Waves Can Sink Boats Even When It’s Calm

By Tom Neale, 8/4/2014


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We're all familiar with the perils of sinking. We all spend a lot of thought and effort to avoid it. Yet there's one type of sinking that few of us consider. It's a type and a cause, rolled into one catastrophic disastrous event. And many of us have been on its brink but didn't even know it.

Picture a good fishing day. You're trolling along the drop off, they're hitting and you're taking them in over the stern or quarter. The person at the helm has to play it just right, backing down to relieve line stress and to help getting that fish aboard. His goal is just that, before it breaks free. So often the helmsperson is backing down into the incoming seas. Most boats used for fishing are built to take this. The water comes over the outboard cutout or transom but quickly runs out again through the scuppers. But sometimes too much water comes over the stern to drain very quickly.

Bailing illustration

Picture a beautiful afternoon in a canoe. Weather's perfect, water's calm, two of you are paddling and you've got enough supplies for a fun day on the water... maybe even for camping. Your canoe is not quite as buoyant as usual because of the weight. A fast boat speeds by and throws a few waves over your gunn'le which is just a bit lower than usual because of the same reason. That weight isn't an overload. It isn't necessarily an unsafe amount, it's just a little weight. It's hardly enough to sink the canoe. Or is it?

Picture a fairly rough day. You're actually enjoying it because you and your boat can handle it and handle it well. Your boat is an express cruiser and, like so many, has a lot of open space below. This open space makes for comfort, cuts out claustrophobia at the marina and looks good when you take a guest below for the first time. You're running sort of slow because you should. It's rough and you've found the right speed to safely go over the waves without plowing the bow or sliding off into a trough. Let's imagine a scenario ... one that happens more than we'd like to think. As you're running along, the hose connecting your shaft log with the stuffing box tears. It quickly rips apart. Very likely the tear is because someone used exhaust hose in that application instead of stuffing box hose. Exhaust hose is too thin to withstand the torque constantly stressing it while running with the shaft turning at high speed inside it. It doesn't have the number of plies as does stuffing box hose. And it often has wire inserts which rust over time cutting into the hose and weakening it. When that hose tears you seldom know about it for awhile because it doesn't make a noise, cause a significant vibration or cause the engine to overheat. Eventually you'll probably notice it because the bilge pump doesn't stop running. But by then the water volume below may be huge and it's coming in fast through that tear which has opened the shaft hole which is now spouting huge volumes of water under high pressure.

What's one of the first things people do when they suddenly realize they've got a lot of water aboard? It depends, of course. In my old rowboats and outboard skiffs, the first thing I'd do was grab the bucket to start bailing. Of course, the bucket was seldom within reach and I'd have to move to the other side and/or the other end of the boat to get it. In a canoe you'd probably do essentially the same thing. And even in a canoe you'd probably have to move your butt a bit to reach it. In a center console fishing boat a common reaction is for some of the people to rush forward to keep from getting wet. Or some might grab the cooler to keep its contents safe. In almost any boat, if there's a sudden realization that there's a lot of water aboard, at least some of the people are going to start moving around fast. Whatever. ... the typical reaction is usually some sort of quick motion of the people aboard. It's a natural human reaction. And if that reaction doesn't occur, there's always the fact that it's a boat in the water, and even if it isn't a particularly rough day, the boat is prone to be rocked from side to side by wakes, small waves, or even gentle motion of the people within. Or, an improvident turn of the wheel could cause the boat to heel with a sudden shifting of weight to follow.

Tom's Tips
Tom's Tips About Sudden Flooding

1. In addition to appropriate calls for assistance and other safety steps, it's obviously important to try to find the source of the flooding, if you don't already know.

2. Often it's easy to temporarily stop even a big leak. This at least gives time for help to arrive ... or maybe for you to get to shore.

3. But quickly observe how movements about the boat affect the trim of the boat. Also observe the movement of any water you've taken on. Is it starting to move from side to side?

4. Depending on the type of boat, there could be enough water below, where you can't readily see it, to cause sudden imbalance.

5. Because of the possibility of even more flooding at a much faster rate, never put yourself in a position where you won't be able to quickly escape if needed.

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Some day when you've got nothing better to do, get a wash tub, fill it 1/4 or so with water, and tip it back and forth a few times. You'll see waves starting to wash from one side to the other. Very powerfully. And even if you stop tipping it, the waves will continue to roll inside that tub. As they do, they're drastically shifting a large amount of weight from one side to another. Water weighs approximately 8 pounds per gallon. Do the math in relation to that extra water in your boat. You won't know the number of gallons, but you'll know that it may not take much to substantially upset the balance of your boat. And those waves inside your boat will be much more effective than the ones inside the tub because the tub is round and the tub is sitting on firm ground. And that “effectiveness” could result in swamping, capsize, damage to important equipment or water coming in much more rapidly because open thru-hulls normally above the water line such as, for example, sink drains, are now below the surface.

A lot of us don't think about this. I've bought it up here because it's a very real and potentially very dangerous phenomenon. I first learned about it in my earliest days of boating, before I was a teenager. When my wooden rowboat sank while swelling up, or when I sank it to get the crab bait stink out, I'd raise it by standing alongside with a bucket, on a flat calm day, and reach over the gunn'les scooping out water faster than it came in. It was an almost losing battle, but usually I managed to raise those gunn'les a few inches or maybe even a foot above the surface of the river. Then it became much easier to bail from inside the boat, so I'd slither over the stern to finish the job. The first few times I sank that boat so fast that I hardly knew what was happening. Only after learning to slither over the stern very, very slowly and then plant myself firmly in the middle, with feet against each side so I could quickly do some stabilization when the load of water began to slosh, could I finish my job and be back in business.

As I think about how foolish I probably looked back in those days, it gives me a chuckle. But this is something that can be very serious for any of us when we get a lot of water inside the hull. We're going to move about in the boat, but the movement must be done carefully and deliberately with this issue in mind. We want to keep that boat on top of the waves...not the waves on top of the boat.

Boating and water sports involve risk. Any comments herein should be followed at your own risk. You assume all responsibility for risk or injury to yourself or others. Any person or entity that uses this information in any way, as a condition of that use, agrees to waive and does waive and also hold authors harmless from any and all claims which may arise from or be related to that use.

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