Aaron, I don't want to start anything or say you are lying, but I have been behind a boat with only two 6x9's riding at about 65ft and you could sort of hear music, but not make out the words really. If you cut out the sound disappeared. I have 4 audiobahn 6x9's with horn tweeters (not real HLCD horns) but horn shaped to disperse the sound out to the sides. They are each recieving 125 watts RMS. I can hear them real well while directly behind the boat, but if its windy or there is other noise on the water I can't hear them very well when I cut out.
I have never heard NVS or WetSounds, but my friend has a custom horn setup built with two 22" horns haved down to 16 inches for tuning reasons, and two 8" mid bass woofers. To make a long story short, I hadn't been behind his boat in a long time and I was used to hearing my speaker setup. Well I went behind his boat and I couldn't believe I had forgotten how much LOUDER his stereo was. He got out behind the boat after me and said it wasn't sounding as loud as it usually does...it turned out only 1 horn and 1 woofer were working.
I guess botom line is that loudness is all subjective, and when you say you can "hear" the music with your speakers. I wonder what you think if you were to "hear" a pro audio setup. Don't take me wrong, I am not knocking your sytem in any way! I really think the design is cool and unique and it turned out very professional for you just doing it in your spare time. I gave my shot at building a box once and I scrapped that idea really quickly.
BTW- why didn't you want the box mounted under the tower and upside down? It seem that the arch would allow you enough room to walk through without hitting your head.
Also, sorry for the long post, I am studying for finals (well taking a little break) and wired on caffine