Can you connect 2 rafts in Ark?
No, but you can build on them.
Is there a height limit in raft?
While, as far as I know, there are no hardcoded limits to raft size, many people start to experience performance issues somewhere around 25×25 foundations in Survival Mode, give or take some depending to power of the computers running the game.
How many C4 does it take to destroy a Motorboat in Ark?
It takes only 7-8 direct rocket hits or 9 C4 to sink a motorboat.