Why do my Task Force ships sometimes collide?

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IV/JG7_4Shades
Posts: 2201
Joined: Mon 08 Jan 2007 11:10 pm
Location: Perth, Western Australia

Why do my Task Force ships sometimes collide?

Post by IV/JG7_4Shades »

Hi Everyone,

Occasionally I get reports where ships that are Task Force members collide. This had me confused for a long time, because SEOW is very careful to give ships in task forces equally spaced waypoints at all times. Just recently in the SEOW Aces campaign, two such collision instances occurred.

After checking out the SEOW task force waypoints of the offending mission, I could see nothing particularly wrong there. But when I ran the mission, the collision indeed occurred. Some further experimentation showed the following things:

1/ In each of the Aces missions where the collision occurred, the task force was ordered to stop.
2/ In each task force, there was a mix of large and small vessels.
3/ In each case, a small ship and a large ship collided.
4/ In each case, the collision happened near the stopping waypoint.

The evidence was that stopping and vessel mix together caused a problem. So I created a little test coop in FMB to see whether ships of different sizes slowed down to stop at different rates. Here is the test. Two ships steam north, starting level and moving at the same speed. One ship has a final waypoint a km or so north; the other continues steaming at constant speed north. If the stopping ship is heavy, say a battleship, it starts slowing down early so it can stop in time. If it is light, say a PT boat, it can steam almost right up to the stopping point before rapidly decelerating. Here is the test .mis file with a Marat and G5 gunboat.

Code: Select all

[MAIN]
  MAP CoralSea/load.ini
  TIME 12.0
  WEAPONSCONSTANT 1
  CloudType 0
  CloudHeight 1000.0
  army 1
  playerNum 0
[Wing]
  USN_VF_8A00
  USN_VF_8A01
[USN_VF_8A00]
  Planes 2
  Skill 1
  Class air.F4F3
  Fuel 100
  weapons default
[USN_VF_8A00_Way]
  NORMFLY -491677.97 -492483.44 500.00 300.00 &0
  NORMFLY -490697.96 -491190.53 500.00 300.00 &0
[USN_VF_8A01]
  Planes 1
  Skill 1
  Class air.A_20C
  Fuel 100
  weapons default
[USN_VF_8A01_Way]
  NORMFLY -408061.22 -414303.49 500.00 300.00 &0
[Chiefs]
  0_Chief Ships.Marat 1 0 2 1.0
  1_Chief Ships.G5 1 0 2 1.0
[0_Chief_Road]
  -491146.47 -492320.69 120.00 0 2 8.333333969116211
  -491146.25 -490000.47 120.00
[1_Chief_Road]
  -490944.44 -492320.13 120.00 0 7 8.333333969116211
  -490943.53 -491933.50 120.00
  -490942.63 -491546.91 120.00
  -490941.69 -491160.31 120.00
  -490940.78 -490773.69 120.00
  -490939.88 -490387.06 120.00
  -490938.97 -490000.47 120.00 0 38 8.333333969116211
  -490913.59 -489605.00 120.00
  -490888.25 -489209.53 120.00
  -490862.88 -488814.03 120.00
  -490837.50 -488418.56 120.00
  -490812.13 -488023.09 120.00
  -490786.78 -487627.63 120.00
  -490761.41 -487232.13 120.00
  -490736.03 -486836.66 120.00
  -490710.69 -486441.19 120.00
  -490685.31 -486045.72 120.00
  -490659.94 -485650.25 120.00
  -490634.59 -485254.75 120.00
  -490609.22 -484859.28 120.00
  -490583.84 -484463.81 120.00
  -490558.47 -484068.34 120.00
  -490533.13 -483672.88 120.00
  -490507.75 -483277.38 120.00
  -490482.38 -482881.91 120.00
  -490457.03 -482486.44 120.00
  -490431.66 -482090.97 120.00
  -490406.28 -481695.47 120.00
  -490380.94 -481300.00 120.00
  -490355.56 -480904.53 120.00
  -490330.19 -480509.06 120.00
  -490304.81 -480113.59 120.00
  -490279.47 -479718.09 120.00
  -490254.09 -479322.63 120.00
  -490228.72 -478927.16 120.00
  -490203.38 -478531.69 120.00
  -490178.00 -478136.22 120.00
  -490152.63 -477740.72 120.00
  -490127.28 -477345.25 120.00
  -490101.91 -476949.78 120.00
  -490076.53 -476554.31 120.00
  -490051.16 -476158.81 120.00
  -490025.81 -475763.34 120.00
  -490000.44 -475367.88 120.00
[NStationary]
  0_Static vehicles.stationary.Smoke$Smoke2 0 -491209.09 -490004.60 360.00 0.00
  1_Static vehicles.stationary.Smoke$Smoke2 0 -490990.88 -490007.36 360.00 0.00
  2_Static vehicles.stationary.Smoke$Smoke2 0 -491262.16 -490004.60 360.00 0.00
  3_Static vehicles.stationary.Smoke$Smoke2 0 -491072.30 -490005.98 360.00 0.00
  4_Static vehicles.stationary.Smoke$Smoke2 0 -490877.39 -490005.98 360.00 0.00
  5_Static vehicles.stationary.Smoke$Smoke2 0 -490805.29 -490007.36 360.00 0.00
[Buildings]
[StaticCamera]
  -490562 -490616 100
[Bridge]
[House]

