PBO verdict

Most people are aware that even the best lock will only slow down a thief. You’re far more likely to inconvenience yourself if your lock seizes up – so there’s a balance to be struck between security and corrosion resistance.

The clear winner of the corrosion test was the Shield MC40 Chrome Marine Combination Padlock, which emerged after a month in our extremely corrosive tank completely unaffected. You pay for the corrosion resistance with a lowered resistance to attack, however, as stainless steel is less hard than more easily corroded metals – and it took only 10 seconds with a pair of bolt croppers to cut through the long shackle.

As we found on our last test, the best in terms of attack resistance is a discus lock and an effective hasp – and the Master Lock Combination Discus Padlock was by far the most resistant to attack. However, it didn’t appreciate the time in the corrosion tank, with the wheels completely corroded and jammed.

The Master Lock Pro Series Stainless Combination Padlock was a good compromise, with reasonable resistance to attack and corrosion, as was the ABUS 180IB/50.

Surprisingly good was the B&Q brass and steel lock, which despite corroding horribly still worked, and resisted a hacksaw for a minute.

Chromed brass and stainless steel seem best for coping with salt water, while a short shackle paired with a hasp which covers most of the shackle provide the best security solution. Whatever you buy though, the key lesson here is to keep your lock well lubricated if you want to avoid having to try to break into your own boat.