Another dumb question about mines

[HansBolter]

How can a minefield in a river be completely bypassed by a TF that transits through that hex down the river?

Does the minefield I set in the river not span across the river? Is it simply concentrated in the mouth of the harbor of the port along the river where I set it?

In my current game the Chines have retaken Nanking and Shanghai. The Japanese have a large force surrounded at Wuchang. They have ben running supply down the river so I established a minefield at Nanking.

Day after day one IJN TF after another blows right through the field without ever encountering a mine.

This seems odd. While the minefield is still small (153 mines last turn) it IS in a river hex which represents far, far less area to concentrate it in than a coastal hex.

How exactly are they bypassing the minefield?

These are really big ships, not like a canoe that can simply be portaged around the block in the river.

[dr.hal]

Interesting point Hans. I think the answer is simple (although I'm really guessing here) due to the game's complexity. The simple fact is that a "coastal hex" is a coastal hex no matter how much of the hex is land or water, it will have the same impact in terms of chance to hit with mines as any other coastal hex no matter what the ratio of land to water is. To "calibrate" each hex into how much is land and sea (including river hexes) would be exceedingly complex and probably not seen as worth the "squeeze" when the game was designed. The same is true for searching; if I have an air unit of Petes for example, set to ASW search from a shore hex and the shore line bisects the search area but yet I set no arcs for the plane's search zones, I expect that half the effort will be over land (where subs are normally not known to go!). This is simply due to the fact that search arcs take care of the problem, but require player intervention, and if no player intervention, the "dumb" computer gaming system (no slight intended here, as the game is already VERY complex) simply searches ALL hexes, no matter the type. So if a hex has a TINY bit of water in it and you plant 150 mines, it will have the same chances of a hit as a hex that is 90% water. That's how I read the tea leaves anyway. Others certainly know more about the game than I. Hal

[HansBolter]

That's pretty much what I was thinking big red eye.

I just wanted to point out how silly the outcome seems.

[Yaab]

Bypassing minefield on rivers contradicts the manual

p.39

4.2.1.4 NAVIGABLE RIVERS
Navigable rivers are rivers that ships may “sail” along. In map terms, they are river hexsides
that naval TFs can move across. Navigable rivers have the following effects and limitations:
»» Only ships with tonnages of 15,000 tons or less
may cross navigable river hexsides.
»» The hexsides have effects on naval units that are similar to narrow straits – TFs
crossing them are more vulnerable to mines and any CD units that are present.
»» TFs will not react along a river unless the range to the enemy is one hex.
For ground units, navigable rivers act in the same way as any other river.

[dr.hal]

ORIGINAL: Yaab

Bypassing minefield on rivers contradicts the manual

p.39

4.2.1.4 NAVIGABLE RIVERS

»» The hexsides have effects on naval units that are similar to narrow straits – TFs
crossing them are more vulnerable to mines and any CD units that are present.

Thanks Yaab, I forgot about that rule, so indeed for rivers and choke points there is a mitigating circumstance that enhances the impact (pun intended) of mines. That's more "realistic".

[Alfred]

It is more complicated.  In fact it might even be a candidate for the Tech sub forum to get michaelm to look at the code.
 
 
First the easy bit, just to provide some context.
 
1.  You could be the victim of bad die rolls.  The number of mines present is not as important as the number of minefields present.  If all 153 mines are in one discovered minefield, then it is easier to get a bad die roll.  No mention of how many transits have occurred without "incidents", nor how many enemy vessels transited together.
 
2.  Any hex which has both land and ocean terrain is considered to be coastal.  The percentage of land v ocean is unimportant to the code.
 
3.  As far as the code is concerned, there is no difference between shallow ocean and deep ocean except in two matters:
 
(a) subs are easier to detect in shallow ocean
(b) mines disperse faster in deep ocean
 
4.  Back in 2008 it was directly asked whether it was possible to mine rivers.  The answer from Andrew Brown was yes because they were coastal hexes.
 
5.  In AE movement is across hexsides, not along hexsides.
 
6.  Ships can only cross blue or white hexsides.
 
 
Now for the difficult bit.
 
7.  What complicates naval movement is a navigable river.  Unlike other terrain, the hexsides of a hex with a navigable river provide no visible cue that naval movement is allowed.  The hexsides are purple which means a river hexside allowing only ground  unit movement.
 
8.  The Yangtze is by far the longest navigable river in AE.  It is possible to sail ships of up to 15k tons all the way up to Wuchang.  But, if you look closely, the navigable river graphic is only present from Nanking to Wuchang.  Those hexsides are either green or purple.  However, between Nanking and Shanghai there is either a blue or white hexside which clearly allows for any ship to transit.
 
9.  If you look at the other navigable rivers, you will find the navigable river graphic is present all the way from the river mouth to the river port.
 
 
Because the naval movement on the Yangtze is represented both by the navigable river and the blue/white hexside code, it is therefore possible that a small bug exists to not recognise the existence of a minefield at the junction of the two.
 
Alfred

[Rising-Sun]

Mines in river is more likely to get hit, unless you are paddling a canoe.

[Lowpe]

Perhaps the Japanese have cottoned onto the polarity of the mines and reversed the polarity of their ships.

Happened in real life....oh, that the Allies figured it out against German mines. Japan got trashed by mines, so much so that it was top secret until the 1980s I believe.

PS: I like Alfred's explanation far better though.[;)]

[HansBolter]

Thanks for the analysis Alfred.

I had no idea I might have stumbled onto something that may deserve a look into.

[dr.hal]

ORIGINAL: Alfred
  The number of mines present is not as important as the number of minefields present. 

