Hi Frank and Angus.
Well, as the author, I stated very clearly in the accompanying file that the horn sounds are not intended to be genune.
They meet the IMO requirements for pitch against vessel size. The rest, such a leaky feeder pipe to one of the horns in one vessel, and so on, are fabrications. But none are unrealistic.
Fred and I spent a lot of time locating original recordings where possible and recordings of similar types of vessel where the ship itself is imaginary. I was not going to break someone else's copyright by just slapping those sounds into a pack (the recordings were all pretty poor anyway), so I fabricated similar sounds, with ultra-high quality. I used a full 32-track studio to create and mix the sounds.
I even got a couple of recordings from the real vessels while they were in the Solent, thanks to obliging captains. In the radio pack, you can hear one captain asking QHM for permission to sound the horn for me!
And still the nit-pickers moan....