You need three barrels to build the base of the raft. However, after building the base (which contains three), one still remains. So two barrels are enough. Not only that, after building with two barrels and breaking the base, I have three barrels. In this way, the need to look for more disappears.
It is even convenient, but it spoils the immersion. This was the case in 0.74.00 and it is now (reinstall, no custom islands, no changes to settings).