USING RESIN FOR UNDERWATER DIORAMA

I've looked at this issue before and would not recommend doing this. It's expensive first of all. It takes a lot of pours, 1/4" at a time. One bubble and you are in trouble.

Other strategies work better IMO, such as a surface plate with the model suspended beneath it.

Bill

Consider the material cost.  Smooth On makes a deep pour clear epoxy resin.  I have dealt with smooth on and they make a good product.  On their site they have a material estimator. Using your dimensions, and assuming that you made a typo of 12 feet as opposed to 12 inches, the material needed for 5.5"x5.0"x12" is approximately 180 fluid oz.  You will require 5+ gallons at about $160 dollars per gallon.  This does not include mold boxes or other accessories.  

Note the cautions about an exorhermic  reaction

EdGrune

Consider the material cost.  Smooth On makes a deep pour clear epoxy resin.  I have dealt with smooth on and they make a good product.  On their site they have a material estimator. Using your dimensions, and assuming that you made a typo of 12 feet as opposed to 12 inches, the material needed for 5.5"x5.0"x12" is approximately 180 fluid oz.  You will require 5+ gallons at about $160 dollars per gallon.  This does not include mold boxes or other accessories.  
Note the cautions about an exorhermic  reaction

GMorrison

Other strategies work better IMO, such as a surface plate with the model suspended beneath it

What I have seen:

 So Pour your colored resin in a 1/2 inch layer on all four sides. Then use textured Plexi for the top shaded in the colors you need there. Your boat will be near the center right? Well, all four sides and the top cover will not give away the emptiness within.

     The biggest trick is to make sure your corner pours are rounded within, No seams them.

This is basically what I have.  It's an upside down display case for a car.  The base of the case would go on the top where the two boards are holding the depth charges.  That section is recessed and would hold about 3/8" of colored resin.  I see where you're going with the 1/2 of resin on all 4 sides, but I believe that would require 4 sections of plexi.  I decided to use this case instead 

Time to check what the model railroders use:  Woodland Scenics water products.

fuzznoggin

Why 5+gallons if I only need to fill 1.5 gallon tank?

Brobably a math uh-oh (happens to us all).

I'm getting 330 cubic inches, or 1.428 gallons [5.407 litres]. 

You are still looking at US$150-200 of resin.

I'll wager that's an acrylic case and bottom--so, you really need a second, potentially sacrificial, example to see if your selected resin reacts to it.

Pouring inside a clear box introduces an issue of bubbles or film effects against the inner surface, whic hwould be largely irreperable. 

From watching some of the "large pour" you tube channels (like minibricks or thassalo) they invariably peel away what ever form work is ues so that they can polish the cast surface with any number of acrylic polishing compounds.  And, even then, they often use a clear acrylic gloss spray to finish them.

So, yes, probably a better idea to create a clear "water surface" and suspend all that careful work , and let the observers' eyes "fill in the blanks" for ocean effects.

I'd resist depicting a sea bottom on the base of hte case--average ocean depth is near 2000 feet (600-700m).  Average WWII crush depths were in the 300'/100m sort of range.  60 fathoms (360'/109m) is still considered "dangerously shallow" waters for submarine operations--just too easy to use the bottom a"against" the sub.

Immersing a stryene model in a large pour of resin is problemmatic.  Resin heats up as it cures.  If you pore all the resin at once the heat may deform the model.  You would have to pour in very thin layers.

Cap'n Mac said "Average WWII crush depths were in the 300'/100m sort of range."

I usually visualize it as max. depth = length of boat, in that era.

Bill

I discarded the idea of a solid resin pour for my underwater submarine scene, for all the reasons mentioned above, and settled on using an Imex display case and suspending a layer of plastic most of the way up that I've put a layer of acrylic gel medium on to simulate ocean waves. I hope to tint the clear sides with some light blue transparency film I picked up at Office Depot. This is another one of my bazillion works in progress, so no pics yet.

Imex display case no. 2513 is for figures, the company says, but at 4 1/2-inches square and 8-inches high, it's just right for a 1/700 US submarine on the ocean floor and a Japanese sub chaser suspended 200 scale feet above it. I don't think Imex is still in business but you can find their cases on eBay.

