Alternative for resins

I suggest you not use clear silicone sealant for waves. It's messy and smelly and shrinks a little when it sets.

I agree with the plexiglass surface.  I did similiar, in a much smaller size (8" x 10"), a while ago for a scene with SEALs in ODS (Op Desert Storm, '91).  I glued the SEALs under the plexi to the floor, which was about 1" below and painted a sandy brown color for the bottom.  Then placed the plexi surface and tinted it blue-green with clear colors.  The boats (waterline, not extending below), floating bottle, dock, ect. were then added on top with a few small wakes added from 5-minute epoxy.  Excuse the crappy pic, it was taken with a cheap digicam a long time ago (need to update them as I still have it).

The OP has posted that he intends to make the becalmed USS Constitution being kedged along to escape the pursuing British fleet.   His scale choice is 1:96.  He wants to see the full hull presentation

Some thoughts:

In 1:96 the draft depth of the model will be close to 3 inches.   Making the box depth 3 inches will likely putting the keel on or near the bottom of the display.  Add a half-inch or more for a more convincing display, not resting on the bottom.

Casting resin, particularly clear resin heats while curing.  Pouring resin "water" in lifts much beyond 1/4 inch, especially in the box size you envision, will create a significant amount of heat which may warp the plastic.    The more resin - the more heat.  Clear casting resins also often contract after curing.   As you pour your lifts, particularly the last one, the water surface will appear to defy gravity and climb the hull sides.

I still think a plexiglas box is still the way to go.   You don't need the 6th side, the bottom.   Make it so the box fits into a decorative wooden base.  Adjust the four side pieces to the desired depth.  They may be lightly sprayed with a clear blue or green to help with the oceanic appearance.  The top side is the ocean surface.  Cut holes in this piece to accept the ship and long boats.   Attach them to the surface piece with some clear acrylic artists gel medium.   Sculpt some surface waves too, but not much.  Becalmed = glass smooth sea description.  Tint the surface with more artists acrylic paint + gloss medium.   Less is more.

GMorrison

Not a direct response to the OP, but there are some really awesome sea dioramas being shown in Asia where the sea surface is a horizontal digital display that has an active wake. 

Yeah, there is a lot going on in scale modeling in Asia, that I think we don't really get to see, and vice versa.  The Internet has made both communities more accessible, of course, especially via sites like Facebook.

As far as modeling an underwater diorama in resin goes, have a look at Won-*** Lee's work at ModelWarships.com.  He has made some outstanding dioramas.  To the original poster's question, and contradicting my own reply, I think this particular diorama of a German sub is cast in a block of resin, though I may be mistaken.  Either way, his dioramas provide proof of concept for this particular genre.

http://www.modelshipgallery.com/gallery/ss/dkm/Type7c-350-whl1/index.htm

PS-taking a closer look, I take it back, I don't think it's a solid block.  I can see the sides extending up above the wave line.  Though, it still could be that it's cast within a plexi box.

He did another diorama of a sub under depth charge attack, showing the explosions, with the sub chaser on the surface.  If you browse his gallery there, I think you can find it.

Not a direct response to the OP, but there are some really awesome sea dioramas being shown in Asia where the sea surface is a horizontal digital display that has an active wake.

Waynesbea

...I am sure this question has bee asked before.

I plan on making a ocean diorama, which I have never did before. The dimensions are 22"" x 44" x 3" deep. That is over 12 gals. of resin... 

Actually, in that particular form, I don't think anyone's ever asked this before.

As was pointed out, you don't need to cast a solid block of resin, it would be easier to make a box of plexiglass, with a top depicting the ocean surface. I think it'd be far easier, than casting a cuboid in resin (had to look that up-I could only think of "cube", but yours won't have 6 faces that are squares of the same dimensions).

Bill

I am courntly building the USS CONSTIUTION in 1:96 scale and plan on  showing her in full sail. Druing the war of 1812 she was beeing chased but the Royal Navy off the coast of N J and there was no wind, so they put out there small boats to Kedge the ship so it was not at a stand still 

I guess I could make the ocean just around the boats and not the whole base board..

Wayne

Original post tells you what you really know.

And it'll weigh 100 pounds or so.

Its a big dio. If you want to share the details I/we would be happy to offer specific suggestions.

Either suggestion above is a good one, the point about being able to see under water is a decisive one.

Bill

Does it need to be solid resin?

plexiglas ain't cheap but it may be cheaper than resin.   Build a 6 sided box of plexiglas and use resin on the surface to fair-in and imbed the surface models/details

Do you really need to see below the surface?  If not, you can use a sheet of plywood and acrylic gel medium to build up the wave action.  Once painted and heavily glossed, it replicates an ocean surface well.