Depends!

All US Sailing run events... require wearing of a CG approved PFD. CG = coast guard. Some vests were recently added to the list (don't remember off hand what they are though)

State and fed law require you to carry a CG PFD (and perhaps a throwable if 16 feet and up and you are an adult. (so you need the throwable as well)

When you go racing at other venues. the US Sailing Prescriptions enforce that legal requirement as a matter of the RRS ... so its just like a sailing rule.

If they say nothing in the SIs... you can put your CG PFD in the hull and wear nothing.

The SI's can up the standard to WEAR a xxx....
This could be the zhik Flotation aid... (FD) This allows you to be state legal and comply with the RRS by putting a CG PFD in the hull and wear the zhik. (the type IV is a PIA)

The SI's can up the standard to the US Sailing... ie WEAR a PFD. That means that an aid is not legal.... you have to wear a CG vest and the orange PFD you can buy for the hull is useless. (Did I mention that the type iv throwable is a PIA)

The US Sailing uber standard of Wear a CG approved PFD is tossed around by OA's and half the time I doubt they know the distinctions.

Now that you have a headache.... good luck!....

Oh... BTW... the CULTURE is probably... they take you out back and beat the tar out of you for filing a protest on a PFD or a type 4 throwable against someone . So... don't do that.....

The dilemma is... you are breaking the RRS if you don't carry the throwable and stuff the bright orange pfd in your hull while wearing your zhik. This one is about your conscience. There are no ways around this foolishness.

Now... if you want to go to a US Sailing event... they have been known to check... and toss sailors midway through a regatta... usually these are junior events. One example made seems to scare the hell out of the fleet and lots of pfd's get sold that way. Usually they announce the pfd check for these regattas a head of time.

(and you thought that was a simple question.....)