Question: I have a type A,B,C extinguisher on the 34 foot sailboat( diesel engine). I am told I also need a type B2. Is this correct?

Answer: It's almost correct, this is what the rules state for your size boat:

Minimum number of extinguishers required:

Boat Length - No Fixed System - With Fixed System

26' to less than 40' - two B-1 or one B-2 - one B-1

So two B-1 extinguishers or one B2 would be acceptable unless you have a fixed system which you did not mention.