Whenever I see double stacked intermodal containers of different sizes, the longer container is stacked on top. Intuitively, it seems that greatest benefit would be to have a low center of gravity and a stable base.
What is the strategy for stacking containers? I have also seen this stacking configuration in shipping yards. Since I have never seen a counterexample, it seems to suggest that there exists a good reason for stacking it this way. I just can't fathom what that reason is.
Sorry if this issue has been tackled before. I searched for a while, but the search terms are pretty generic (intermodal, long, short, double stacked, etc) so my searches were returning more noise than signal.
Thanks,
Claire
ClaireWhenever I see double stacked intermodal containers of different sizes, the longer container is stacked on top
I'm trying to think about that and isn't it a fact the "well" cars support shorter containers in the well and the 53's must go on top as they are too long to fit down in the well, hence can't go on the bottom.
Quentin
That's a good ?. Maby if you put the big container on bottom the drag would slow down the train.
The road to to success is always under construction. _____________________________________________________________________________ When the going gets tough, the tough use duct tape.
I believe MC has the appropriate answer. The difference in drag between having the larger container on top or on the bottom is basicically insignificant.
I also suspect that most containers "cube out" before they reach their maximum weight - so relatively speaking, they aren't that heavy. If weight is a factor, they may try to put them on the bottom.
Carl will have more to add, I'm sure.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Evening Larry thanks for correcting me. I just thought that might have something to do with it. How does a shorter container bolt onto a bigger one without sliding off? After reading MC'S post again It makes perfeact sence!!! duhh me!
That makes sense about well size.
At first wells were uniformly sized for 40-foot containers, but subsequently, cars with wells for 45- and 48-foot containers were developed. Engineers are currently working on a design for a 53-foot double-stack car to fit within the present clearance diagram, but many existing cars can handle 53-foot containers on top of shorter boxes inside the wells. (from this link: http://www.trains.com/trn/default.aspx?c=a&id=219)
Maybe it's that I"m looking for a magic answer, but I seem to remember seeing occasions where the top (longer) container could have fit in the lower position of the well car. Also, I saw this configuration in shipping yards, where well length is not a constraint. (My shipping yard experience is limited to a 1-day tour, so I'm not pulling from too much information there)
Thanks so much for your replies. I'm interested in learning more about the wind resistance angle. Drag consumes so much loco fuel!
bubbajustinEvening Larry thanks for correcting me. I just thought that might have something to do with it. How does a shorter container bolt onto a bigger one without sliding off? After reading MC'S post again It makes perfeact sence!!! duhh me!
If you look at the longer containers, you will see that the main vertical posts are not at the end, but set in so that they arethe standard 40 feet apart. These posts have holes at the top and bottom which are used by the toplifters transferring and moving the containers around at the intermodal yards. Interbox Connectors are clever little devices that will hold the stacked containers together, and use the same vertical posts and holes. Look very carefully and you can see the very thin short handle of the IBC sticking out between the containers.
When there are 20' containers they will always go on the bottom level where the guides on the railcar will keep them in place. If they were on top of a long container there would be nothing to hold them at one end. I suppose it might be possible to double stack two pairs of 20' containers but I don't recall seeing that happen.
John
Ok I will have to look for that the next I'm trackside. I remember seeing the IBC on Extreme Trains. I do sometimes see 2 20' containers on trains. If you aren't carefull it look like one container. Thanks for that clarafacation.
Keep in mind that most container cars were designed to handle one 40 foot or two 20 foot containers in the bottom well.
These sizes were the defacto standard for a long time…then a bright engineer came up with a 53 foot container with the support post 20 feet either side of the center line which allows the larger container to sit on top of the other two then current designs.
You can have a 40 foot on the bottom, with a 53 foot on top, or a pair of 20 foot containers on the bottom, with the larger one on top.
The older container ships have the hold racks designed for 40 feet, which allows two 20s or a 40 foot to stack in racks below decks.