Thanks Alfred, but I've got a question. In the above you indicate that a hex can have more than one "minefield". I am assuming that you mean more than one naval minefield per hex, as I don't see how to lay a land minefield. I would like you to expand upon that. As far as I can see on the game board, there is only a "minefield," in a single hex, defensive or offensive. How do you get more than one there? Do you need to plant another type of mine? When I drop a second set of mines in an existing minefield, it seems to simply join the existing minefield, NOT create a new one. In addition, if one drops a second TYPE of mine, does this create a second field? If not, then how is the type of mine selected that is hit? Are there two separate die rolls for each type of mine (much like different caliber naval rifles firing from the same ship or differing machine-guns from a single aircraft, each having a different hit probability and impact)? If this were the case, then it would be advantageous to lay a second "field" of a different type, thus getting two "attacks" albeit with less mines in each. What say you?

[HansBolter]

ORIGINAL: dr.hal

ORIGINAL: Alfred
  The number of mines present is not as important as the number of minefields present. 

Thanks Alfred, but I've got a question. In the above you indicate that a hex can have more than one "minefield". I am assuming that you mean more than one naval minefield per hex, as I don't see how to lay a land minefield. I would like you to expand upon that. As far as I can see on the game board, there is only a "minefield," in a single hex, defensive or offensive. How do you get more than one there? Do you need to plant another type of mine? When I drop a second set of mines in an existing minefield, it seems to simply join the existing minefield, NOT create a new one. In addition, if one drops a second TYPE of mine, does this create a second field? If not, then how is the type of mine selected that is hit? Are there two separate die rolls for each type of mine (much like different caliber naval rifles firing from the same ship or differing machine-guns from a single aircraft, each having a different hit probability and impact)? If this were the case, then it would be advantageous to lay a second "field" of a different type, thus getting two "attacks" albeit with less mines in each. What say you?

Very good questions Hal. The minefield(s) we are discussing were laid in two runs of 100 mines each by a US fleet boat TF of 5 subs carrying 20 mines each.

The first group of 100 had deteriorated before a second run laid another 100.

So does that mean I have laid two separate minefields?

[Lowpe]

Correct. You would have been better off having those subs lay mines in individual, single ship, task forces. Your chances for hits would have grown dramatically, plus, the chance some stay hidden longer further increasing your chances for a hit.

[dr.hal]

If this is correct, that's a game changer in terms of strategy.

[HansBolter]

ORIGINAL: Lowpe

Correct. You would have been better off having those subs lay mines in individual, single ship, task forces. Your chances for hits would have grown dramatically, plus, the chance some stay hidden longer further increasing your chances for a hit.

Which begs the $64 question.....

does that mean each individual minefield is subject to a decay rate or only the total of all the minefields in the hex?

If only the total what determines which minefield incurs the decay loss?

If it's each individual minefield incurring the decay that would be a factor that detracts from the increased effectiveness of multiple individual minefields.

[dr.hal]

Hans is that really true? Let's say you have possible deterioration at 1% per turn. If you have 400 mines, that's four mines. If you have four minefields of 100 each, that's one mine per field, but with a total max of four. Now if you get a bad roll on the big field, its four down, but that won't happen as much as you get four chances for a bad roll on four different minefields. So in the long run I think the decay would be about the same. Just a thought, statistically thinking!

[Lowpe]

From our resident expert:

5 minefields of 40 mines (=200 mines in total) is better than a single minefield of 200 Mines. Of course 5 minefields of 200 mine (=1000 mines in total) would be even better but there are logistical reasons why that would be a rare situation.

Alfred

Link:
tm.asp?m=3543958

[HansBolter]

ORIGINAL: dr.hal

Hans is that really true? Let's say you have possible deterioration at 1% per turn. If you have 400 mines, that's four mines. If you have four minefields of 100 each, that's one mine per field, but with a total max of four. Now if you get a bad roll on the big field, its four down, but that won't happen as much as you get four chances for a bad roll on four different minefields. So in the long run I think the decay would be about the same. Just a thought, statistically thinking!

Is decay subject to a die roll or is it an automatic rate of 1% per hex?/minefield? in a coastal hex without a tender?

If automatic more fields equals more lost mines per turn for that increased chance for a hit.

One of the really sweet beauties of this game is never having all the numbers to crunch to determine outcomes.

It takes a LOT of experimentation.

[HansBolter]

ORIGINAL: HansBolter

ORIGINAL: dr.hal

Hans is that really true? Let's say you have possible deterioration at 1% per turn. If you have 400 mines, that's four mines. If you have four minefields of 100 each, that's one mine per field, but with a total max of four. Now if you get a bad roll on the big field, its four down, but that won't happen as much as you get four chances for a bad roll on four different minefields. So in the long run I think the decay would be about the same. Just a thought, statistically thinking!

Is decay subject to a die roll or is it an automatic rate of 1% per hex?/minefield? in a coastal hex without a tender?

If NOT (correction)automatic more fields equals more possible lost mines per turn for that increased chance for a hit.

One of the really sweet beauties of this game is never having all the numbers to crunch to determine outcomes.

It takes a LOT of experimentation.

[Yaab]

Goodbye, your developers have deserted you.

[crsutton]

As an anecdote to the question. My opponent was besieging Diamond Harbor and bombarding it on a daily basis. Over the course of two months I laid substantial and multiple minefields in the hex with subs but found them to be all but useless vs either his bombarding ships or fast transports that were frequently sent into the hex. However, on one occasion he sent a sub upriver to Calcutta and accidentally set a large CA/DD TF to "follow" the sub TF up the river. In passing both up and down Diamond Harbor the CA/DD Tf took catastrophic mine damage-sinking 8 DDs and wrecking a number of CAs. So bad that I gave him a do over. We never really understood the mechanics behind it except that it apparently had something to do with the follow order.