Just been trying to simulate a recreation of a mission from Jun 43, as part of a campaign I'm making. The target was a merchant ship towing 'at least 6 barges' escorted by a Torpedo Boat (sort of small DD, not an MTB-type craft).

I put a Dry Cargo ship in and then added MFPs in its wake with the same, 9 kph, speed. The cargo ship was made a Hidden Target. After about a minute the 'Hidden Target Complete' msg came up. I guessed what was happening and put in some cameras to check it. Sure enough, the MFPs were catching and ramming the cargo ship.

Right, slow the MFPs by 1 kph - they still catch up and it looks like the closure increases as the mission goes on. Rather than keep running the mission with a 1 kph change to the speed of the ship or MFPs each time, I decide to run a race to find out just what speed a cargo ship has to do to match an MFP at 8 kph.

I put an MFP at 8 kph and lined up cargo ships with it - one at 11 kph, one at 12 kph etc to the fifth one at 15 kph. They started with bows aligned and had several hundred metres to cover before the start line of marker flares (in case they take a while to settle at desired speed); a km beyond that was the finish line.

Start the mission and, as expected, the 'faster' ships pull away from the slower ones. Start a stopwatch when the 15 kph ship crosses the start and note times of start/finish for each vessel:

15 kph - 0:00
14 kph - 0:20
13 kph - 0:44
12 kph - 1:07
11 kph - 1:20
MFP (8) - 1:27

That was the only time things went as you might expect. Finish times (time to complete 1 km):

15 kph - 6:15 (375 s)
14 kph - 7:05 (405 s)
13 kph - 8:36 (472 s)
12 kph - 9:05 (478 s)
11 kph - 8:15 (415 s)
MFP (8) - 5:50 (263 s)

Average speeds over the 1 km course are:

15 - 2.67 m/s; 9.6 kph
14 - 2.47 m/s; 8.9 kph
13 - 2.12 m/s; 7.6 kph
12 - 2.09 m/s; 7.5 kph
11 - 2.41 m/s; 8.7 kph
MFP - 3.80 m/s; 13.7 kph

So the only cargo ship to match the supposed default speed of such vessels - 9 kph - is the one programmed to steam at 15 kph; the '8 kph' MFP is faster than all the 'faster' ships; and the '11 kph' cargo ship is quicker than both the '12' and '13 kph' cargo ships.

At this point I realized that my life isn't long enough to work out just how you might match MFPs and Dry Cargo Ships for speed - especially as increasing speed can make it slower The mission just has a merchant ship in it now.

I always thought this function worked and have used it for keeping fleets and convoys together in the past. But maybe the ships were never close enough or the missions long enough for the random speeds to make noticeable gaps appear?

Hmmm, for the next mission I did a speed test right at the start and found the Liquid Cargo Carrier and its escort both completed the 1-km course in 3 min dead when planned at 20 kph... which only makes the previous MFP/Dry Cargo episode more inexplicable.

The issue of ships covering different distances at the same speed has been known for quite a while.

Here is how I solve it. Set up your ships in the formation you want. Run ONE ship of each type out the same distance using the grid as a reference - for example 50km. Ths is NOT the distance you plan on using for the mission. Only use two waypoints to cover the 50km.

Adjust the speed of each ship at both waypoints so that they arrive at the 50km point at the same time. Make sure you move the second waypoint a little each time you adjust the speed as the time does not always reset if you don't.

When you have the different ships arriving at the end waypoint at the same time you now know what speeds to use for your real waypoints.



Calibrate

Thanks, I'll give that a try. I wondered if it might be a known issue, although I'd not come across this one before and I guess the second test showed it doesn't always happen.

quote:

Originally posted by Kernow:
Thanks, I'll give that a try. I wondered if it might be a known issue, although I'd not come across this one before and I guess the second test showed it doesn't always happen.

The problem is that your kilometers per hour is not always represented with the same number in the .mis file.
Different ships for some reason use different speeds in the .mis file to represent the same speed shown in the FMB.
The way I tested this was to put several ships in the FMB with the same speeds and then look at them in the .mis file.
I saw different speeds for some of the ships.

Here is a sample of the way a ship is handled in the .mis file.
The speed for the ship is in yellow.

[Chiefs]
0_Chief Ships.Tanker 2 0 2 1.0
[0_Chief_Road]
84802.48 19496.38 120.00 0 2 3.729722261428833
85044.48 11328.61 120.00

I'll bet if you still have your test mission you will see the same thing.
You set all of the speeds the same in the FMB but they are not the same when you look at them in the .mis file.
You can change the speed to match on all the ships and it should get them to sync with one another.
The only problem you can run into is if the speed you try to set is higher than the maximum allowed for that ship.
It will set itself to the maximum when you try to run the mission.

Here is a chart at M4T that explains the other parts of the lines I didn't highlight.
Description of .mis file properties


Wheelsup

Actually, Wheelsup, that was the first thing I looked at. All the speeds were identical at 2.5xxxxxx etc to a dozen or so decimal places. I changed them to 2.5 to see if a manual entry to the .mis file would make them behave the same, but it didn't work. After that had failed I started playing with the speeds in FMB.

You gotta love the idiosyncracies of FMB & AI eh

oh, thx for link, btw.

Kernow - I've never had this happen.

Did you do a double check on the speed at both waypoints during every test? When I've had problems with ships not behaving as expected it's because I've forgotten to put the speed at all waypoints.

I know this sounds like stating the bleedin' obvious, but I'm really puzzled by this as I've done plenty of ship missions with no problems.....

Yep Phil. And the more I think of it the more I'm certain I've never had it before either.

I went back to that mission and put the barges back in, doing the calibration ZC suggested. Still the MFPs caught the cargo ship. This time the cargo ship had more than 2 WPs - at the time the strike turns up it starts to manoeuvre into one of the attacking groups. At that point I placed the last WP (2nd) for the MFPs, to simulate them stopping once the cargo ship is torpedoed or, if it escapes, to simulate the tow lines being dropped to give the ship more ability to manoeuvre. I suspect the ship was now doing the asked for speed.

I then added another, mid-point, WP for the MFPs and that seemed to solve the problem, until, half-way through, they accelerated into the back of the ship. That seems to explain it: the MFPs will sail at some speed of their own to their last WP and it seems the cargo ship also picks a speed of its own to its last WP, only a slower one.

I've now dragged the MFP mid-point WP to very near the end of their route and it all works as planned, because their last WP is only a few yards beyond WP2. I haven't double checked the speed by measuring it, but as all vessels appear to be doing the same speed, I assume it is the demanded speed.

The tanker and escort both ran exactly as planned with 2 WPs, so this doesn't happen with every ship. I don't even know if this 'bug' would repeat in a different mission or map.

Kernow, going back to the original problem; all you want is for those ships to not ram each other and stay grouped all the same.

Simplest way is to make sure all your ships have their own "lane" so catching up results in overtaking, not ramming.

Also like Phil_K says, the first waypoint needs to have matching speeds for all. That way it will work out just fine ususlly. Agreed, the truncating is mushy and diifficult to control. Patience is the answer; pull back the faster ships' starting waypoint until you are satisfied their position is right when your plane reaches it (or whatever you are trying to do) .

Cheers,

Problem is I wanted them to look like they were being towed by the merchant ship, so they couldn't really go catching or overtaking and they should also follow directly in the wake of the merchant ship. Anyway, putting in more than 2 WPs seems to have solved the problem and doesn't require numerous trial & error runs of the mission.

Thanks for all the suggestions.