Sea Wolf and Sea Dart: Unbuilt Derivatives and Cancelled Applications

[Mike Pryce]

Probably because the distance they can be seen over the horizon isn't as far.

Wait, that probably doesn't make any sense if you haven't had lookout training.

• Imagine a picture of a ship. The horizon is obviously behind it, and is probably even above the weather deck of the ship. Been long enough I don't remember the formal name for that. Usually called out as a distance to the horizon, "three-quarters to horizon," but if you remembered your horizon distance (based on how high you were up off the waterline yourself) you could guesstimate ranges pretty well.
• Now make it farther away from you, so you can still see all the way down to the waterline but the waterline is on the horizon. That's "on the horizon".
• Now make that ship even farther away from you, so that the horizon crawls up the hull from the waterline, say to the weather deck. That's "hull down on the horizon".
• Finally, make it so far away that the horizon covers up the superstructure and even the masthead. Completely out of sight.

The smaller the ship, the closer the distance between "Hull down on the horizon" and "on the horizon" is.

Wish I had the Paint skills to draw this out, it'd be a lot easier!

I used to watch ships along the English Channel from out the window of my old home. Odd to see containers moving along but the ship invisible.

My clutter comment was based on thinking at some distance only masts would be seen. Presumably they get lost in the clutter from waves, and that distance would be closer on smaller ships.

Without knowing the 909 radar height it's hard to know the distance to the radar horizon though.

 

[Dilandu]

Dumb question from me, but why is range shorter for smaller targets? Clutter?

The missile is semi-active homing on the radar echo from the target, illuminated by ship's radar. So the enemy ship must be visible above horizon. The smaller (and lower) the enemy ship is, the less distance from which it would be visible.