Koopvaarders Lock in Den Helder, Netherlands connects the Noordhollandsch Kanaal to the Nieuwediep.

After the Netherlands became independent again in 1813, King William I took a closer look into the commercial possibilities at Nieuwediep.

It was called Koopvaardij Schut en Waaijersluis (Commercial Lock with fan gates), but also Koopvaarders Schutsluis.

Koopvaarders Lock II was built in connection with the construction of the Noordhollandsch Kanaal.

As such, it was constructed as close as possible to the entrance of the canal, i.e. just west of the Nieuwe Werk.

However, each time it retained its name Koopvaarders Lock and function, i.e. to service commercial ships using the Noordhollandsch Kanaal.

The city council started by noting that the Navy Lock which had been built at Nieuwediep, was unsuitable for sea-going ships.

It was only 33 Amsterdam feet (0.2831 m) wide, that is 9.34 m. That made it suitable for small vessels, but not for the frigates and brigs used at open sea.

To this beam 1.5–2 feet had to he added on each side for the external fixtures of the rigging, and so the Navy Lock was too narrow.

As regards draft it stated that a lock would require a depth of 15 Amsterdam feet on the gates, or 4.25 m below inland summer level.

In the new plans all types of warships which were constructed at Rijkswerf Amsterdam had to be able to use the Noordhollandsch Kanaal to get to the navy base at Willemsoord.

This requirement fixed the width of the new canal locks at somewhat above 15 m, so all warships except the first class ships of the line could use them.

From the northern side the frigate Christina Bernardina from the East Indies opened the canal.

From the southern side, the canal was opened by frigate HNLMS Bellona, but it's not known when she entered the Nieuwediep.

In July 1825 there was mention of constructing facilities on the canal near 'the newly built double lock on the Nieuwediep, near the Nieuwe Werk of 1792'.

On 19 October 1825 the maintenance of the Koopvaarders Schutsluis was tendered,[6] implying that it had quite recently been completed.

On 3 June 1858 the order to construct a dam on the sea side of Koopvaarders Lock II was tendered.

[9] After Koopvaarders Lock II became operational in about 1825, commercial ships continued to increase in size.

Shipping to Amsterdam depended on Koopvaarders Lock II, and so it could not be decommissioned for lengthy repairs.

Therefore, Koopvaarders Lock III was built slightly to the south, and a small bit of Fort Oostoever was chipped off.

On the 13th a clean up was started, and the rest of the pile driving was expected to take place quickly.

[16] Just how important pile driving was with regard to the lock is shown by a state of day wages paid to several categories of laborers.

The company then repurposed it to a location where it could effectively renew the paint layer of ships, while doing this in an environmentally safe manner.

[27] In November 1981 the government recognized the urgency of building a new lock, but stated that financial problems prevented execution of the plans.

Now, the authorities decided to change Boerenverdriet Flood Gate to a regular lock, in order to lessen salt water infiltration.

However, after the renovation Boerenverdriet will be used by recreational vessels, and Koopvaarders Lock IV only for commercial shipping.

The name Koopvaarders Sluis has been explained by stating that only merchantmen used this lock, and navy ships had an alternative.

Of the 1,257 ships that entered Nieuwediep in 1855, 47 had a loaded draft of 5.9 m or more, and would still have had to partially unload, had the new lock been ready that year.

[35] The dimensions of Koopvaarders Lock III were: 65 m long, 17 m wide, and deep 6.71 m below high tide, or 6.50 m below AOD,[37] or 5.92 m below inland level.