Virtually all cruising boat masts get rainwater into them, usually via the gaps near the sheaves at the masthead and any exit points for lines. Essentially impossible to avoid.
stepped masts usually have a drain hole at the base, and water
simply exits there. Some keel
stepped masts have some sort of dam at the deck
level, and an drain hole there that serves just as the deck stepped ones do. Often this dam is either missing or ineffectual, and thus water
reaches the below decks step. Sometimes (as on our boat) it is possible to drain this off to a lower bilge
or, in our case, the shower sump
. The amounts are usually small, and our shower sump
pump, on a float switch, empties it easily as would a proper bilge pump
. Nothing to worry about.
In the case of the OP's situation, it doesn't look like the foot of the mast
is seriously compromised; aluminium corrosion
products do make a disproportionate mess!. A good cleanup and inspection
would be in order, but I don't think it would indicate an immediate need for mitigation. The amount of corrosion
suggests that the spigot on the inside (the locating "pin") might be stainless, or that there is some scrap stainless lying about in there. If he should buy the boat, at a convenient time unstepping the mast
and checking everything out would be a good idea, but IMO, not a pressing matter.
No one likes water inside a boat, but at least this water is usually fresh, and delivered right to the bilge
area. How much nicer than deck leaks!