Kaiteriteri

Go to detach from a trip ferry 3 hours so do not really want to travel too far in our destination.

As would be faster - Picton to Nelson 1 1 / 2 hours, then about an hour Nelson Kaiteriteri.
Another option is by bus or car to Koromiko - 10 minutes from Picton and take a small plane from there to Nelson with Sounds Air. I think they put on more flights recently. http://www.soundsair.com or http://www.openjet.com/static.jspapageNa ...

To be honest, when you pay for the ferry from Wellington to Picton and then on travel (through) Nelson is a lot cheaper to fly from Wellington to Nelson - generally you can get flights from 39 $. If you have not already booked to check this site every day - promotions are updated 2-3 times per day. http://www.grabaseat.co.nz

Edit - If you take a bus to Picton, you have to change over to Nelson Abel Tasman then take coaches (buses) to Abel Tasman NP.

Kia ora,
K Bear has the right idea, but if you need to take a bus, then google "K Bus (K Kaiteretere). They meet the ferry and take you directly to the Tasman Bay.

Rent a car from Picton. The scenery is magnificent. This way, you can drive around Queen Charlotte Sound. You could get a motel in Picton for the night and choose your rental car in the morning and be cool to get to Kaiteriteri. It would be a shame to get there by car feel a bit tired and not enjoy the beautiful landscape.