Keep in mind that this is a port during the '40's...water is probably very dirty and murky. Pollutants such as oil, diesel, etc. float on the surface therefore you probably couldn't see very deep - no more than a couple of feet. It was also nighttime so the water was dark. I'm not a big fan of clear pouring resin. What I usually do is place a thin layer (a couple of mm's) of Celluclay. Place the model in before it sets (up to a couple of days). I either waterline my model, or raise it up on thin styrene strips to compensate for the depth of the Celluclay - otherwise they will look like they are way too deep in the water. Paint the surface of the Celluclay whatever color you want the water to be. Then spread on several coats of clear liquid acrylic (it's thicker than varnish) allowing it to dry between coats (just a matter of hours, or overnight). A millimeter, or two, will give the impression of much greater depth. If you're going to build the Campbeltown after ramming the drydock doors, then you may have to saw off part of the rear lower hull at an angle, so that the bows are angled up and exposed.
Examples of clear acrylic over Celluclay:


You MUST paint the water color BEFORE applying the clear liquid acrylic for the illusion of depth. For the ships' wash and wake I stippled on thicker clear acrylic paste.
