True, but the technique could (and still is) used today. Substitute the re-bar and add the supplements and you have a longer lasting concrete ship. Perhaps long enough to make it viable for a commercial vessel or a home hobbyist???
Maybe for my 49’ dream boat )(https://www.boatdesigns.com/49-Klondike-cruising-trawler-yacht/products/400/
or
https://hartley-boats.com/product/tahitian-fisherman-45-50/
A very rich friend of my parents (and to a degree me) had a huge yacht built for him out of concrete - built in Florida. He kept it on Lake Superior, and then after ten years or so he donated it to the University of Minnesota’s oceanography department.
I recall my dad telling me how he got to fly down to Florida for a few days with him on the private jet to go look at it during construction. Probably 1980 or so. Of course as a kid and hearing about a concrete boat I thought “that can’t be right!”