The 53 foot containers usually get deck stacked simply because they don’t fit the hold.
The 53 foot container is, relatively speaking, new, and it will take a little while for the railcar industry to build cars to fit…after all, the 40 foot container cars still have a lot of service/revenue years in them, so why replace them until you have to.
23 17 46 11
If one looks through Maritime trade publications, when they discuss container ships and their capacity the unit of measure is the TEU. The TEU is Twenty-foot Equivalent Unit. The 20 foot container is the basic unit of measure. The structural parts of containers are based on a 20 foot unit.
Stack cars have appratus that lock in multiple 20 foot containers on the bottom of the stack, that let the top stack be populated by additional 20 foot containers, a 40 foot container, a 48 foot container or a 53 foot container, as all the containers 40 foot and larger have their structural end posts at the 40 foot mark.
One observation from too much time on the Interstate...all containers have a similar weight capacity, despite their differences in size. The limiting factor is the maximum weight that is permitted in the highway system, both in the US and other countries.
Never too old to have a happy childhood!
The above answers have pretty well "nailed it".
You may also want to look at Ernest H. Robl's "The Intermodal Container FAQ" web site at:
http://www.robl.w1.com/Transport/intermod.htm
Specifically, the "Movement By Rail" page at:
http://www.robl.w1.com/Transport/intermod.htm#Movement_by_Rail
- PDN.
You'll rarely see anything other than 20-foot or 40-foot containers in international service, for the reasons cited by Ed. However, domestic business has long since outgrown 40-foot trailers, so domestic containers came in 45-foot and 48-foot lengths to keep up with the truckers' own trailers, and when 53-foot trailers showed up on the roads, the 53-foot containers were not far behind.
The original double-stack container cars for APL were all built with five 40-foot wells. You'd see them with 40-footers on the bottom (two-20-footers in the end wells, because those were the only ones that could handle the added weight), and either 40-foot or 45-foot boxes on top. Well cars later expanded, first to 45-foot wells in the three center positions, then to 48-foot center wells. Somewhere in there, the trucks in all positions except the ends were increased to 125-ton nominal capacity, permitting heavier loads, and the possibility of putting pairs of 20-foot containers in the center wells. Eventually, container weights outstripped these cars as well, which is why you'll sometimes see single-well cars, or drawbar-connected cars in sets of three or four units.
When 53-foot containers came along, they were not capable of being used anywhere on containers with the 40-foot wells, because there was not enough room between the wells (45- and 48-footers can fit, using the space over the trucks). So, stack cars with 53-foot wells appeared (yes, they're out there!). And, amazingly, there are some 56-foot wells in service, too (these are intended to handle pairs of 28-foot "pups", commonly used by UPS--they can handle containers of other lengths on the top layer, but only with a special adapter between layers). Most well cars have the length of the wells stenciled prominently on the side--if you don't see a number, you can assume that you're looking at a 40-foot well.
So here's the thing: why put longer containers on top? Consider: If you have the shorter ones to put on the lower level, and also longer ones, you can use the space above the trucks for the longer boxes' overhang, while keeping the train length shorter and improving the aerodynamics of the whole train. Shorter trains fit into more sidings if necessary, improving overall operations. Better aerodynamics decrease fuel consumption. Both of these are big contributors to the bottom line.
These factors have been influential in recent stack-car acquisitions, many of which have been cars with 40-foot wells, including cars of fairly early designs. But not only that--cars with 48-foot wells are being rebuilt to shorten the wells to 40 feet, shortening train length for trains that are used for international containers.
Carl
Railroader Emeritus (practiced railroading for 46 years--and in 2010 I finally got it right!)
