Kahlenberg are top end. I have a set of D-0's, they're loud! I originally purchased K-380's, a smaller horn, smaller compressor. I did not like them. Plenty loud, but sounded like a car horn. A friend stopped by and of course had to blow them. "Hm", he says, "sounds just like a car horn".
Kahlenberg took them back, gave me full credit, and a special discount on the D-0 kit which required a different compressor. Dealing with them was a real pleasure. A year or two later, one of the trumpets started to discolor, I called and asked what I could do with it, guy on the phone says "oh, they shouldn't do that, I'll send you a replacement, just ship the old one back when you get it." No charge, no shipping on the replacement, I was happy to pay the return shipping.
They are top quality, not cheap, but they work. I made the mistake of blowing it when my wife was on the foredeck. She's jumpy to start with, I got a withering glare and a real earful when she came back in. I won't repeat that misstep. They are LOUD.
A guy who owned a Florida Bay Coaster had a full size ship's horn on the pilothouse roof, couldn't see it from the water. It was the ultimate attention grabber, the reactions were priceless!
For less $$, I think the truck horns are a great alternative. I really wanted to put a pull chain on mine, but the mounting wasn't practical. Solenoid works just fine. I had electrics before, what a maintenance PITA.
