ship stopping distances

[Webster]

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

=======================================

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


=======================================


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

=======================================

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!:woot:

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

[Webster]

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!:woot:

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.

[Webster]

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?

[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 (http://www.vanjast.com/General/ShipPropulsion.pdf) in the 'attic', and might be useful information. :DL

[Sailor Steve]

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.
http://i14.photobucket.com/albums/a325/SailorSteve/accelerationgraph-1.jpg

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.
http://i14.photobucket.com/albums/a325/SailorSteve/Engine9-2.jpg

[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.

[Webster]

Webster, I found this (http://www.vanjast.com/General/ShipPropulsion.pdf) in the 'attic', and might be useful information. :DL

thanks :yeah:

[Webster]

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]

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.

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.

[Webster]

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.

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... :hmmm:

[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.

[vanjast]

Webster,
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. I've noticed shooting a torpedo at the ship causes it to 'put on the brakes'. If you fire all torps at 5 sec intervals in front of the ship it might work.
:)

[JREX53]

Thanks vanjast!!

I will give it a try.

[Webster]

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.
.

the drag coeficients were used from PT's advice and i threw those values i used away and settled on new values.

i worry lowering rpm too much will cause ships that slow for evasive zig zag manuvers to get stuck doing 5 kts trying to regain speed. do you have a suggested number to start at?

[JREX53]

Webster,

I haven't gotten that totally figured out yet. I have been using the same drag coefficients for all ships so far. I have been using the same values for the L/R drag and another value for the U/D drag (both surfaced and submerged).

I too also looked at PT's values and decided not to use them. I am also using a different value for the center of gravity then what he used.

I also noticed that you are using values in both surfaced & submerged drafts (draughts). Is there a reason for this? Not trying to be critical, just curious.:06:

Keep up the good work on this, like Rockin' Robin said a while ago, the more people working on ships physics the better.

[Webster]

Webster,

I haven't gotten that totally figured out yet. I have been using the same drag coefficients for all ships so far. I have been using the same values for the L/R drag and another value for the U/D drag (both surfaced and submerged).

i think the submerged set of values is only used for subs but the reason they are there is thats stock so i just left it. i noticed no difference if they were left as is or set to zero. but i did not spend a lot of time with them so i mighta missed something.


I too also looked at PT's values and decided not to use them. I am also using a different value for the center of gravity then what he used.

im not definate on using that number but i like the heavyness it gives ships like they realy have weight to them so if i change it and i probably will it wont be by much, just enough for proper pitch and roll effects.

i dont know how the devs came up with those numbers but i swear thery just put the railing height or something like but that its definately not the center of gravity for those ships so i dont understand what they were using.


I also noticed that you are using values in both surfaced & submerged drafts (draughts). Is there a reason for this? Not trying to be critical, just curious.:06:

i only changed surface drag and left submerged drag and submerged draft at stock settings. some files have everything filled some dont but its all stock except the following:

ship_class=
(obj_hydro)
gc_height=
(surfaced/drag)
LR=
UD=
(propulsion)
eng_power=
(rudder)
drag=


some of those stock sim files have no mass number but have one number for surfaced displacement and a different number for submerged displacement so ???

Keep up the good work on this, like Rockin' Robin said a while ago, the more people working on ships physics the better.

im afraid we will all end up with 6 versions all simular but different lol. :arrgh!:

you need to get us a keg of beer and some sandwiches and we all meet at your house with our computers and stay there till its finished. :yeah:

[keltos01]

bump