Boat travel from PNG(Bougainvilla Island) to Solomon Islands

Hello.

How often are boats traveling from PNG south to Solomon Islands?
Approx cost? schedule? problems/pleasant surprises? immigration (passport stamping out of PNG and into SI)?
Timeframe for boat ... mid to late December

The only boats are locally owned outboards usually travellng to market. There is no schedule: they usually travel on market days. December is not the best time to try to travel in the area, as it is when all the locals are travelling home for holidays, and the usual things are in recess.
Search this branch for other posts on the subject, from people who have done the crossing.