The findings are:

(a) Different ship classes decelerate at different rates. It takes big ships longer to slow down than small ships, so the big ships start slowing down earlier than the little ships.
(b) Because of (a), large changes in Task Force speed can cause relative ship positions between waypoints to vary if there is a mix of ship classes. This can be enough to cause a collision before the next waypoint is reached, especially if a small ship is directly behind a large ship.


OK, how can we avoid this problem? Well, knowledge and planning skill helps. Also, using the "Truncate Sea Missions" option helps, because you often don't have to plan stoppages, you can run right over the mission hosting time and the system will handle the stoppage for you out-of-game. Even with this option set, you may still need to stop your task force during the mission sometime. So let's propose a couple of rules:

Rule 1
Try to constitute your task forces with ships of similar size/weight.

Rule 2
Move your task forces gently, with careful accelerations to speed and careful decelerations to a halt. After all, this is what a convoy commander would do in real life.

Cheers,
4Shades
Last edited by IV/JG7_4Shades on Fri 21 May 2010 11:36 pm, edited 1 time in total.
IV/JG7_4Shades
SEOW Developer

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Hitcher
Posts: 117
Joined: Wed 10 Jan 2007 9:30 pm
Location: The Red States

Post by Hitcher »

Excellent info!

Shades,

If I create a template with ships set close enough to be a task force but spaced and positioned so that no ship is directly in front of nor behind another, will I ever have to worry about this issue, regardless of ship size/class?
Hitcher
IV/JG7_4Shades
Posts: 2201
Joined: Mon 08 Jan 2007 11:10 pm
Location: Perth, Western Australia

Post by IV/JG7_4Shades »

Yes you will still have to worry. SEOW maintains the relative positions of all ships in task forces, so if you turn your task force to move in the wrong direction, you can be unlucky enough to achieve a direct alignment of ships.

Here's a simple example. Consider a TF with just two ships. The TF Leader is a carrier with a destroyer as TF subordinate. The destroyer is 2 km directly south-west of the carrier. You move the TF due north and tell it to stop there. At all time during that movement, the destroyer is south west of the carrier, on a parallel track to the carrier. No collisions are possible.

In the next mission, you start the TF moving north again, then after a while you tell it to move exactly north-east. Once the TF swings onto its north-east heading, the destroyer (still located exactly south-west of the carrier) starts following directly in the carrier's path. This is the recipe for disaster, but only if the speed changes are too abrupt.

Cheers,
4Shades
IV/JG7_4Shades
SEOW Developer

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Zoi
Posts: 268
Joined: Fri 14 Jan 2011 3:20 pm

Post by Zoi »

So if truncate is turned on do the ships start and end at the speed they are set at for waypoint 0 and the last waypoint speed in each mission?
IV/JG7_4Shades
Posts: 2201
Joined: Mon 08 Jan 2007 11:10 pm
Location: Perth, Western Australia

Post by IV/JG7_4Shades »

Yes, I believe so, in the main. However, in HSFX5 there is a "ship slowdown" mod that actually reduces ship speed in-game if the ship is damaged. SEOW tries its best to detect slowdown events and adjust ship placements etc, but it does get complicated.

Also, since posting this thread I have altered ship movement orders in mission files to reduce the differential acceleration issue noted above. Usually, these days, ship collisions are overwhelmingly due to command error. With the slowdown feature above, collisions are perhaps more likely because any given damaged ship may not stick to its task force position and may not be where the commander thought it ought to be during a mission.

Cheers,
4S
IV/JG7_4Shades
SEOW Developer

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