RE: Double fins?
Where I sail during Summer there is a large extension of shallow water with mud on the bottom, rocks and sea urchins. I use slalom materials and I am disadvantaged compared to my buddies on frrestyle boards and fins; others on bigger boards or Formula materials are in worse troubles than me.
Last Summer I met a guy using a two fin board with great satisfaction and this made me think. In the end, with such a board you have to buy two fins at a time; but I am not quite sure about real double expenditure, as a longer single fin will more often hit the bottm and get damaged.
In the end, a twin fin board could be a good solution in shallow waters; the real doubt is about performance. Theorically, a single fin with high A/R should be better; but I am not sure this is thoroughly confirmed in practice.