HI Ralph
I was using 3mm white LEDS in the lower Portholes on the Olympic. Ended up having to seal all the lower portholes with resin dropped over each Led in situ. At 100 scale the effect looked ok but for larger scales you would need to provide a solid waxed seal on the outer (flanged) side and pour the resin in from the back of the porthole - I'm assuming a flanged tubed porthole. I guess your clear plastic discs performed this function in your case.
Cheers 😀

HI Dave
Yes I got round that by using clear resin on the inside after lightly fixing the glazing, that way I had a flush and flat looking plastic port on the outside of the hull and waterproofed on the inside. Using just resin tended to be concave. A lot depends how easy it is to get to the inside of the port I guess.

HI Ralph
Yes have tried this method. OK for statics and portholes above the water line. No good for anything near the waterline - they leak! My Olympic has a whole row just above the waterline, using clear resin was the best option.
Thanks for the input 😀

Hi
See how I used circular punch to create clear plastic ports - Refer to Photo Gallery & Anything Else for full details.

HI Dave, it is a 2 part epoxy substance which creates a crystal clear solid Illusion of deep water manufactured by Deluxematerials.com.Takes a long time to set but is very effective. I thought it would look good for windows but it appears to be more trouble than its worth. it also dissolves Plastic magic glue so beware!

HI Seafarer
What exactly is "solid water"? I am familiar with water clear epoxy resin, commonly used for encapsulating flowers and other specimens. This can be used down to a min thickness of 2mm and once set is Impervious to water and remains clear. You can read about it here http://www.tomps.com/shop/water-clear-epoxy-resin-21-p-248.html. A clean sheet of glass behind your windows while the resin sets would provide the backing.

I have used this type of stuff on my model railway layout, but be careful as if this stuff gets wet, it goes opaque and does NOT remain fully clear. Can you not simply cut some window panels out of clear styrene sheet?
I found this out when I went to "dust" the water areas with a damp cloth, so how long it would last when subject to getting wet for longer periods is anyones guess.

You could always try a "test piece" first of course, but remember to test it in a sample of the water your boat will be sailing in, not just ordinary tap fed water, it does make a difference.