Ernie,
The crane listed at Harbor Freight will lift a small boat, but may not be the slickest way. The hydraulic bottle jack (which has a 5" stroke) lifts the boom arm (which also telescopes manually) from horizontal to about 60 degrees or so.
If you are on salt water, you have to use a galvanized unit or it will be trashed in a few short years.
Even on fresh water, plan on giving it a real paint job before even installing it, since the orange Chinese stuff does not qualify as "paint" in any sense of the word.
I would suggest checking with boat and marine suppliers that sell various small cranes known as Davits that are intended for your purpose in galvanized and powder coated versions. Many are designed to mount directly to a dock pier so would also be easier to mount than the Harbor Freight model.
Good Luck,
Rip