Japanese Merchant Convoy Composition

[Mike Solli]

I've been wrestling with how to move the millions of resources from various areas to Honshu each month most effectively. Basically, it comes down to the composition of the cargo TF. (I'm pretty sure the same will go with the TK TFs as well, but I haven't looked at that in nearly the same detail.

Anyhoo, I came up with about four different ways to look at creating a merchant convoy. Before I describe them, here are a few assumptions.

-The convoy will be a continuous convoy between two ports, the originating port and a port in Honshu.
-The maximum size of the convoy will be <the maximum size (tonnage) allowed for the smaller of the two ports.

So, here's what I came up with:

1. The TF will be composed of as many cargo ships as possible that will be filled in 1 day at the originating port.
2. The TF will be composed of ships allowing some multiple of the daily cargo load capacity as possible.
3. The TF will be composed of <50% of the maximum tonnage for the smaller port.
4. The TF will be composed of as close to 100% of the maximum tonnage for the smaller port as possible.

Ok, let's discuss them:

1. This was my original thought. The idea was to have the convoy spend exactly one day in port each way. I figured that if this were the case, the port would be tied up as little as possible. Not bad for the short hops, but for the longer legs the TFs are spending most of their time in transit. Another problem that cropped up was that most of the classes don't fit well into the maximum that a port can load into a ship in a day. There would often be unused cargo space. Definitely not efficient. Besides that, the TFs would have to be manually sent to their destination. Too much time. I want the TFs to be fire and forget. CS missions are the way to go. This was a no go after much brain sweat.

2. The next evolution of my thought on this topic was to have multiple day load time. Yeah, it's better than one day, and you don't have to manually send the TF on it's way, but it still didn't really satisfy me. I wasn't happy with this one so I put it on the back burner and continued to ponder this problem.

3. Then I had an epifany! The best way to make the merchant TF convoys efficient was to build them around the tonnage capability of the port. My first thought was to use convoys that were as close to 50% of the maximum port dockage size as possible. That way, if two convoys happened to overlap in one port, neither one would have to sit around and wait for the other to load/unload and move out. Brilliant! Well, not really. In order to move the amount of resources I have to move, I'd need twice as many convoys. That would mean many more escorts which aren't really available, as well as more fuel burned for those extra escorts. Nope, not good enough.

4. Now I figured that if I maximize the tonnage, based on the lower port level, I wouldn't have to worry about how long it'll take to load. That's not entirely true. I still have to worry about the number of days it'll take to make a round trip, but once I figure that out (pretty simple really), I can calculate how many resources that TF will haul in a month. I have worked out which ports I'm using to load the stuff and each has been given a base in Honshu to unload it. If that route can move enougth to keep up with that region's production, we're good. That's unlikely in most cases. I can add a second convoy that moves in the opposite direction so they'll only meet in mid-ocean. No harm done and no port back-up. Most regions have more than one base to load resources anyway. In most cases, the loading and unloading ports are the same size. That's not always the case though. There are a few that I am going to increase in size to allow bigger TFs to run out of them.

I still have a lot of the grunt work to do in order to set the TFs up, but I'm pretty happy with my plan. What do you guys think?

[erstad]

What I'm doing is closest to #4. Convoys sized by the smaller port. But in many cases I have more than one or two; I've got up to 4 plying the same route.

[pompack]

Well Mike, I kinda approached it from a different direction. This example is for resources; oil is more complex because there are fewer size choices for tankers.

Assume little ships are less efficient (ton-miles move per dollop of fuel); note that every ship will be sailing every day (unless loading/unloading) but the short haul routes will spend proportionally more time loading/unloading thus that is where you want the small ships.
Assume that I will deliver to a port that is the same size or larger than the source port
Assume that escorts will be the limiting factor so strive to maximize the convoy size
Assume that all of the two smallest AKs are converted to PBs

So I find the closest port that is a source of goodies.
I take one escort (1941, I expect to have to add an additional escort every six months as the subs get better) and as many of the smallest AKs required to be just below the size of the source port.
I determine the transit time; divide capacity by twice transit time plus two days (not always true but this assumes one day load/unload) to give mean daily transfer rate (MDTR); divide daily resource production (or overland movement if port not resource center) by MDTR to determine ROUGHLY how many convoys are required to service the source.
Create the required number of convoys and start them moving. Note that they will bunch up at first but that doesn't matter; in the steady state they will NOT interfere unless you have created too many convoys.

