Hidden hazards

Mark Robinson | VOLUME 22, ISSUE 1
The very unpleasant grinding of metal on rock is heard and your craft shudders to a halt.
We take a look at one of our most common claims issues – hitting submerged objects…

It is said there are only three kinds of skippers; those who have run aground, those who will run aground and those who have, but won’t admit it. Unfortunately, that oft-quoted tongue-in-cheek statement is all too true. Insurance statistics verify that a significant number of claims are generated by hitting submerged objects of one kind or another. Let’s look at a few examples, imagining in each case that you are the skipper. After reading each example, pause and consider what really caused the accident and how it could have been avoided.

Scene One: You’ve anchored your 6-metre cruiser close inshore in a scenic bay you’ve visited a few times before. You’ve enjoyed a nice lunch and a glass of chilled white wine, but now the wind has swung around and the motion at anchor has become uncomfortable. You decide to move to a bay that you’d checked out earlier that day and so you up-anchor and head off. Although the water appears fairly shallow, you know from your morning’s exploration that it is deep enough to clear your propeller by a small margin – until the very unpleasant grinding of metal on rock is heard and your craft shudders to a halt on a small underwater outcrop, known by the locals as ‘the Pinnacle’.

Scene Two: You’ve had a lazy day on the water with some friends, caught a few fish, had a few laughs and now you are approaching the boat ramp where you launched early that morning. As you swing in towards the ramp to put a crewman ashore to bring down your rig, you become aware that there’s a strong wind blowing and it’s on your beam. Your thoughts are now preoccupied with how you’re going to drive your craft straight up onto the trailer. The ramp is crowded so you spend some time circling and waiting for the slow pokes to clear some space, but then spy a spot that has just become vacant. To avoid one of the other boats grabbing it, you quickly hit the throttle and as you do your prop hits something hard and makes, what you know from experience, expensive noises.

Scene Three: Your long-awaited summer holidays have begun and you and your family have set up camp by a lake you’ve always wanted to visit. The next morning dawns and you launch your ski boat just on sunrise. Your teen age son perform safaultless beach start as you roar out onto the lake’s mirror smooth surface. He’s yelling with excitement as he cuts back and forth across the wash and your wife is acting as observer while your pre-teen daughter on the rear lounge is somewhere in iPod Land. It’s time to make a turn so you make the appropriate signal and then swing in toward the lake shore, enjoying theg-forces as the craftheels. Then, without warning, there’s a thump and bump as the boat stops almost in its own length. You’ve run aground, hurling your daughter violently forward, where shen arrowly misses hitting her head on the dash. Meantime, you’re also thrown forward, your chest smashing into the steering wheel and head pounding into the sharp metal wind screenrim. There’s blood on the gelcoat, your wife is screaming in shock and your son is left treading water and wondering what went wrong.

Three scenarios with a common denominator; hitting submerged objects. Each case could have been caused by a number of factors so let’s consider them, one scene at a time. How did you fare with Scene One? Let’s take a closer look at what happened…

In Scene One, you might have been navigating visually and, as shorelines appear somewhat different from various angles – often influenced by the angle of the sun – you erred in your track and cut in too close to shore. Perhaps you did so because, earlier in the day, the sun was overhead and bottom contours could be seen quite clearly. But on the return leg, the sun was behind the high cliffs ringing the shoreline and throwing a large shadow onto the water, making the bottom much more difficult to see. And did you allow for the change in tide? Did you check the tide tables for the area and factor them in for the time of day? Had you looked at a chart of the region to familiarise yourself with the bottom contours, depths and any local hazards? And speaking of charts, do you know how to read one? Do you know, for example, what the chart datum refers to where it lists depths? Do you know the draft of your vessel? Do you travel with your depth sounder on and the shallow alarm set? Somewhere among these questions is the cause of the accident.

In Scene Two, you might have been preoccupied by the strong cross wind and not noticed just how low the tide was at the ramp. The situation may be been compounded by the strong offshore wind combining with a spring tide, which, if you’re not aware, has nothing to do with the seasons of the year. Roughly twice a month, the moon is in line with the sun and their combined gravitational pull creates bigger tidal movements called spring tides. Spring tides have higher high tides and lower low tides. Unfortunately, your arrival at the ramp just happened to coincide with the bottom end of a spring tide. Then again, maybe you hit because of the sudden throttle movement? This, of course, will cause the bow to suddenly rise and the stern to dip. If you don’t have enough water under you, you’re going to strike bottom. This movement is accentuated if the outboard, or leg is tilted, which is often the case when approaching a boat ramp or preparing to retrieve the boat. Maybe it’s the ‘familiarity factor’ that is often referred to in motor accidents? Statistics demonstrate that a significant number of road accidents occur quite close to where a person lives. The theory is that the driver lets down his or her guard when in a familiar location and this same factor may have caused you not to exercise as much caution as you normally would. Certainly, marine insurance statistics reveal that a high percentage of craft striking submerged objects do so close to the launch ramp or berth. Other factors which can account for this incidence include poor signage adjacent to ramps or in channels and perhaps poor availability of charts.

