Most of the piracy off the W. African coast is centered around the delta
in Nigeria and now Benin. The only reported piracy even near where you are talking about is off Conakry, Guinea, not Senegal, and that stuff is happening to big ships close to shore. There is a good map at the IMB website showing reported pirate attacks for your reference: Live Piracy Report
Sailing in a convoy, or groups, only makes you a bigger target for the pirates. As a group you can only sail at the speed of the slowest member
which means you spend far longer in the pirate area than you would otherwise (unless you are the lucky slowest boat). Finally, what will you do when the boat next to you is attacked by drugged out crazies armed to the teeth with machine guns
and RPGs - throw tomatoes? No, there is nothing you can do but watch....and wait your turn because you will be next.
Having sailed through "Pirate Alley" by Somalia
a few years ago, I wouldn't even dream of it now. The best policy is avoidance, not the false sense of security
of sailing in a group of equally defenseless cruisers.