SELECT COUNT("Year") FROM table_13607 WHERE "4th Day" = 'bumped wolfson'
How many years have a 4th Day of bumped wolfson?
CREATE TABLE table_13607 (
    "Year" real,
    "Finish position" text,
    "1st day" text,
    "2nd day" text,
    "3rd day" text,
    "4th Day" text
)