Something to consider for the underwater wakes from propellers and depth charges is an idea I saw a guy on the Armorama website use - plastic cling wrap (Saran wrap) twisted into a cone shape. It looks pretty convincing when glued in place behind a prop, or twisted into a narrow spiral for the wake from a sinking depth charge.

Everyone's ideas were great, and I thank you.   I've waffled back and forth on how to do this.  Then I went back to YouTube and watched some of these pours, some of which looked like 2 gallons of resin all poured at the same time.  They made it look easy, and frankly the pouring was.  It's what happened 6 hours later.  A few areas of the paint along the side of the sub started to peel.  Some of the cotton did weird things.  

Then the bubbles started out of the bow and stern sections which were sealed off with Apoxie Sculpt.  Not that I was that concerned on bubbles because it would be apropos for the setting.  Later last night there was a spew of air out of the bottom of the sub that looks like mercury ran out and laid itself on the bottom.

Frustrating for the first time.  Probably the last time as this wasn't a cheap experiment.  Not mourning the model or case as that didn't cost more than $25 combined.  It was the $79.00 Liquid Glass resin that was supposed to be able to be poured at 4" depths per their literature.  They did say it would get warm and even after setting it under an A/C vent with a fan it still got relatively hot.  I can see where smaller pours would be beneficial but with tinting, it would be very difficult to match - resulting in visible layered sections in my opinion.  I'll try to dress up the surface with Acrylic Medium and see how it looks afterwards.   I might be able to convince that the air spew at the bottom was a result of the first second of the explosion. 

To tell you the truth though, I really wish these YouTuber's would spend their energy on listing the type of resin they are using on these massive deep pours (tinted also) instead of listing their musical scores used in the video.  I've inquired with at least 6 Tubers on what type of resin they used and heard nothing back.  Trade secret perhaps, who knows.

If I do another unerwater diorama, and that is a big if, it will be as others had recommended; simulated ocean top and no resin in the tank.    

I have the impression that many of these YouTubers who do things with epoxy are performance artists with little actual understanding of things like chemistry and exothermic reactions. My

Fuzznoggin, never give up!!! I did a diorama of the USS Hudson sinking the I-171 in a resin block. It took me nine months of experimenting, and I failed several times. In fact, I built the sub 4 times and the destroyer 3 times before I had success. However, the results were amazing when I finally got it right-and you will! My work was published in FSM April 2017 in an article entitled "Death of the I-171".  The article covers all the steps I took to have success. It was a bold project you took on, and you will have succes eventually. You've already accomplished the hardest step-just showing up! That's my favorite quote from Will Rogers-"Half of anything is just showing up!". Good luck, Luke Easter

Crush depth was around 250m to 300m (800' to 950') for type VII boats according to Wikipedia and other such sources.

polystyreneaddict

Crush depth was around 250m to 300m (800' to 950') for type VII boats according to Wikipedia

That has to be a units transcription error.  Getting to a hundred fathoms (600' / 182m) was a huge deal for US WWII subs.

Submarines in WWII had a huge number of through-openings for mechanical linkages, air and seawater plumbing, and the like.  These were not easy vessels to "pressure proof."

For perspective, it was a very huge deal when the Soviet Alpha subs tested down to 400m (past 1200' keel depth) in the 70s, 25 years after WWII and requiring major tech leaps in maching titanium.

US depth charge depth settings were 50', 75', and 150' during WWII.  Part of that was in the time required for the DC to drop to that depth and the relative motion of the target.

Sometimes you get lucky, sometimes you have epic failures.  I didn't want to show this but this is an example of epic failure in my book.  The pour really didn't look that bad at first.  Then the next morning there was this spew of air spread along the bottom and up the sides.  Almost looks like Mercury.  

The surface isn't quite finished yet, but I decided to try to dress it up ( lipstick on a pig ) somewhat to keep me from wanting to toss it in the dumpster.   Yes, I should have heeded the words of Capt'n Mac and only did a surface resin display on the tank.  Curse you "YouTube" for enticing me to push the envelope and doing a deep pour.   Never again.   The loss of the 1:350 u-boat model is minimal compared to the cost of the gallon of resin used.  

I'll do occasional dio's using resin, but they will be strictly surface pours - no more submerged stuff.   Live and learn.

Pfffffff .... you don't have anything to be ashamed of, mate. I think it looks kind of cool, otherwordly, and something to keep on the shelf. But that's just me.