Now repeat for each successively more distant source. Note that as you go further out, the ships in the individual convoys get larger simply because you run out of small ships.

Now I have found that the source ports are not fully utilized; a level 3 port is capable of handling 10k- 20k (big ship versus little ship) and that is more than can be made available in every case I have found (so far). The bottleneck can come at the receiving end with many convoys coming into a limited number of ports at irregular intervals. HOWEVER I have found that there are not really a limited number of ports. The trick is to insure that you direct (for as long as possible) single convoy STREAMS to a single port. When you have a case where the desination port is big enough to simultaneously take a convoy for each of two (or more) streams, then you can direct those multiple streams to a single port.

Now you will still run out of ports that way, so the next step is to monitor the loading of each destination port: a destination port can be considered as a one-convoy-port or a two-convoy-port, etc based upon the size of the convoys and the port. Each day simply note how many additional convoys of the largest size scheduled for that port could be accomidated there and note the most underutilized port on Honshu (this is actually more rigorous than necessary, I just eyeball it myself). When it is necessary to add the next convoy stream, route it to that port. As usual, there will be short-term conflicts but they will work themselves out as the convoys space out to to initial congestion (usually, there will always be recurring conflicts due to the beat frequecies generated by the varying convoy voyage times from different streams using the same destination port.)

The selection of a destination port is not as significant as it seems at first glance. When you use multiple destination ports, some convoys will have to steam further than others but it really doesn't matter that much as long as you avoid crossing routes (e.g. a southbound convoy from Sakahlin heading for Hiroshima meeting a northbond convoy from Luzon heading for Hirosaki would be a Bad Thing). By spreading the load among many destination ports you do tend to increase the sailing distance but you drastically reduce the congestion at the few big ports. Also note that you should be cautious about using a destination port that is adjacent to port on another island; that can reduce the amount of inter-island transfer by "osmosis" and require you to use precious shipping for inter-island transfers.

Now reading this, it sounds much more complicated than it really is. At a basic level it is use convoys that fit the source port and send them to as many destination ports as possible. They will conflict at first but then space themselves out automatically

[Historiker]

How much does it take to expand the ports to a size +3? If that allows you to ship more ressources in, it'll be defenitly worth it.
Cncerning how much supplies you loose if you can't ship in enough ressources, expanding ports to their absolute maximum can't be too expensive.

Calculation with the TF size is second to me. More important is the production at the pick up port. One should rather calculate how much to pick up is there than how much can be picked up by ships. If you know you TF will come every 15 days, the TF must have the size to pick up the 15days production, no matter its size. The size only gets important if the port is too small and forces you to send additional TFs. To keep it simple one might also accept the penelty haveing an oversized TF and calculate with the consequently higher loading times.

[vlcz]

Very interesting thread.

Do you know if waypoints asigned to a TF we put in CS are followed in each travel? will be very desirable avoid massive ambushes stopping all trafic

[Mike Solli]

ORIGINAL: Historiker

How much does it take to expand the ports to a size +3? If that allows you to ship more ressources in, it'll be defenitly worth it.
Cncerning how much supplies you loose if you can't ship in enough ressources, expanding ports to their absolute maximum can't be too expensive.

I have no clue other than to state the obvious. It costs much more supply to increase a 2(2) port to a 3(2) port than it does to increase a 2(3) port to a 3(3) port. My goal is to avoid the former and do only the latter when absolutely necessary.

[Historiker]

But how much will it cost? My experience is, building it three times bigger doesn't cost more than some thousand supply, maybe 10 or 15.000. But that's it.
If this means you can dock more, load and unload faster (you can in bigger ports, right?) it should be worth it. Not to mention that ships also repair faster, then.

This also means more points (for the ones that concern about points) and: less spoilage! Especially this should be worth to mention!

[Mike Solli]

pompack, very interesting.&nbsp;
&nbsp;
I like the idea of several single convoy streams going to one port.&nbsp; That infers that the target port is one of the large ones, but I guess it all depends on the size of the convoys.&nbsp;
&nbsp;
Three of the Home Islands produce a small excess of oil (~17k per month).&nbsp;&nbsp;It'll take&nbsp;some calculating, but I'll bet a single convoy of a couple of small TKs or one Manzu can take care of all of them.
&nbsp;
I'm not sure you can assume a one day load/unload time for the oil convoys.&nbsp; Are you setting them up to be able to do that?
&nbsp;
One other thing I forgot to mention.&nbsp; I've given up on the efficiency thing.&nbsp; We're going to need every hull we have, so I don't think it really matters.