CAACSCOCOM--I don't want to behave improperly, so I just won't behave at all. (SM)
CShaveRR You'll rarely see anything other than 20-foot or 40-foot containers in international service, for the reasons cited by Ed. However, domestic business has long since outgrown 40-foot trailers, so domestic containers came in 45-foot and 48-foot lengths to keep up with the truckers' own trailers, and when 53-foot trailers showed up on the roads, the 53-foot containers were not far behind. The original double-stack container cars for APL were all built with five 40-foot wells. You'd see them with 40-footers on the bottom (two-20-footers in the end wells, because those were the only ones that could handle the added weight), and either 40-foot or 45-foot boxes on top. Well cars later expanded, first to 45-foot wells in the three center positions, then to 48-foot center wells. Somewhere in there, the trucks in all positions except the ends were increased to 125-ton nominal capacity, permitting heavier loads, and the possibility of putting pairs of 20-foot containers in the center wells. Eventually, container weights outstripped these cars as well, which is why you'll sometimes see single-well cars, or drawbar-connected cars in sets of three or four units.. When 53-foot containers came along, they were not capable of being used anywhere on containers with the 40-foot wells, because there was not enough room between the wells (45- and 48-footers can fit, using the space over the trucks). So, stack cars with 53-foot wells appeared (yes, they're out there!). And, amazingly, there are some 56-foot wells in service, too (these are intended to handle pairs of 28-foot "pups", commonly used by UPS--they can handle containers of other lengths on the top layer, but only with a special adapter between layers). Most well cars have the length of the wells stenciled prominently on the side--if you don't see a number, you can assume that you're looking at a 40-foot well. So here's the thing: why put longer containers on top? Consider: If you have the shorter ones to put on the lower level, and also longer ones, you can use the space above the trucks for the longer boxes' overhang, while keeping the train length shorter and improving the aerodynamics of the whole train. Shorter trains fit into more sidings if necessary, improving overall operations. Better aerodynamics decrease fuel consumption. Both of these are big contributors to the bottom line. These factors have been influential in recent stack-car acquisitions, many of which have been cars with 40-foot wells, including cars of fairly early designs. But not only that--cars with 48-foot wells are being rebuilt to shorten the wells to 40 feet, shortening train length for trains that are used for international containers.
Ask, and thou shall receive!
Y'all get partial credit, but not full credit. Length is an issue sometimes (i.e. can't put a 53' box in the bottom well of a 48' car - this is true), but you're forgetting about width. That's now the bigger reason.
Often you see a 53' box on top of a 40 or 45' box - in a 53' well. Why isn't the 53' on the bottom and the 40-45 on top? Because the 40 or 45" is too skinny to be on top.
ISO boxes (International boxes (20-40-45) are narrower than domestic boxes (48' - 53'). ISO's are 96" wide, whereas the domestic boxes are 102" wide. Herein lies the problem. The newer 102" wide domestic boxes have their roof apertures as far outboard as possible, just inside of the exterior wall. This is done so that the lifting force of picking up that box tranfers directly to the sidewall, instead of transferring through a roof member to the sidewall. Older domestic boxes had them further inboard, but this wasn't a good lifting solution. A set of IBCs on top of a newer domestic box is too wide to accept an ISO box on top. The ISO box would sit inside of the IBC's (if not fully, at least partially). However, if you look at the bottom of a domestic box, it has 2 sets of aperatures in the bottom of the stack frame. One is at the width of an ISO box, the other is at the width of a domestic box. That way the domestic box can go on top of either an ISO or another domestic.
So, you can put an ISO on an ISO, you can put a domestic on a domestic, you can put a domestic on an ISO, but you can''t put an ISO on top of a domestic.
Drag plays a part. I remember reading that the smaller the gaps along the tops of the containers the less the drag. Makes sense to me. Is it a big enough difference to matter? It may depend on the length of the train. You look at one of those superlong double stack trains we saw back during the shipping boom, and it might really matter.
Jack
Geez, I though we had the answers yesterday, and then Carl and Doublestack show up and add even more really good information ! Thanks, guys !
Just amazing - someone could edit this thread to tighten it up some, and then have a heckuva technical article on this subject. I've never seen so much on this subject in a single place before !
