Originally Posted by Lodesman
Actually it means "your actions/intentions are unclear" or "I feel you're not taken sufficient action to avoid collision". Colloquially, it's known as the "wake-up!" signal, typically meaning "I'm standing on, waiting for you to manoeuvre - get on with it" or as is the case dealing with mafi/wafi types: "stop f-ing moving about, and let me avoid you."
There is another signal that says "you're standing into danger" - that's morse U (..-) - you might hear that near an oil
In the universe I inhabited when applied to small craft it meant 'get out of my way or die you dickhead!!!'
5 blasts is actually covered thus 'When vessels in sight of one another are approaching each other and from any cause either vessel fails to understand the intentions or actions of the other, or is in doubt whether sufficient action is being taken by the other to avoid collision
, the vessel in doubt shall immediately indicate such doubt by giving at least five short and rapid blasts on the whistle'.... and then you should be looking at doing something about it muy pronto.. not just blowing your hooter.....
The size of day shapes used to be covered by Annex I .... diameter of balls, cylinders and the base of cones was .6 metres, vertical distance between each shape was 1.5 metres..... ships of less than 20 metres could be of reduced size but 'commensurate with the size of the vessel'......