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Travelling in Shallow Water

Travelling in Shallow Water

We are blessed with an abundance of beautiful waterways across the Gold Coast and Moreton Bay, but they are also home to some of Australia’s shallowest water. Tearing through these waters without paying enough attention can easily get you grounded, stuck, or worse. HAYDEN WYLD from Wyld About Boats, has been boating for 35 years and gives us some essential tips to help you brave the Coast’s shallow waters with confidence.

 

AREAS TO WATCH OUT FOR

Particularly shallow areas to be careful around are at the southern end of the Broadwater. Straying outside of the channels here will put you on the sand in the blink of an eye. More than a few boats have run aground on the sand bar just south of the Couran oyster leases too (the area known as The Aldershots). It is also important to take extra care around oyster leases because the structures in the sand will do some serious damage to your boat.

Several parts of Moreton Bay and North Straddie are also dangerously shallow, especially the crossings on the north side around Amity Point, and at Jumpinpin on the south side. The council do their best to dredge these areas, but they cannot keep up with the huge volumes of shifting sands. To be safe it is always best to use the Seaway instead.

RESEARCH BEFORE GOING OUT

Asking local boaties for advice on safe spots and places to avoid is helpful. Check the boat ramps in your area. Some of the new ramps have been designed to give you easy access to deep water, particularly the new one at Southport.

Make sure you check the tides before heading out, especially when you are going to the Seaway. You do not want to go out on a runout tide because the channels are always more exposed at low tide. Although it is much safer on the high tide, it is still possible to end up on a sand bar.

TECHNOLOGY TIPS

The key to avoiding shallow water is knowing exactly where the deep channels are. If you do not have the advantage of years of local experience, the best way to keep yourself safe is using a GPS device that displays detailed maps and depth information, and to have a physical Beacon-to-Beacon handbook that shows all the channels. With both of these, you can make sure you are always sticking to safe water.

While it is true that sounding equipment can give you accurate real-time depth readings, it is important not to rely solely on them because most of the time you will have already run into trouble before the soundings alert you. Not even side-scanning transducers can guarantee safety at speed.

SHALLOW SAFETY

Travelling at speed when you are out of the channels multiplies the dangers, so keep your boat to a sensible six knots. The worst thing is if you hit a sand bar at speed, because the boat stops suddenly and sends you and your crew into the windscreen. Most boats are strong enough to withstand hitting a sandbar, but you may not be so lucky.

If you do hit sand, the first thing to do is turn the engine off and carefully assess the situation. If you are badly stuck, or if you have suffered injuries or damage to the boat, then the best thing to do is to call the Coast Guard or VMR to help you out. Do not take chances.

If you are only lightly touching the sand, then you might be able to try just trimming your engines so they are clear of the bottom and slowly pulling away. Do not try to aggressively power out because all you will do is churn up the sand and damage your engine. If going slow with the engines trimmed still is not making progress, then you should try getting any extra crew you have out of the boat to help push and rock it while you gently apply power.

Whatever you do, make sure there is water flow getting through the engine to keep it cool. Keep an eye on the gauges to be sure. Also, you want to avoid sucking up any sand, and you will have to check the seawater filters and clean out any blockages.

If your boat is a shaft drive, then you will want to be especially careful in shallow water because they tend to suffer more damage when they run aground. It can also be very difficult to inspect the damage because you will either need divers or to lift it out of the water.

Taking the extra time to cruise carefully through the shallows will avoid those hefty repair bills if something goes wrong

 

By Narayan Pattison

 

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SHALLOW WATER EFFECT

By Nic Welch

There is a hydrodynamic phenomenon known as the “Shallow Water Effect”, otherwise known as “Squat Effect”, where a vessel’s draft actually increases when travelling at speed across shallow water.

This is caused by the water being squeezed between the bottom of the hull and the seabed, causing the flow of water under the hull to move faster than it would normally do in deep water. This faster flowing water in turn causes the vessel to be sucked towards the seabed, increasing the vessel’s draft.

Side effects of the “shallow water effect” include:

• Reduction in vessel speed

• Increase in vessel draft

• Sluggish steering

• Change of trim causing the vessel to dip towards the stern or bow

The side effects of the “shallow water effect” can be avoided by a reduction in vessel speed.

In 1992, the cruise liner Queen Elizabeth 2 with a draft of 9.8m and travelling at 24 knots, struck a rock at a depth of 10.5m. Investigators believe the “shallow water effect” was a contributing factor, with estimations of an increase of draft, at that speed and depth, was between 1.4m and 2.4m.

 

 

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