I thought it was interesting how Carl relates that regardless of how big the capacity of the trucks under the well cars have been upgraded to, the loads still seem to outstrip them. But I've never before read about cars being shortened to make them more functional as the system evolves - lengthened and made bigger, yes, happens often - but not shorter. Just goes to show how driven the rails are to wring each bit of inefficiency out of that system. Wasn't it the old Southern Railway that had the slogan, "We take the waste out of distribution" (or similar) ?
Also reminds of a quote from a management book I like: "Man is by nature a complicating animal. He simplifies only under extreme pressure." The proliferation of first lengths and now widths, and the many possible combinations of same, illustrate that quite well. But it all works, as long as there are intelligent people on the ramps, I suppose.
Thanks again for the excellent and well-written info.
- Paul North.
Ah ha! Doublestack, I think you had the magic answer I was looking for :) I had no idea that domestics had a two sets of apertures on the bottom only. That's great design - it encourages both the shortening of the train and reduced wind resistance while simplifying the container's construction (not necessary to build two sets of apertures on top *and* bottom). Earlier today I saw a 53' on top of a 40' in a 53' well and stood there scratching my head. Now I'm just excited to get it.
Wow - thanks to everyone pondered and wrote such fantastic explanations. You guys rock!
Yah there are some really knolagable and freindly folks around here.
bubbajustinYah there are some really knolagable and freindly folks around here.
Yah this machine doesn't have spell check. Welcome to the forum!
Claire Ah ha! Doublestack, I think you had the magic answer I was looking for :) I had no idea that domestics had a two sets of apertures on the bottom only. That's great design - it encourages both the shortening of the train and reduced wind resistance while simplifying the container's construction (not necessary to build two sets of apertures on top *and* bottom). Earlier today I saw a 53' on top of a 40' in a 53' well and stood there scratching my head. Now I'm just excited to get it. Wow - thanks to everyone pondered and wrote such fantastic explanations. You guys rock!
So if the 53 ft. long that Claire saw earlier today (above) was a domestic box at 102" = 8'-6" wide, and the 40 ft. long box underneath was an ISO box at 96" = 8'-0" wide, then the 53' would overhang the ISO by about 3" on each side, and by about 6'6" on each end, correct ?
Hi Paul,
Yes they would overhang about as much as you calculated. These photos (especially the 3rd) show a bit of that effect.
http://www.matts-place.com/intermodal/part3/images/snlu954515.jpg
http://www.matts-place.com/intermodal/part3/images/snlu977733.jpg
http://www.matts-place.com/intermodal/part3/images/snlu982020.jpg
Next time I get out on the yard at work, I'll see if I can snag a photo of the double aperature under the boxes. Its a pretty cool casting. One thing related to the casting that most folks will never see is an IBC hung up under a box. Sometime the mechanism (rod) that turns the 2 bayonettes on the IBC gets twisted and the IBC hangs onto the bottom aperature of the top box. It can hang there even after the box is on a chassis. If a driver isn't careful, he can leave the rail ramp that way and get on the street with that 13 lb steel monster hanging there and waiting to drop. I know of 2 instances where that happened. 1 resulted in a fatality, the other just vehicle damage to a following van.
I get my donut $ helping make those big boxes move, so I have a little extra access to equipment and insight.... hence the handle.
If one pays attention to the train that starts moving toward the camera at 2 mins 30 sec into the following clip, you will see a variety of stack mounting....including one of a 53 foot on the bottom and a 48 foot on top.
http://www.youtube.com/watch?v=Nrgg76f_lQQ
This
BaltACD ... you will see a variety of stack mounting....including one of a 53 foot on the bottom and a 48 foot on top.
... you will see a variety of stack mounting....including one of a 53 foot on the bottom and a 48 foot on top.
Great couterexample! I've never seen one. It makes sense because the 53' and the 48' are both domestic.
Exactly right Claire - both domestic.
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