Boating Bits

PRACTICAL BOATING: That sinking feeling

David Green relates a cautionary tale about ensuring water stays where it belongs: outside of your boat.

MOST boats will, if the circumstances are right, sink to the bottom. The following is a cautionary tale about what can happen when things go wrong and environmental influences change. Boats can sink two ways. The water either enters the boat from below, through a break in the integrity of the hull, or it sinks due to filling from above. One of the commonest reasons boats sink, particularly at moorings, is rainfall.
On the Gold Coast there are literally thousands of canal front properties and most of them have jetties.

In the recent torrential rainfalls in December 2007 a number of boats sunk at their moorings due to rainfall. While boats on trailers are relatively safe from this problem, it is important to go through the process of how a boat might sink in order to understand all the preventative maintenance required to avoid this disaster. The pictures nearby display the problems that arise when things go wrong, and you wake to find your pride and joy sunk at the jetty with just the front of the hull protruding from the water. It is the type of nightmare no boat owner wants to be a part of, but it can and does happen with amazing regularity!

Sinking causes

Boats sink from tiny pinholes if nothing is done to correct them. Breaks in the integrity of the hull can arise in any hull from corrosion, cracks along keels or welds and splits in internal pipes, kill tank drains or loose hose clamps. The risk increases greatly the longer the boat is in the water. Breaks in seals, perished washers around bungs or corrosion between screw fittings and aluminium hulls all lead to potential problems. Anglers who fish from trailer boats invariably take the bung out at the end of the day and generally soon know if there is a problem in hull integrity. If the boat is at a mooring the problem may be subtler, particularly with a slow leak. If you have a bilge pump with a float switch without an alarm, you may not realise the boat is leaking at all unless you notice the pump intermittently working.

If the boat is left at the mooring without facilities to constantly recharge the battery, then the bilge pump will eventually leave the battery flat, the pump won’t work and the leak will continue without being pumped out. One of the real problems with small leaks is that the more the boat fills up, the faster it leaks as the downward pressure increases the flow through the leak. By the same way that a broken porthole can sink an ocean liner, a pinhole can sink most boats. If your boat is moored then you need to be especially paranoid about the integrity of the hull and any leak at all needs investigating.

Leak spotting

Finding a leak can be tricky. In most bigger boats it is nearly impossible to look at the hull completely while it is in the water unless you have removable flooring. If the boat leaks at all it needs to be immediately slipped or put on a trailer. When you get the boat on a dry stand, leaks can be very frustrating things to find. In aluminium hulls common sites are around bungs and transom mounted screw fittings. Cheap plastic bungs are a constant problem, and most bungs on the market these days have washers that break or crack and screw threads that wear out. All of this leads to leaks. Cracks in aluminium hulls are generally close to the keel or on seams. Check your trailer very carefully, especially along skids and rollers and if you travel a lot on corrugated roads. Fibreglass boats can suffer from osmosis and the leak can swell and break internal timber, which may rot or distort leading to potential leaks.

There are a couple of handy tricks to finding a leak, which work most of the time. The first is to put a light source such as a cold fluoro lamp in the floor cavity of the boat and look for any light at night coming through the hull. The second is to mix some sodium fluorescein (once marketed as a fish attractant under the name of Glowbait, but also used by plumbers to find leaks in pipes) in a 1:1000 mix with water and fill up the boat with water as you are able, depending on your local water restrictions. The leak will have highly fluorescent green water coming through it if there is a leak. This picks up small leaks well. Water alone will pick up most leaks if they are big enough to drip. The take home message is never dismiss a wet bilge as insignificant without finding the cause.

Sink-proofing your boat against rain can be a bit more difficult if conditions are extreme. A bilge pump with a float switch only offers protection if it is connected to an inexhaustible power supply and if the pump-out rate is greater than the rate the hull could fill at. Open hulls are at much greater risk. As the nearby photos show, bow rider designs are at even greater risk as the water enters the hull from the entire length of the boat. Storm covers that drain water off the hull back into the water are essential items in areas of high rainfall. In heavy protracted rain a hull can rapidly sit very low in the water. On fixed moorings such as jetties this can make the up and down movement with the tide problematic, and if a hull full of water rolls and sits on the bottom at low tide it may get stuck under the mooring beams as the tide rises. If there is enough rain to sink the hull, so the transom height at which the engine sits is covered, the boat will sink in minutes as the engine will pull it under and the water will flood in very rapidly.

Rain can also enter a hull through leaks in covers, rod holders mounted in the transom and open or unsealed window fittings. If you are fitting out a covered hull to be moored, use those rod holders with protective rubber covers. A good bilge pump will only protect a moored boat while it has a power source. Battery charge must be maintained at all times. One battery is not enough if the boat is moored.

Traps & pitfalls

There are plenty of traps for new boat owners. While it is always appealing to moor a boat on a jetty for ease of use, it comes with inherent risk that many new boat owners just don’t appreciate. As the nearby pictures show, the sinking of the Sea Bunny leaves the owner with a monumental problem. A lot of pontoons are now fitted with trailer ramps or inflatable lifts. While this represents extra expense, it is a good way to prevent disasters and also stops the need for anti-fouling the hull as well.

Preventative maintenance is the key to avoiding such problems. Always check the bilge, make sure the float switch has an alarm or indicator when it is working, check your batteries and make sure you have plenty of them and a recharging system in place. Also constantly inspect your hull for leaks or damage, make sure the float switch is clean and not obstructed by debris. In times of heavy rain either remove your boat from the water or make sure you have storm covers so the hull doesn’t fill up. Heavy rain can rapidly add several thousand litres to your vessel, which may weigh several thousand kilos! This is a common reason that moored boats sink. Most modern marine engines are very difficult to get back to full function once sunk, and even if repaired are at great risk of ongoing corrosion and electrical problems. They are also difficult to sell for these very reasons.

Not many hulls possess enough flotation to avoid these problems and a lot of boat owners are blissfully unaware of how fast a boat can and will sink when things go wrong. Yesterday I was fishing offshore from the Gold Coast and a 2.4 million dollar catamaran sunk out on 36 fathoms when one of the intake pipes broke or loosened. This happened within minutes of the boat coming off the plane and commencing trolling. This unfortunate sinking happened in the middle of a game fishing tournament so there were plenty of boats in the vicinity, but in a more isolated area would have led to major rescue issues. The speed at which such a big vessel can sink is surprising.

Keeping a boat on a mooring requires vigilance bordering on paranoia. Storms and heavy rain mean everything needs to be checked over and over, and investing in a decent cover can save a boat from disaster in heavy rain. Plan your mooring very carefully and don’t learn from expensive mistakes!

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