I’ve always enjoyed walking the towpaths of England’s canals and for the past couple of years I’ve enjoyed boating on them too. This has led to an interest in the workings of these watery ways and recently I’ve discovered the secret of the blocking pin.
A blocking pin is part of a clever arrangement that was used to help a horse pull a narrowboat out of a lock and be on its way up the canal with minimum delay. It took a considerable effort to get these heavy boats moving from a standstill so the boatmen were provided with this cunning device to give the horse a helping hand.
The blocking pin is a curved iron spike that looks like a hippo’s tooth stuck in the towpath just after the top gates of a lock and pointing away from the lock. The boatman would drop the loop in the end of his tow rope over this ‘pin’, take it back through a rigging block attached to the bow of the narrowboat and then forward again to the horse. This gave a 2:1 purchase, enabling the animal to get the boat moving with half the effort – like changing down a gear. This arrangement had the added advantage of keeping the boat in the centre of the lock, away from the stone lock sides, further easing the burden on the horse.
Now the clever bit: As the boat moved past the curved pin the loop in the tow rope would slide off the pin and run back to the block where it would it would be stopped. Towing would continue seamlessly but at a 1:1 gear ratio. The equivalent of switching up a gear, automatically!
This may be old hat to canal boaters but for a salty sailor like me it was a revelation. (Thanks to Brian McGuigan for the use of his photo)