Can an Open Porthole Sink a Yacht? The Skipper's Checklist Before Leaving the Boat

When people imagine a yacht sinking, they picture a storm, a collision or a dramatic rescue. The reality is often much less exciting. A lot of boats go down because of one small mistake that nobody noticed, and one of the most common is an open porthole.

How one porthole lets the sea in

A porthole looks harmless when the boat is sitting flat in a calm marina. It's above the waterline, it's small, and the breeze feels nice in the cabin. The problem is that a boat rarely stays flat.

• Heeling. On a sailing yacht, the hull leans when the wind fills the sails. A porthole that was half a metre above the water can suddenly be below it.
• Waves and wakes. At anchor or under motor, every wave and every passing boat's wake splashes against the hull. An open porthole takes a little water each time.
• Weight shifts. Guests moving to one side, a full water tank or a dinghy on the davits can all change how the boat sits.

A single splash doesn't matter. Hundreds of splashes do. The water runs into the bilge, the bilge pump starts working, and as long as the pump keeps up, nobody notices. Once the water comes in faster than the pumps can get it out, the boat gets lower in the water, the porthole goes deeper, more water comes in, and things get serious very quickly.

Most sinkings aren't dramatic

Insurance data from BoatUS shows that many boats sink at the dock, not at sea. Their analysis of small outboard boats found that sinkings at the dock happened about four times as often as sinkings under way.

The causes are boring: rain filling a cockpit when the drains are blocked, a leaking hose or fitting below the waterline, something left open, or a bilge pump with a flat battery. The common factor is that nobody is on board to notice.

That's the scary part. A boat can sink in a calm marina on a quiet night, tied up and completely safe, because of a mistake someone made hours earlier.

Portholes, hatches and seacocks

Every boat has three kinds of openings worth thinking about:

• Portholes are opening windows in the hull or cabin sides. They sit lowest, closest to the water, so an open one is usually the biggest risk.
• Hatches are openings in the deck. They're higher up, but in heavy rain or green water over the bow they can still let a lot in.
• Seacocks are valves on the holes below the waterline that feed the engine, toilets and air conditioning. If a hose behind one fails while it's open, water pours straight in.

My checklist before leaving the boat

This is what I go through every time, whether I'm leaving for an hour or for a week:

1. Close and lock every porthole. Not just pushed shut: locked, with the handles fully tightened.
2. Close every hatch. Including the small ones over the heads and the anchor locker.
3. Close the seacocks you don't need. Toilets and sinks especially. Leave the ones that must stay open, like cockpit drains.
4. Check the bilge. It should be dry or close to it. Water where there shouldn't be any is a warning sign.
5. Test the bilge pump. Make sure it switches on, and that the batteries will keep it running while you're away.
6. Clear the cockpit drains. Leaves, rope ends and plastic can block them, and then one heavy rain fills the cockpit.
7. Check the mooring lines. In a stern-to marina, lines that are too tight can pull the stern down when the water level or wind changes.

It takes two minutes. Compared with the alternative, it's the best two minutes you'll spend on board.

Captain's note

The sea doesn't need a storm to take a boat. Sometimes it just needs one porthole someone forgot to close. Make the checklist a habit, and you'll never have to make that radio call.

See you on the water,
Captain Phil

Source: Soundings, on BoatUS research into the causes of sinkings.