Some readers will be sufficiently senior to remember when wreck buoys were green. Believe it or not, that’s two changes ago. Permanent wrecks that pose a danger to shipping are now marked with a set of cardinal buoys, but when a vessel goes down in a hurry a new temporary wreck buoy system is put into action. Buoys are blue and yellow with a cross topmark. They flash alternate blue and yellow as well. They are usually laid around the periphery of a wreck. Although you won’t see them every day, it’s worth giving them a wide berth when you do.