock where they go 0-5 kts in 2 or 3 seconds.

Webster,

That isn't exactly accurate. I have been able to get merchant ships to only make 5 to 6 knots in the 1st minute, and to get them so that they don't reach their top speed for up to 20 minutes by just changing the engine HP and engine RPM.

As a suggestion, I would not use just the drag coefficients to cause the speed changes. You lead yourself open for weird things to happen in game.

Originally Posted by JREX53

Webster,

That isn't exactly accurate. I have been able to get merchant ships to only make 5 to 6 knots in the 1st minute, and to get them so that they don't reach their top speed for up to 20 minutes by just changing the engine HP and engine RPM.

As a suggestion, I would not use just the drag coefficients to cause the speed changes. You lead yourself open for weird things to happen in game.

i havent messed with rpms yet...

[JREX53]

Webster,

That is what I am getting at. You have changed the drag coefficients unnecessarily.
The advice I was given by Sam (swdw), who started the initial physics work for SH4, gave me was to adjust the engine HP until you get into the ballpark, then adjust the engine rpm to get what you want, otherwise if you just change the drag coefficients you are asking for the ship to do weird things ingame.

He also said that because of the game engine was to try to set your timings with about 3 or 4 knots below top speed. The game engine actually slows down the rate of acceleration so that the ship doesn't overshoot its max speed.

Another point of interest is trying to get the ships to use reverse engine speeds you almost have to box the ship in so that it cannot turn. I have tried to get it to use reverse speeds by putting a ship in its path, but it will turn to avoid the ship instead of using reversing speeds.