RRS 49.1 regulates the position of the crew. In this rule it is permitted to use a "device" to position the body outboard, as long as this device is not specifically designed for it. (With exception of hiking straps and stiffeners worn under the thighs.)
For instance the jib sheet or the main sheet. Both designed to work the sails, not for hiking, therefore they may be used for that purpose. Then there are control lines, for instance the vang control line or the traveler control line. Can they be used for hiking?
What do you think?
Philippe Presti racing against Torvar Mirsky in the semifinals. Calpe, 12 April 2008. Photo copyright Pierre Orphanidis / Valencia Sailing
In Calpe I learned a good way to answer this question.
If the control line can be adjusted from the position the crew is in, it complies with rule 49.1. The line is in use to adjust the - in our case - vang or traveler. The fact that this may be infrequent, is not relevant, it still passes the test for 49.1. While hiking you can adjust them, same as the main sheet.
If that same vang control line cannot be cleated or uncleated from a hiking position, it is no longer a control line, but at that moment something specifically in use to project the body outboard. In that case the use of that same control line, breaks RRS 49.1.
When, confronted with a new boat you are not sure, find a crew when they are not racing and ask them to show you. Or ask members of the team who are more familiar with the boat.