In a raft bed, most people use a net pot or slit pot (small plastic basket kind of pot) for the plants and a variety of media can be used in the pot to hold the seedling. However, there is only minimal support for the plants in little net pots in rafts so most people stick with growing smaller faster crops this way since much effort would be expended to help support taller crops.

What kind of Coir would it be? There are a variety of "grades" and some will be almost like peat and tend to stay too wet and decompose while others will be more like fiber and yet other might be more like the nut shell chips.

If a goal of the system is to use what is abundantly available on the island, you will want to do some research into designs that use intermittent flow or grow plants that won't mind the boggy nature of some coir products.

Some possible issues with coir include;
too wet
decomposition
turning the water brown
lowering pH
salt from washing in sea water

All the above possible issues may vary considerably depending on the particular product and preparation used. Do some extra research to decide if the stuff will work for you.
I believe Michael Cosmo is still using a coir chip type product in his vertigrow stacks. There are others who husk their own coconuts and use the husks and fibers in their systems. Unfortunately, you might not get as much help with using coir since not as much research into using it for aquaponics has been done (because of many of the above listed problems) so you would be doing your own Research and development to an extent.

Tomlin, your aqritourism farm sounds exciting, but I think you might want to reconsider using coir in an aquaponic system. You want to avoid anything that will decompose. I just wrote an article for Growing Edge about media you may find useful and there are some discussions in the forum section here about Media as well.