You need to figure new sails/running and standing rigging/prop/lifelines/anchor rode and more on a 10 year lifespan (give or take). If your boat is painted you need to figure that too, periodically. Bottom paint? Engine maintenance? Hatch and canvas maintenance? Safety gear? A suit of high-tech sails is $10-15k for a 40-footer, and only good for about 7 or 8 years.

Add the insurance, yard bills, mooring/docks and you have to be near 10% of the boat's value.