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