'A device is an object that has been invented for a particular purpose' Collins Dictionary

In terminology a “boat” is “a sailboat and the crew on board” and a “competitor” is “a person who races or intends to race in the event”
I think both of them effectively describe human beings and their interactions with a boat so don’t see how they could be described as a device. 
As Gordon has said, the dictionary gives a pretty good steer also. 

That sounds correct, as according to case 4 in the casebook a competitor's may hold a sheet outboard while a device may not.

RRS Terminology states that other words (not defined in RRS) are used in the sense ordinarily understood in nautical and general use.

World Sailing Constitution 2.3 states: All official Federation English texts should be edited to comply with what is known as “Plain English”
in the United Kingdom.

This can be an issue when discussing the rules with speakers of other forms of English, or closely related languages. It also means that RRS 47 is in breach of WS Con 2.3 - because trash, in this context is a US English alternative to the the UK English word 'rubbish'!

As usual ERS uses a different wording from RRS - ERS defines a 'fitting' as an ' item, including any associated fitting, that is not part of the boat
structure but is bonded or fastened to the hull, hull appendages or rig.

ERS C.5.2 Personal Equipment also defines personal equipment  as:
All personal effects carried or worn and items worn on board to keep warm and/or dry, and/or to protect the body, personal flotation device, safety
harnesses and hiking aids worn to keep the person aboard or afloat.

RRS 49.1 would be clearer if 'device' were replaced by 'fitting or personal equipment'.

Does this mean that a sailor should not be allowed to hike off the underside of the cutty cabin on a R19?
How about if a sailor falls in the water because their mainsheet snaps... does that mean they were using the mainsheet to position themselves outboard?
I was pointed to match racing call L3 to answer these questions. It's pretty clear that everything I asked about above is allowed.

Perhaps Alfred was contemplating the trapezing crew standing on the skipper's shoulders?
That is more a meme than a device.

 “No part of a person’s body is a ‘device’” according to WS Case 4, which refers to the word “device” used in RRS 55.3.

Generally, the interpretation of undefined words within legislation/rules takes the ordinary and natural meaning of the words used in that provision. The Macquarie dictionary is used at the highest level in Australia for this purpose.

Tongue in cheek for discussion: prosthetics, hearing aids, etc.…

Rene,
I wrote earlier:
 World Sailing Constitution 2.3 states: All official Federation English texts should be edited to comply with what is known as “Plain English”
in the United Kingdom.

This can be an issue when discussing the rules with speakers of other forms of English, or closely related languages. It also means that RRS 47 is in breach of WS Con 2.3 - because trash, in this context is a US English alternative to the the UK English word 'rubbish'!