Steam Packet drops daily LPL service from Nov9 til next March, and weekend sailing times on the slower ship (as opposed to fast craft) preclude day trips. North West bound travellers have fewer options so air pax numbers should rise.
If IoM Airport serious about increasing North West bound loads they should be seeking to get Treasury to pass on IoM APD to them to reduce/remove pax handling charges etc. Fat chance though. And anyway that would really get the greens twitching!
Or maybe level the playing field by imposing an APD equivalent on ferry pax? That would add a good few pennies to the Treasury coffers...