These boats are very low in the water. When they are rowed on tidal water which is sometimes rougher with good sized waves. You can get a kit consisting of boards at the bow (front) which stop water going over the side into the boat and a battery powered sump pump which will quickly pump any water in the boat out of the boat.
In this particular race on the Thames conditions were very bad. So bad that many boats sunk and the race was abandoned. From what I could see all the boats that sunk were ones without the rough water kit. And all the ones that did not sink had the kit fitted.
No comment from me.