All vessels must have a sound signalling device such as a horn or a whistle.

Sound signals are often used by large vessels to indicate their manoeuvring intentions.

For example, the Manly ferry when about to reverse out of Circular Quay will communicate this to other vessels with three short blasts of their horn to raise awareness to other vessels in the vicinity.

Reverse, three short blasts. 

Marine radios are a great way to get assistance when you're more than 2 nautical miles form the shore.

Mayday - the whole vessel is in grave and immediate danger

Pan Pan - an urgent signal to indicate that you require assistance but there is no immediate danger.

For example, you've run out of fuel and will hit the rocks in many hours time. you need fuel urgently but you'll live. This would be 'pan pan'.

However if you've run out of fuel close to the dangerous rocks and will impact them in a few minutes, you would use a 'mayday' call.

Securite - a safety signal to indicate an issue such as log in the river or a weather warning

Floods rise the water level, meaning a clearance of 10m under a bridge, may quickly become only 7m.

With this question, the key is to take time to read it in full before answering.

Marine radios must be carried onboard when boating more than 2 nautical miles from the shore.

They are used to signal for emergency assistance, get important weather updates and more.

We've also made a helpful study video about this.

Speed is a major cause of boating accidents.

Take early and substantial action to keep well clear

Submarine cables are underwater cables used for telecommunications, such as phone and internet lines.

They will be marked by a Submarine Cable sign, which will indicate that you must anchor at least 200m away.

We've also made a helpful study video about this.