[Mike Solli]

ORIGINAL: Historiker

But how much will it cost? My experience is, building it three times bigger doesn't cost more than some thousand supply, maybe 10 or 15.000. But that's it.
If this means you can dock more, load and unload faster (you can in bigger ports, right?) it should be worth it. Not to mention that ships also repair faster, then.

This also means more points (for the ones that concern about points) and: less spoilage! Especially this should be worth to mention!

You're right, of course. Since we really don't know how much supply it costs, the way I handle supply is to be very conservative early on. I allocate a set amount of supply to operations, with a reserve that I don't touch unless absolutely necessary. I also track about 20 or so stats daily. I want to catch trends before they become critical. As long as my total supply doesn't drop suddenly, I know I'm doing ok and can change things slowly. I have a list of all things going on that can consume extra supply (building ports, airfields & forts, etc.). Everything doesn't have to begin on 7 Dec. I slowly add items every day or so after checking to make sure the supply can handle it.

[pompack]

ORIGINAL: Mike Solli

I'm not sure you can assume a one day load/unload time for the oil convoys.  Are you setting them up to be able to do that?

One other thing I forgot to mention.  I've given up on the efficiency thing.  We're going to need every hull we have, so I don't think it really matters.

Unload time: true but the important thing in my method is to avoid too many convoys to the same source; by assuming one day turn around you will add a little pad to the calculation (and it is easier to do in your head). Since the actual calculations always give answers like 2.4 convoys (and you always round down of course) if you get a solution that is close (e.g. 1.9 convoys) I calculate it more closely using more accurate load times for that specific convoy stream.

Hull numbers: yep, but the real problem is going to be escorts downstream. In early 42 one escort is usually enough; I rarely even get shots at subs but the subs are not taking shots at the merchies either. I think I have lost three merchies (and two Japanese subs!!) to Allies subs but I have lost four escorts. The escorts have yet to sink a sub as well. I had planned to add one escort the the convoys every six months but the way the activity is picking up as time goes on that is probably not going to be enough since it will be May43 before I plan on four escorts per convoy and that looks to be too late. Also note that tankers are so precious that I use 4-6 escorts per tanker convoy from the very beginning (but I run out of escorts very quickly that way)

[Mike Solli]

I count 300 escorts and potential escorts at start.&nbsp; That's broken down as&nbsp;follows:
&nbsp;
Shimushu: 4
Hashidate:&nbsp;3
Momi (E): 5
Momi (PC): 5
Otori: 9
Tomozuru: 4
Kiso PB: 31
Ansyu PB: 52
To'su PB: 34
Ch: 23
CHa: 24
&nbsp;
Potential conversions:
Kiso: 69
To'su: 37
&nbsp;
Granted, some of them don't even carry DC racks, but they can work in conjunction with those that do.
&nbsp;
We also have 9 AMCs with a few more building.&nbsp; I'm tempted to use them as decoys along routes with known sub infestations.&nbsp; Imagine an Allied sub surfacing to hit one of them only to see some 8" guns popping them. [:D]
&nbsp;
I'm not nearly done with planning my convoys yet.&nbsp; I can see those 300 being tasked out very quickly.

[Q-Ball]

Oh boy.....escorts. This could be a separate topic. What are you guys doing in this space?

It appears that everything needs to be escorted now. In WITP, I would routinely not escort low-priority convoys, but it looks like that's a bad idea now. Given that, I think there is a greater need for escorts than in WITP.

Surface attacks by submarines must be prevented. I think it's true, but any old scow with a gun is sufficient to keep a sub submerged, right? I am thinking of the Tos'u-class PB's, which about all you can say about them is that they are a boat with a gun on it.

Does an escort have to have DC racks to keep a sub down? Most escorts don't cause alot of damage anyway to Subs (or they didn't in WITP), so if the objective is to just make a sub use torps, wouldn't a warship with guns be sufficient? (I am thinking of the Sokuten-class minelayers; without mines, they end up sitting around in port alot). Or an AMC? Any idea?

I plan to use Tos'us primarily around Japan; the resource convoys in my mind will consist of smaller, shorter-legged, and slower classes (Daigen Cargos, AKLs, etc), for which the Tos'us slow speed and short-legs don't matter. 1 escort per TF should be OK initially.