In Scene Three, there are a number of factors which could have brought about the accident, the first of which may have been unfamiliarity with the lake. Before roaring around at speed on an unfamiliar piece of water, you should have performed an initial exploration, using a depth sounder if you have one. Alternatively, you could have done a visual check, motoring slowly around with family members, looking over each side for obstacles or shallow areas and making sure you restricted yourself to the area you surveyed. You should also make an effort to find out from locals and other lake users what hazards there are and what areas you need to avoid. Caution on inland waterways is becoming critically important due to the current drought. Many rivers, lakes and dams now have lower-than-usual water levels, so tree stumps and other hazards may be lurking much nearer the surface.

Summary: In reviewing the various reasons why the above incidents might have occurred, we can draw up a list of preventative measures.


Just being on the water has the potential for danger at any time so from the moment you launch from your trailer or slip your mooring, you must remain vigilant at all times. Vigilance means scanning the sea around you through all 360 degrees, keeping a sharp lookout for bathers, fishermen, swimmers, canoeists, debris and any tell-tale signs of underwater hazards. Polaroid sunglasses are a must-have item because they reduce water surface glare and enable better visual penetration through the water. Decent Polaroid sunglasses allow you to see much more underwater detail, giving you a better chance of seeing and avoiding submerged hazards.


We live in an electronic age in which there can be an over-reliance on gadgets such as chart plotters and GPS units. They are, of course, valuable tools on any boat, but electronics, like any machinery, can fail. Therefore, you should buy a stock of official paper charts of the areas in which you intend to navigate, including your local area. Learn to read charts and study them. Memorise the geography of the land and the topography of the water. Hazards change with time and such things as temporary lights, dredges and other transient hazards to shipping need to be updated on your charts. Fortunately, this process has been vastly simplified since the Australian Hydrographic Service introduced a system that allows mariners to receive Notices to Mariners for their charts by e-mail. This free service is called eNotices. Subscribers must register to use the service via the web-site. Users create their portfolio of charts, allowing e-mail notices to be automatically generated when Australian Notices to Mariners are released, based on each individual chart portfolio. The site to register with is: http://www.hydro.gov.au/n2m/about-notices.htm#enotices.Depth sounders

Depth sounders have been popular for many years, especially in sea-going craft. They are a very versatile instrument that can be used on lakes, rivers and bays, as well as offshore. These devices calculate depth by measuring the round-trip time for a pulse of ultrasonic energy broadcast from the boat to the bottom and back. When left on while underway, depth sounders provide a continuous picture of the depth under your boat and can alert you via a depth alarm if you are entering shallow waters. However, some models do not work very well at speed and you should also be aware that, when travelling at speed, the depth alarm needs to be set with a safety margin in mind, allowing you to bring the vessel to a halt before you hit bottom.

Moving water

Different sections of our wonderful Australian coastline present different hazards, such as strong currents and tidal streams. In coastal areas, tides are accompanied by changing horizontal movements of water called tidal streams. Although there is interaction between the two phenomena, tidal streams are distinct from ocean currents. Tidal rips, overfalls, and the speed and direction of tidal streams and offshore currents are all indicated on charts and you should take them all into account when you’re planning your course.

Tidal effects

The difference in the height between a consecutive high water and low water is called the ‘range of tide’ and this varies around our coastline, sometimes to quite a marked degree. For example, in the Kimberleys, it can be as much as 12 metres, while around Sydney and Fremantle it is much less, usually in the region of 0.7 metres. Naturally, therefore, you should always be aware of the tidal movements in the area in which you are boating. Tidal information for any part of Australia is readily accessed on line at: http://www.bom.gov.au/oceanography/tides.

Weather and tides

Weather conditions affect tides in various ways, as do wind direction and strength. A high atmospheric pressure prevents a tide from rising to its full forecast extent, while a low pressure allows it to rise higher than normal. A strong onshore wind will push more water toward the shore, causing a higher tide than predicted, whereas an offshore wind will result in a lower tide, with a consequent increase in risk when boating close to shore. In certain weather conditions, such as a spring low tide combined with an offshore wind, a track that you may have previously taken across a bay may become more hazardous than usual and you might hit bottom. Or, while your experience has shown that you are able to safely clear a local bar with a minimum 0.6-metre tide in normal conditions, wind strength and direction might result in a depth of just 0.4 metres – just enough difference to have you hit bottom and grind to a halt.

