They use a very high pressure and high volume spray to wash off all the marine growth and it does a good job. The mussels littered the dry dock and didn't get cleaned up. That made for very dirty (and subsequently smelly) conditions for us and the workers and a field day for the flies that loved the rotting mussels and saturated mud. Other dry docks we have been in would have cleaned the dry dock down after pressure washing the boats. This one was full of discarded metal, anodes, general debris and thick oozing mud.
Our anodes are Magnesium by MG Duff and after 3 years of immersion, including 2 weeks in salt water, they appear to be pretty active. The picture above is of a small 2 Kg anode near the bow thruster tunnel, we have 8 of these and a further 8 x 4 Kg anodes on the length of the main hull. Various people, including our marine surveyor, suggest that aluminium anodes would be best for fresh water and Vankerkoven only carry zinc anodes. If you contact MG Duff or use their handy website guide it clearly shows that Magnesium is the right choice. The handy guide can be found at http://www.mgduff.co.uk/leisure-craft/hull-anode-selection/. We mention this because we see plenty of steel barges with anodes in good condition but with rusty hulls (including the commercial next to us in the dry dock which has pristine anodes), the anodes are clearly not doing their job.
This shows the underwater area which lost its bitumin coating within a week of our floating in 2008. We can only think that this was because the boat was refloated in salt water (to allow another ship to be dry docked) and not washed off again just before the bitumen was applied. You can see in the photo that the topsides still have their paint. What a waste of time and money it was putting it on the bottom.
The 2 anodes on the rudder have lost about a third of their weight but there is very little rust and plenty of anode left.
This is a gratuitous picture of Lorna and Tilly surveying the very busy Vankerkovens yard from across the canal during a morning walk. This is to compensate for all the descriptions of anodes and bargy stuff :-).