Twelen is a 21.40-metre steel motor yacht, currently for sale through De Valk and viewable at their Monnickendam sales marina (link below), with one of the more interesting histories I’ve come across recently.
Built in 1979 at the Wisla shipyard in Gdansk, she began life as a sounding vessel for the German government. De Valk’s own listing states she’s been in private hands “for many years” since, and she’s currently on the market asking €149,500.
Personally, it is the first time I’ve come across a former European sounding vessel converted into a private cruiser which is one of the reasons why I wanted to feature her in this explorer yacht newsletter.
The yard that built her
Stocznia Wisla Gdansk isn’t a name that trips off the tongue like some of the more famous Polish yards, but the pedigree is there. The yard traces back to the rebuilding of Poland’s shipbuilding industry after the Second World War, became a state enterprise in 1950, and was folded into Poland’s Union of Sea Ship Repair Yards in 1967.
Over its history, it has built more than 1,500 vessels, many reportedly still working today, spanning specialised research, inspection, rescue, military, and passenger vessels.
Gdansk is better known internationally for the shipyard forever linked with the Solidarity movement, but Wisla built its own quieter reputation across that broad range of purpose-built working vessels. Twelen carries that pedigree in her steel.
What a sounding vessel actually does
I get asked some version of “what did she actually do” every time I feature an ex-working vessel, which is understandable.
Sounding vessels exist to measure water depth and map the seabed, a job that used to run through a simple echo-sounder and, on modern boats, increasingly means multibeam sonar. That data feeds nautical chart production, dredging surveys, cable and pipeline route planning and coastal engineering projects, work that keeps entire waterways navigable and safe for everyone else.
In practice, that would have had Twelen holding a steady course or sitting on station while onboard instruments took careful readings, nothing to do with speed and everything to do with being a stable, reliable, seaworthy and dependable platform.
That heritage explains a great deal about why she’s built the way she is.
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What her lines tell you
A length-to-beam ratio of roughly 4.5 to 1 is notably slender for a vessel her size and the kind of proportions naval architects associate with an easily driven displacement hull.
Her bow carries a moderate rake and a fine entry, with the sheerline lifting gently as it runs forward. That shape typically helps keep a bow dry in a head sea.
Aft of the wheelhouse, freeboard drops away, and the working deck runs low and long all the way to a near-vertical transom.
The wheelhouse itself sits forward of amidships, leaving most of her waterline length as clear, useable deck. That layout would have suited handling survey gear over the stern in her working life, and today suits tenders, diving kit or simply extra space under an awning.
Below the waterline, her hull curves smoothly from keel to waterline rather than breaking at a hard chine. That round-bilged shape tends to reduce wave-making resistance at displacement speeds and give a gentler motion through the water.
The usual trade-off with a round bilge is a greater tendency to roll in a beam sea, and her small bilge keels are the standard way of damping that roll without sacrificing the efficiency the hull shape offers. A rubbing strake runs the full length of her topsides at deck level. That is practical protection for a boat that spent decades working alongside quays and other craft.
The boat as she stands today
On paper, Twelen is 21.40 metres long with 4.81 metres of beam and a modest 1.50-metre draught, displacing 47 tonnes on a steel hull with an aluminium superstructure.
That shallow draught, combined with a mast that lowers electrically, points to a boat that can get into places a deeper, taller vessel can’t, and that matters for anyone weighing European canal cruising alongside coastal passages.
Power comes from twin Wola 53 ANM 59 H6AA diesels, 210hp apiece, driving through shafts to four-bladed fixed propellers, backed by a 25kVA Newage Stamford generator. Steering is hydraulic, with an inside helm position, and she was ashore in May 2025 for hull measurement, antifouling and hull painting, alongside fresh CVO certification.
Rockwool insulation and a Kabola KB45 central heating system, installed new in 2022, make her comfortable for a longer stay aboard.
For some buyers, she might be too ‘rugged looking’. But, for a buyer who understands the engineering that goes into these former commercial/worker vessels and who wants that engineering in their own explorer yacht platform, then the boat, along with her asking price, makes me think that she will not be on the market for long.
This article continues below in The Wardroom, the premium section of my newsletter. Thanks to my premium subscribers, I get to keep finding boats like Twelen and telling their stories.
In the premium section below, I cover:
- Why her fresh CVO certification matters for a private buyer
- The Wola engines, and the specialist businesses still supporting them today
- Her three-tank fuel capacity, and what it means for real endurance
- Where €149,500 sits against the wider market for steel-built vessels of a similar scale
- Who I think Twelen suits, and her liveaboard credentials as she stands today
- The sensible additions that would sharpen her for full-time life aboard