I plan to use the 10-kt. Cha-classs SCs around Japan proper, to prosecute sub sightings. They are slow and short, but they do have alot of DC racks, and I plan to deploy 2 or 3 4-ship ASW TF's around the Home Islands.

I am converting some Ansyu-C PB's for longer-range escort, and some Kiso-Bs to escort cargo shipping. There is a shortage of faster escorts, may need to detail older DDs to escort valuable tanker convoys.

IN WITP, the number of escorts didn't make a huge difference it seemed to me; I ran a ton of convoys with one or two escorts only. Maybe that's different in AE, hope it is, because the more escorts there are, it should be harder for sub captains to get hits.

[Historiker]

I hope for airbased ASW and plan to use as much bombers as needed for that role, even if that means 50% of my bombers do that job.

I guess - though not tested - that there'll be an immediate need for escorts in the beginning as long as the Asiatic fleet has bases and isn't sunk, yet. Also, the ASW units have to get experience. I hope this stabilizes in 1942 to get serious in 1943 again. I also hope there'll be enough escorts, then.

Does anyone of you have a clue how the ressources flow in the Jap islands? It would be really sad if you plan it into in details where how many ships have to come how often... just to find out that the ressources accumulate at other bases...

[Mike Solli]

ORIGINAL: Historiker

I hope for airbased ASW and plan to use as much bombers as needed for that role, even if that means 50% of my bombers do that job.

I guess - though not tested - that there'll be an immediate need for escorts in the beginning as long as the Asiatic fleet has bases and isn't sunk, yet. Also, the ASW units have to get experience. I hope this stabilizes in 1942 to get serious in 1943 again. I also hope there'll be enough escorts, then.

Does anyone of you have a clue how the ressources flow in the Jap islands? It would be really sad if you plan it into in details where how many ships have to come how often... just to find out that the ressources accumulate at other bases...

If you're going to use the IJAAF for ASW, you'll need to do some serious ASW training first.

I don't know how resources flow in the Home Islands. I assume (possibly a big assumption) that it's the same as in WitP. In WitP, I never had problems with stuff moving around the islands. The AI did a good job of making sure stuff went to where it was needed every 3 days. I do know that Honshu will need 110k resources a day shipped in to keep the HI and LI functional.

[crsutton]

My experience is really only on the Allied side but I am finding that even one lowly escort for a convoy makes a significant difference.

[Shark7]

I'm still using my vanilla scheme of 1:2 and 1:4. That is 1 escort for every 2 tankers, and 1 escort for every 4 AKs. Just not enough escorts available to properly defend the convoys.

[vaned74]

I did a quick count of the escorts I have available in my current PBEM (late Feb, 42)

MGB x 6
SC (Cha) x 28
SC (Ch) x 28

These will be used mostly at key points in 2-4 ship groups as local patrols, protecting harbors etc from pesky subs entering the hex.

Longer range escorts
Kiso class PBs (spd 11, range 4,000) - 68 ships
Ansyu PBs (spd 14, range 6,000) - 113 ships
To'su PBs (spd 12, range 1,700) - 15 ships

The Ansyu's will be used for longer route convoys if 12-14 knot speed. The Kiso for more local convoys and the slower ships.

The To'su will be assigned exclusively for local convoys (short hoppers of AKLs, slow, small AKs).

Other small craft, escort type assets include:

DMS x 18
CMc x 11
CM x 24
ACM (4,000 endurance) = 1
ACM (2,100 enduramce) = 74
AMc (2,100 endurance) = 28
AMc (4,000 endurance) = 37

PC x 5
E Hashidate x 3
E Shumushu x 4
E Momi x 6

I also plan to allocated all the old destroyers to tanker escort duties and the occasional dedicated ASW task force for key routes/locations.

[Historiker]

There is not a single escort that can run the distance from Palembang to Osaka and back without refueling.
So either one has to break the convoi to refuel just the Escorts in the Home Islands (to save fuel there and refuel the cargo ships in Palembang) or one has to accept that the transports immediatly take some of the fuel they've brought to sail back to the SRA.


Edit:
Wrong: The distance is 6240 so
Akizuki DD
Etorofu E
Shimushu E
Type C E
are all ships available for that task.

[Mynok]

Just let them refuel from the transports. Non-issue IMO.

[Historiker]

hmm?

PBs, SCs and Es refuel from ordinary AKs and TKs???