If i was sponsored by Futaba (dont care how big or small of a sponshorship it is...its still a sponsorship) i guess i would do what they tell me to do too.
You really, truly believe this is why I am saying this??
Well then consider this. They make a number of servos that they list as 4.8 volt only. I tell people, no worries, run at 6 volts I do all day long (9255 for instance).
They have other servos that they say Nicad only. I tell people, no worries use NiMH or even lithium packs (regulated to 6 volts).
So you'll have to base your desire to reject my advice and that of Futaba on something more concrete than the fact that I wear their shirt.
While they strongly recommend "NOT" to keep the antenna in a horizontal position....why cant we get anymore to the reasoning other then line of sight. Ive seen these systems used in mono's that were so tall, the antenna was STILL under the deck and cowl... which puts that "line of sight" straight out the window into the storm gutter on the corner.
Well, you see, it's called "physics". Futaba did not make it up. Radio frequency wavelength at 2.4 GHz is very short and can easily be attenuated by solid physical objects like engines, pipes, big batteries, fuel tanks, etc. So anything you can do the optimize the installation to minimize that possibility is a good thing.
Secondly, the radio signal is what is called "vertically polarized". That means the optimal antenna orientation between the 2 antennas (TX and RX) is vertical. Again, this is not a Futaba design thing, it is an absolute fact of this type of radio transmission.
Many airplane installations cannot get the antenna outside the fuselage (40% aerobatic planes for instance). But they install the RX in positions that maximize the orientation for the antennas. Many put the RX high in the fuse so the antennas are close to the fuselage. And those receivers use two external antennas which make certain that at least one of them "sees" the TX antenna all the time. And they are installed at right angles to each other to maintain the vertical polarization orientation between the TX and RX as much as possible.
And last, 2.4 GHz wavelength will penetrate fiberglass without a hitch, so the example you cite does not apply. If the hull was made of CF or there is a CF pipe in the way, that signal will have significant problems.
Like I said, people are free to do what they want to. Nobody can stop you from that. But there is no sound technical justification for doing anything other than installing it as recommended.
While running it horizontal may work, it is also more likely to have issues as opposed to the recommended installation. It does not say you will absolutely have a problem, just that it is a higher probability event and I for one and not willing to take that bet with a big fast boat.
But like you say, I wear their shirt so this is likely nothing more than the party line. But ask yourself, if it truly did not matter, why would they recommend it in the first place??
FWIW I run the FASST system in 7 FE boats and one gas cat. All my antennas are installed vertically. And so there is no confusion at all I am on the Futaba Air Team and not the Marine Team.