For me, the words damage control conjure claustrophobic scenes from the 1981 German U-boat film Das Boot. Begrimed men, stripped to the waist in rising water, struggling to plug gushing pipes that depth charges ruptured, all while the prying ocean tries to entomb them in their fragile biosphere. 

Admittedly, this article takes a rather less epic view of flooding because, thankfully, most of us only encounter the more humdrum elements of prevention and preparation. Serious hull breaches from grounding, collision or naval gunnery are special cases for another day. (But I do recommend the movie if you haven’t seen it.) 

Flooding is always a serious matter, but one reason it belongs in the pantheon of “things that went wrong that should not have surprised me” is that most boats are full of holes. Count ’em: propeller shaft, cooling water for the main engine, possibly for a generator, as well. Discharge regulations notwithstanding, a saltwater head functions on water coming and going through holes in the boat. How about a depth sounder? Another hole. A speed log needs a hole, and so does a mechanical bilge pump. Many boats have a saltwater hose for rinsing down. Where does that water come from? A hole. Some rudder arrangements involve a hull penetration near the waterline. Should your vessel be more extravagantly equipped, there may be intakes for refrigeration and a watermaker. Am I forgetting something? Probably, but you get the idea: Even on a good day, each of these holes represents a potential point of ingress. Just ask a marine insurance claims adjuster. 

Many holes are fitted with seacocks that can be closed in the event of a hose failure, so long as you can grab the handle before it submerges. This particular line of defense against flooding raises several points: 

1. Know the exact location and purpose of each seacock, and be sure there’s quick access to them. 

2. Maintain seacocks so that they are fully operational in time of need. 

3. Use at least two high-quality hose clamps at each end of a hose, and snug them up on a regular basis. (Actuaries really know about this one.) 

4. Replace hoses on a schedule, whether you think they need it or not. Hoses have a service life. They can deteriorate over time, with no outward sign of compromise. 

5. Consider closing seacocks when leaving the boat unattended. The only hazard here is that you remember to open them before starting machinery. 

For some of these measures to be effective, they must be logged. This level of meticulousness may be all too reminiscent of the very day jobs we seek to escape on a boat, but if you are old enough to own a boat, you are old enough to know that your memory isn’t what it used to be, if it ever was. If a task isn’t written down, you won’t remember it. 

Not all hull apertures can be fitted with seacocks. Examples include the prop shaft, transducers for sounders and speed logs. Since these are all well below the waterline, the incoming pressure can be considerable. What do you do if one of these lets go? I wish I had an easy answer. The only time I had a transducer fail, there was a Travelift handy to scoop the boat out of the water.

In the case of a transducer, it may be possible to hammer a damage-control plug into place (more on this later) and shore it in position. Wedging or cinching something malleable — a towel, blanket, pillow or rag, for example — into a hole or around a leaking prop shaft can slow the leak and buy time. A more technical approach is to construct a cofferdam over the hole. It’s essentially a box filled with hydraulic cement or something similar, which is then braced against the pressure. This isn’t an option for most boaters, but it gives an idea of what could be attempted with enough forethought. As always, deliberately grounding the vessel cannot be ruled out if there is a suitable place that won’t introduce significant new dangers to life and limb. 

If flooding cannot be stopped, all strategies point toward buying time for the pumps, which buys time for thinking and getting help. If your repair isn’t perfect, it may be good enough for pumps to keep up. This means having reliable pumps and some measure of redundancy. I have known too many cases where line after line of pumping defense failed because of complacency, with the skipper’s options turning out to be unavailable thanks to neglect. 

Even the best pumps cannot remove water if the water cannot get to the pump. Therefore, keeping limber holes clear and bilges free of clutter cannot be overemphasized. I recall a sack of laundry finding its way into the bilge, and each time the bilge pump engaged, the suction grabbed the sack, blocking the water. The person on deck monitoring the discharge saw the water stop flowing and assumed the bilge was dry while the boat was filling up. Another time, a roll of toilet paper wound up in the bilge, thanks to some brilliant stowage concept. The paper disintegrated, clogged the electric lift-switch pump and burned out the motor as the boat filled up. 

An assortment of wedges, tapered  damage-control plugs and pieces of 4-by-4, along with a mallet for seating, can provide options to control the ingress of water. Hose clamps, twine and other materials are equally versatile.

To control flooding, keep a few articles aboard that can facilitate your phone-booth-like transformation from citizen to superhero. A selection of tapered, soft-wood, damage-control plugs; a variety of wedges; pieces of 2-by-4 and/or 4-by-4 wood for bracing; a saw for trimming; and a mallet for whacking it all into place are standard kit for this sort of thing. Small pieces of plywood might prove useful, too. Tethering properly sized damage-control plugs at each through-hull fitting with a durable lanyard can save time in an emergency. 

Additional items to keep around include material for improvising gaskets, such as neoprene or rubber from an old tire tube; hose clamps; replacement hoses; tubes of goop; duct tape; twine; and an assortment of tools. Also, have critical spare parts for your pumps — diaphragms, impellers, gaskets. And buckets. Never underestimate a bucket. 

When your boat starts taking on water, time is of the essence. If you can stomach having yet another system installed, bilge alarms have a track record of doing exactly what they are intended to do, and they have been required on commercial vessels for decades. 

Last, there is a certain irony that a boat freshly launched after being overhauled at great expense can be most vulnerable to the kind of flooding just discussed. Anytime someone — however conscientious, however experienced — takes a thing apart and puts it back together, there is a chance it won’t go back together correctly. Propeller shafts, stuffing boxes, through-hull fittings and transducers are all candidates for this sort of human error. 

I have witnessed two serious prop-shaft leaks upon launching, one of which wasn’t evident until we were 100 miles offshore. The other occurred dockside but went undetected until 3 o’clock in the morning, by which time the mechanical bilge pump and main engine were submerged. A bucket brigade was the only functional response, and it worked. This, of course, was before bilge alarms were commonplace. 

No technique, piece of equipment or level of experience may suffice in a given flooding situation. But having a conversation with yourself about realistic countermeasures that are appropriate to your boat and to the way you operate it is well worth the time. 

This article originally appeared in the November 2017 issue of Soundings

This article was republished as “Know What to do When Your Boat Takes on Water” on July 12, 2021 of Power & Motoryacht Magazine.