Yeah.... but what if they were installed on Friday the 13th? Or perhaps in a leap year.... there's just too much to consider, overall. Since they're so close to the man's foot taking the picture, he should just take an air impact wrench and remove them. problem solved or maybe just buy another boat without keel bolts.Keelbolts need replacing every thirty years only if they were installed on Fridays. If they were installed on Mondays, you can wait thirty three years and one month. Tuesday installations last for thirty five years and six weeks. For Wednesdays add 15 months to Tuesdays. Thursday keelboat installations are only good for twelve years. Replacement also depends upon how the boat has been used (or misused). Boats that have been repeatedly run aground are likely to have more keelbolt issues. Boats that have had bilgewater sitting in them for long periods are more likely to have problems. especially if the bilgewater has been allowed to freeze repeatedly. The visible ends of the keelbolts - the threads and their nuts - do not necessarily indicate the condition of what's below the keelson and inside the keel itself, as noted above. If water has gotten into the keel/hull joint, or entered from the top through the bilge, who knows what sort of corrosion could have happened. Without pulling the bolts (not easy) there's no way to be sure. If the bolts look good and the keel doesnt' seem to be moving, there probably isnt much to worry about.