How to tell how far you are offshore on a jet ski

In the main, most jet ski riders are good, responsible people. But like everything in life, there are a few bad apples who ruin things for everyone else.

New rules introduced to Port Phillip Bay in Victoria late in 2019 join a growing movement throughout Australia to crack down on irresponsible riding by ensuring that jet ski operators are well clear of swimmers before they start to have fun.

The Victorian laws are very similar to those rolled out in NSW; jet ski operators must travel in a straight line and at low speed for a set distance to and from the shoreline.

The question is, how does a jet ski operator, who more than likely doesn’t have a speedometer fitted to the personal watercraft, know when they’re in the clear?

It’s a simple case of counting.

Speed is calculated by dividing distance by time. We already know that jet skis have to slow to 5.0 knots – about 9km/h, or a slow jog – when under enforceable speed limits, so it’s a matter of some simple maths to travel a safe distance offshore.

v=d/t

To travel 50 metres offshore, we divide our distance, 50 metres, by the speed, 2.5 metres per second, to get a time of 20 seconds.

Therefore, we need to drive in a straight line at the same speed as a slow jog for at least a slow count to 20 before we can start having fun.

Remembering this multiple will help you in special zones where a jet ski needs to travel in a straight line for at least 200 metres before it is safe – and legal – to start having fun. Multiplying our 20-second count for 50 metres by four gives us 80, the new number we need to count to so that we cover 200 metres.

In some parts of Victoria’s Port Phillip Bay, jet ski riders will need to be a total of 500 metres – that’s half a kilometre – offshore. Keep counting to 200 before you start to have fun.

The hard bit, of course, is where to safely slow down on the way back into shore. After you’ve finished counting, it pays to stop and look back to shore to try and get a measure on how far out you need to be.

This is where you use an old fishing trick to help you, lining up onshore landmarks to triangulate your position on the water. Another easy way is to use a finger held at arm’s length to measure the height of something onshore – a tree or a building – that’s a finger’s width tall, and use that to determine that you’re back in the slow zone.

Use these tricks and you’ll never get in trouble from the authorities about where you start to have fun.