A guest was hurt at my house. Does my policy cover it?
Generally yes, under personal liability, and that is exactly what it is for. The question is the limit, because a serious injury claim from a guest can exceed a standard homeowners liability limit comfortably. An umbrella above it is the inexpensive correction.
A friend crashed my boat. Whose insurance?
Normally yours, because cover follows the vessel, subject to the operator terms on your watercraft policy. Your limits and your record absorb it. It is worth checking who is permitted to operate before the weekend rather than after.
We entertain a lot. Should that change my limits?
It is a fair reason to raise them. More people at the property, more lending and more activity all increase both the chance and the likely size of a claim. Umbrella cover is cheap relative to a guest injury.