Outewear for Yacht

Elite yachting or normal yachting?

Just spent a week on a fifty foot catamaran in the BVI.

Everyone wore polo's and t-shirts throughout. Anything nice would have been destroyed by fishing, saltwater or sloppy drinking.

PM Sir F. He will know.

Mostly sweatshirts, sailing jackets, etc.

Not sure what you're asking, but Musto is my choice for sailing outerwear.

Of course something casual, chinos, polos, shirts, sweaters, boat shoes, flip flops.

Will this boat be used for piracy?

Slightly off-topic perhaps but just as important.....
No matter how enjoyable boating or sailing can be, be prepared also for what could go wrong (injury, motion sickness, sinking, etc)
Make sure your jacket has reflective striping and a hood and many zippered or preferably velcroed pockets to keep your junk safe.
Wear a vented safari-type hat with a string to keep it on your head in a high wind. A pair of driving gloves kept in your jacket pockets can come in handy in bad weather. Check to make sure there are enough life jackets on board before commiting.
Sunscreen, bottled water, whistle, motion sickness tablets, portable first aid kit, flares and a good fitting pair of sunglasses are aslo a must. Who cares if they laugh? You are prepared. Stay hydrated.Post photos when you return!

Not yet.

Touché.

Get some thick wool sweaters and waterproof clothing too. Be prepared, it gets freaking cold on the water.

Also assuming you would be the one doing emergency repairs/engine work yourself. Bring some junk clothes for that, don't want to ruin nice clothes with engine grease.

Look to the classic.