While I thrash out the fine points of motion blur and caustics, I add volumetrics into the pot. I got the searchlight to work...after a fashion. It won't show up if pointed away from the camera. Why not? [That was my first choice] But it will show if nearly pointed at you. But the beam only shows when it crosses a physical object...like the hull, or, in various other shots, the hull and fish. Why so? The light beam is not falling on the hull at all. Why the gap?

Volumetric lights are editable as you have discovered. :]

However, it isn't enough to increase the intensity of a light. You also have to play with the colour, softness, falloff, lensflares, shadows/dust etc etc. The higher the value in the shadows/dust selection, the more intense the effect. (Be warned the rendering will increase drammatically). This also applies to other aspects of volumetric lighting. The higher the value the more intense the effect. Except perhaps with fall out values.

The intensity effects such as power, dust/shadow/lensflare affect the amount of visible light that 'light' will show in your scene; spread and fall off effects the length and width of the light.

Never be afraid to edit each and every setting available when choosing the right light for your scene, if you dont like it undo it, if that doesn't work, delete it and try again with a new light.

(I would suggest you save your scene first before applying radical changes, just in case you decide you have gone a little bit overboard or crossed over to the extreme side of editing)

A Personal opinion if I may: 400% is ok if that subtleness is what you are aiming for, usually 600% + is even better; sometimes even overlapping the light with another one, slightly different in colour, intensity, light gel, etc is better (depending on the effect you are trying to achieve) Layering elements can usually be more effective than relying on only one element to achieve one's goal.

Have you considered quadratic lighting? You have two types available to you in vue 4 ~ quadratic spotlight and quadratic pointlight (both volumetric). These may get you closer to achieving your desired effect.

Just a few idle thoughts that might assist. :]

kitten: I played with your suggestions, and while the quality of the light beam got better, it still won't cross the water. Note how it falls on the sub and the fish. But nothing in between. In the Volumetric Options, the Intensity is all the way up. Quality Boost is all the way up. Show Smoke/Dust is enabled and the S/D settings are up to [about] 5.0...so the question remains: why won't the beam cross open water?