autoprop
can't talk to the 31, but we put an autoprop on our 356 and it's been fantastic! better performance and efficiency under power in forward and reverse, no prop walk, and a huge improvement in speed under sail. compared to the Hunter 3 blade fixed delivered on the boat we gained on the order of 3/4 kt with the autoprop under sail. well worth it! they can recommend the correct prop for your 31. BTW, their support and service have been excellent