/\OK found the PBO article Oct 2009, “drying out on piles”. Here's a summary from people who do this a lot:
Step 1 Preparations
Survey the bottom. Concrete or gravel? Gravel/sand is better as it allows the keel to take up and minimize rocking movement. Try to avoid a sloped bottom as it can be tricky. Check out another boat doing it.
Check the tide tables, want to know how much time you will have and whether the next high tide will float you off. Here in the PNW tides are uneven.
Arrive early to allow time to set up
Know your tie-up strategy so the lines
are ready to go
Step 2 Coming alongside
Try to be alongside two pilings. If not you’ll need extra lines
to keep the boat from pivoting in a breeze.
It can help to have one of the pilings in line
with the mast, as it gives you a strong point for a breast line
that’s over the keel. Will need to watch the spreaders so the piling doesn't foul the rigging.
fore and aft against the piling or have two fenders
with a board across as a fender
Make sure you lines will slide up the pilings as the tide rises.
Have spring lines so the boat can’t slip forwards and backwards. The longer the better to help with the slope of the bottom
Step 3 Taking ground
As the water recedes keep an eye on the trim. Add extra springs if the boat is setting oddly. For example if she’s settling by the bow pressure on the bow spring will help control it.
Fenders may try to ride up as the tide drops be prepared to kick them down
Shifting weight fore and aft can help with unexpected movement.
Be prepared to adjust lines as you go down. They may snag in the piling. Once you touch bottom pull the breast lines in tight to compress the fenders and steady the boat.
Step 4 while dried out
Start with the keel and work up buys you extra time
Tide chart will tell you the time you have
Step 5 floating free
Keep an eye on the lines to make sure they’re not snagged and holding the boat down
As you float free you may need to burp the stern gland
Remember to undo the halyard before getting underway