What can be done at the slip
Engine, fuel, fresh water and the head can all be winterized while the boat is still in the water. That's most of the job by time and by importance: oil changed, raw-water side protected with antifreeze or drained per the engine's own drain map, fuel stabilized, and the fresh water system, water heater and head flushed with non-toxic antifreeze. Doing this before haul-out means the work is done before the yard's own schedule gets backed up with everyone else's boats.
What has to wait until the boat is out
Sterndrive gear lube and anything below the waterline needs the boat out of the water, since you can't safely drain or inspect a drive or running gear while it's still submerged. That means the gear lube check, a look at the prop, anodes and any drive inspection happens once the boat is on the hard or on the trailer, as part of haul-out rather than the in-water winterizing visit.
Trailer boats are their own case
If your boat comes out of the water on a trailer at the end of every outing anyway, the entire winterizing job, engine, drive, fuel and fresh water, can be done in your driveway or storage lot in one visit, without the two-stage in-water/on-the-hard split that a slip-kept boat needs.
Shrink wrap and covers
A cover, whether shrink wrap or a fitted canvas cover, protects the boat from snow load and moisture, but it isn't a substitute for actually winterizing the systems underneath it. A well-covered boat with an unwinterized engine will still crack a block in a hard freeze; the cover keeps snow and rain out, it doesn't keep the water inside the engine from freezing. Plan the cover as the last step, after the mechanical winterizing is actually done, not instead of it.
A boat that sits at the slip late into the fall is still exposed to freezing water, not just freezing air. Don't assume a mild-looking week means it's safe to put off the raw-water side of winterizing.
Timing: book earlier than feels necessary
Haul-out season on Lake St. Clair generally runs from mid-October into early November, and the calendar for both haul-outs and winterizing visits tends to fill from the latest dates backward, meaning the owners who wait longest have the fewest options left. Booking as soon as you have a haul date, even if it's weeks out, is the simplest way to avoid being squeezed into the last, coldest slots on the schedule.
Booking with your dock neighbors
If a few boats on the same dock or the same row of a storage yard are all winterizing around the same time, it's worth coordinating so the same visit can cover all of them back to back. It's a small thing, but it tends to get everyone's boat handled sooner rather than each owner booking separately and waiting their turn.
Why the yard gets backed up
Marina and storage-yard haul-out schedules are built around the travel lift or trailer, not around winterizing itself, and every boat in the yard is competing for the same narrow fall window. A mechanic who can winterize the engine, fuel and fresh water systems at the slip before your boat's turn on the lift takes that part of the job off the yard's critical path entirely, so your haul-out slot only has to cover the parts that truly need the boat out of the water.
Boats on lifts, davits or racks
A boat kept on a lift, on davits, or already out of the water on a rack for the season skips the in-water stage altogether. In that case the whole job, engine, drive, fuel and fresh water, can usually be done in one visit, similar to a trailer boat, since nothing is submerged to begin with.
Related reading
For the actual mechanical steps, see how to winterize a sterndrive. For what to look at once the boat is out of the water, see the haul-out inspection checklist.
Get on the winterization list
Text the year, make and engine, or a photo of the engine, and your haul date.