On a trip to Jervis Bay in June 2000, a small group of around six relatively new and unexperienced members were launching the Daffodil from Summercloud Bay on the southern side of Jervis Bay. A bitumen road ends at Summercloud Bay, and the fairly steep beach mainly consists of fine soft sand. We launched the Daffodil without problems (we had a large and strong 4WD) and headed off to our dive. The weather was nice, with northerly winds and blue sky. After the dive, on our way back to Summercloud Bay, the weather had changed to quite strong southerly winds. Additionally the tide was rising. Arrived at Summercloud Bay, one of us jumped out to get the car, and the others were holding the Daffodil. One unexpected big wave, and already some water was in the boat. Strong winds, more waves and more water started to fill poor Daffi. Driving the trailer into the water, the car itself became stuck in soft sand, and while we were pushing the Daffodil onto the trailer - which was sinking into the sand - the car itself started to get bogged. Two more waves and the Daffodil was half flooded, including water in the console and battery compartment. Both trailer and car were bogged. Only with the help of another 4WD and after one rope had snapped we were able to first get the 4WD out of the soft sand, and then with a long rope (we made sure the car stayed on dry hard sand) we were able to first pull trailer out of the sand, and then the Daffodil separately. By then, water has flooded the battery bucket.
Lessons learned: We were an unexperienced group of new divers. One mistake was that we didn't really know how to launch and more important how to to retrieve a boat from a soft sandy beach. One way to do it safely is to attach a long strong rope to the bow (front) of the boat and pull it all the way up across the hard wet sand (i.e. further up than the current waves reach and to the edge of the dry sand). Then it is possible to drive the trailer onto the edge of the hard wet sand, and to winch the boat onto the trailer.
There are some hints on launching and retrievong over sand.