A boat takes on water faster than you think and a bilge pump moves it slower than you hope. That gap is the whole problem, and most cruising boats I see in French marinas are kitted to lose the race. People fit one electric pump, tick the box, and assume the bilge is sorted. It is not, and the maths is brutal once you look at it.
Why one pump never wins
Start with a number that should worry you. A hole the size of a 40mm seacock, a foot below the waterline, lets in roughly 250 litres a minute. A typical electric bilge pump advertised at 2,000 GPH (gallons per hour) sounds enormous until you convert it: that is about 126 litres a minute on paper, and once you account for head height, hose friction and a half-charged battery, the real-world output is often half the sticker figure. So your single 2,000 GPH pump is bailing maybe 60 to 70 litres a minute against an inflow of 250. You are going down, just slowly enough to feel hopeful.
This is not scaremongering. It is why every serious heavy-weather authority treats dewatering as a layered system rather than a single device. You want multiple ways to move water, powered and human, and you want them sized for trouble, not for the slow seep of stuffing-box drips. The same sober planning applies as for any committing leg, which the biscay passage planning write-up sets out for the Atlantic crossing where help is hours away.
The layered kit I carry
Here is the actual dewatering chain aboard our boat, in order of how I would reach for it.
A high-capacity electric pump on a float switch handles the routine: rain, drips, the bit of sea that always finds its way below. Wire it on its own circuit, not through the domestic fuse board, and mount the float switch where it cannot jam on a stray sock.
A second, larger electric pump mounted higher up acts as the emergency unit, with its own switch and ideally its own battery feed. The logic is simple: if the bilge is rising past the first pump, you want a bigger one cutting in, not a single point of failure.
A manual diaphragm pump that you can work from the cockpit is the one that keeps going when the batteries are flat or the engine is underwater. The Whale Gusher line is the reference here. A Gusher 10 shifts around 65 litres a minute at a hard pumping rate; the bigger Gusher 30 manages up to about 117 litres a minute at 70 strokes. Those are real hand-powered figures, and a fit crew member on a Gusher 30 outpumps a tired electric pump on a dying battery. Fit the through-deck or bulkhead version so you can pump without leaving the safety of the cockpit.
The last line is the engine itself. A simple change-over valve on the raw water intake lets you draw the engine's cooling pump from the bilge instead of the sea, turning your diesel into an emergency dewatering pump. It is not huge, but it runs as long as the engine does and costs almost nothing to plumb in.
The bucket nobody mentions
The most effective emergency bailer ever tested is a frightened person with a bucket. A 10-litre bucket emptied every five seconds moves 120 litres a minute, which beats most electric pumps and never runs out of battery. Carry two stout buckets with lanyards, not the brittle supermarket kind. They double as deck-wash buckets the other 99 percent of the time, so they cost you nothing to keep aboard.
This sounds primitive next to a slick electric pump, and that is exactly why it gets forgotten. When the water is over the floorboards and the lights have gone, the bucket is the thing that works. Keep it where you can grab it in the dark.
Plugging the hole comes first
No pump out-bails an open hole, so the dewatering kit starts with stopping the inflow. A set of soft wooden bungs, tapered and tied to each through-hull, is the oldest trick for a reason: hammer one into a failed seacock and you have turned a gushing leak back into a manageable drip. A self-amalgamating tape, some thickened epoxy putty and a couple of the modern self-expanding emergency plugs round out the kit. A collision mat or even a sail dragged over the outside of the hull buys time on a bigger breach.
Knowing where every seacock is, and being able to reach it fast, matters more than any gadget. Walk the boat and check you can put a hand on each one in the dark, because the leak never happens in daylight on a flat sea. If you are short on hands while one person plugs and another pumps, the deck setup in the short handed deck gear piece is worth reading, because dewatering a flooding boat with two people is a brutal division of labour.
French waters specifics
The flooding scenarios on the French coast are not exotic. A grounding on a falling Brittany tide can open a seam as the boat takes the ground awkwardly; a fishing-pot line round the prop can be dealt with calmly until you realise the stern gland has been disturbed. The point is that the dewatering kit pairs with calling for help early, and in France that means the CROSS station on VHF, who task the SNSM lifeboats.
If it gets beyond the pumps, the plan steps up to the liferaft, and the two decisions go together. The choosing liferaft french coastal piece covers the stage where you stop fighting the water and start preparing to leave, and the epirb or plb cruising france beacon is what tells the rescue services exactly where you are while you do it.
Test it before you need it
A dewatering plan that has never been run is a hope, not a plan. Once a season we pour a few buckets of water into the bilge and run the whole chain: float switch trips the first pump, manual switch fires the second, someone pumps the Gusher from the cockpit, and we time how long it takes to clear. The first time we did this we found the emergency pump's float switch had jammed with grit and the manual pump's outlet hose had perished. Both would have failed silently in a real flood.
Check the obvious things while you are at it. Are the bilge pump strainers clear of the debris that always collects in a working boat? Is the manual pump diaphragm still supple, or has it gone hard with age? Can you reach the change-over valve on the engine intake without dismantling half the cabin sole? Do the wooden bungs still fit their seacocks, or have they swelled and cracked in the damp? A dewatering kit decays quietly between emergencies, and the only way to trust it is to exercise it.
Brief the crew too. In a flood the skipper may be the one with a hand jammed against a failed fitting, so everyone aboard should know where the buckets, bungs and manual pump live and how to call the CROSS station on VHF. A plan in one person's head is not a plan.
A quick reckoning
Cost the whole dewatering chain and it is modest against the value of the boat. A serviceable second electric pump, a Whale Gusher manual, a change-over valve, a bag of bungs and two good buckets comes in well under a few hundred euros. Compare that with the single 2,000 GPH pump most boats rely on, and the upgrade is one of the cheapest pieces of real safety you can buy.
Water aboard is a time problem, not a panic problem. Lay the kit so that every layer buys you minutes, and minutes are what get the lifeboat alongside before the floorboards float.