Local knowledge

Nothing substitutes for local knowledge. If you are going to launch in an area which is unfamiliar to you, it pays to ask about any tricks and traps the local waters may hold. This is particularly critical if you intend being on the water at night, or during times of reduced visibility. Tackle shops are a good source of this kind of information; after all, they want you back as a repeat customer. Local marine rescue groups are another excellent resource as are police stations in country areas where the local constabulary would much prefer to offer preventative advice than to have to mount a rescue effort.

Know your craft

Knowing your craft includes knowing its particular quirks in handling, but in terms of avoiding hitting a submerged object, it particularly refers to knowing your draught. With a planing vessel, the draft is much less when planing at speed than when running at displacement speed or only half on plane; in other words, almost – but not quite – over the planing ‘hump’. The relevance of this is that in rough conditions, you may have to travel at this awkward speed and should therefore be aware that you may be drawing more water than you thought. If you’re in shallow water, you’re much more vulnerable to grounding.

Ultimately, as a skipper, you are duty-bound to do all you can to ensure the safety of your passengers, yourself, those in the water around you and your boat. Collisions with submerged objects account for a large percentage of Club Marine’s insurance claims. Boats are damaged and sometimes people are injured or killed. All of these claims are avoidable. It’s about doing all you can to minimise risk. By developing the habits of a good skipper, as outlined, your chances of running aground or hitting a submerged object will be substantially reduced.

Case Study

What lies beneath

Rottnest Island, in WA, is a prime example of one of Australia’s most notorious areas for groundings…

Despite detailed navigation charts and sophisticated technology, WA’s Rottnest Island is surrounded by some of Australia’s most treacherous waters and, according to rescue authorities, has the nation’s highest number of boating incidents involving under water damage to hulls, motors, shafts and propellers.

In fact, the aquatic playground located 18 kilometres off the coast of Fremantle has no less than 14 historic shipwrecks dotted around its coastline, some dating back to the seventeenth century. Today, a large number of sailors, many with years of experience, still fall foul of its hidden reefs, tides and currents.

The island’s beautiful bays, with crystal clear waters and white sandy beaches, are protected by a unique coral reef with narrow openings to the Indian Ocean. This is where most vessels come to grief. Once inside the bays, a sharp watch is required for underwater rocks and, ironically, the most dangerous time is when the weather is fine and the seas are calm.

“You don’t have to be inexperienced to come to grief. On a calm day, you can’t see the breakers over the shallow water,” says Frank Pisani, operations officer of the Fremantle Volunteer Sea Rescue Group (FVSRG), which services the water between Fremantle and Rottnest Island.

Three years ago, Frank was onboard the group’s main rescue vessel, the since-replaced R100, in calm weather about 400 metres offshore when it was hit by a seven- to 10-metre wave and dumped onto a reef. Fortunately, Pisani was inside the cabin when the vessel rolled and was able to climb out of a window as water started flooding in.

The wave that hit the FVSRG boat apparently came from a storm system hundreds of kilometres away and went unnoticed until it hit the shallow waters around Rottnest.

“Even with the experience that we have, you can get caught out. People don’t realise the waters around the island are absolutely littered with rocks and reef,” says Pisani.

Another incident involved a $500,000 Bertram cruiser. The owner was a very experienced skipper, but he got caught with the sun in his eyes and ended up hitting a reef.

In the 12 months leading up to October 2006, the FVSRG was called out to 55 incidents in and around Rottnest. Fifteen of those were of a distress nature, with the majority of calls attending to vessels aground on reef.

The Rottnest Island Authority (RIA) stipulates all large cruisers should be adequately covered by insurance in cases of salvage or pollution caused by vessels running aground. Previously, the RIA was left to foot the salvage bill if the owner of a wrecked boat was not insured. It’s now compulsory for owners of large pleasure craft visiting Rottnest to hold $1million third party insurance cover.

The Boating Industry Association of Western Australia conducts several Rottnest Island Safety Convoys during the year to help boaters become familiar with the ocean crossing from Fremantle, as well as navigating its many coves and bays.

For more information, contact the BIAWA on: (08) 9271 9688 or visit: www.biawa.asn.au.

– Barry Wiseman

How to-Safety