Andrew,
Get yourself some car tyres.about ten will do. Borrow them from the local tyre place,and return them when you are finished.
Put two( double) behind the boat,for the stern to "land on".
You will have to adjust these, as you push your boat off the trailer,to get the landing spot correct.
Push the boat off,as you would normally launch.
The first two tyres become "the water"
Add more single tyres,( more water)under the keel as you drive your car forward,after the stern "has landed" A helper here is great.
If you can tie the stern to a tree,or post,that helps as you drive forward. Other wise you will need to assist by doing a little bit of pushing.
Deckie drives,you work.
As the boat comes off, say half way,Use tyres to support under both the sides of the boat, to stop her from tipping.
When reloading,leave the trailer off the car.
Slip the trailer into position,hook up the boat,and start winching.The trailer wiil work its way under the boat.Take care, as the trailer will lift off the ground,at the winch end.
I say take care , as you could end up with a dentist bill otherwise.
Take out the tyres as you go. Hook her back up to the car,and away you go.
You dont need luck, its an easy exercise,so long as you think of the tyres as the water. You cant drag the boat off the tyres, that is why you let the trailer work under the boat for retrieval.
David
Ps done it many times