How to Inspect a Used Boat Before You Buy

Start with the hull. On fiberglass boats, look for osmotic blisters below the waterline — these appear as small to large bubbles in the gelcoat and indicate water penetration into the fiberglass laminate. Minor blistering is common on boats that have spent extensive time in the water and can be repaired, but extensive deep blistering is expensive to fix properly. Use a moisture meter on the hull — readings above 20% indicate elevated moisture in the fiberglass. Check the transom (the vertical rear panel where the motor mounts) by pressing firmly with your hands — a soft transom feels noticeably flexible and indicates rot in the wooden core. A soft transom is one of the most expensive boat repairs, often running $2,000–$8,000. Check the stringers (the longitudinal structural members running along the bottom of the hull) for the same softness. For aluminum boats, look for corrosion, cracks at stress points (especially at rivets and welds), and any prior repairs. Aluminum repairs are cheaper than fiberglass work but still a concern.

The motor is typically the most expensive component on a used boat. For outboard motors, check the hours on the digital gauge — under 300 hours is low, 300–800 is average, and over 1,000 hours means careful inspection is warranted. Ask for all service records. Flush the motor with fresh water if it's a saltwater or brackish-water boat. Check the impeller service history — water pump impellers should be replaced every 2–3 years and a failure causes catastrophic overheat damage. Sea trial the motor under actual operating conditions. It should start easily when cold, run smoothly at all RPM ranges including wide-open throttle, and reach its rated RPM range at full throttle (check the motor's operation manual for the spec). Smoking, rough idling, poor acceleration, or difficulty reaching rated RPM are red flags. After the sea trial, check under the engine cover for oil leaks and check the gear oil in the lower unit for a milky appearance (which indicates water intrusion past a failed seal).

A certified marine surveyor performs the professional equivalent of a home inspection for boats. The cost runs $15–$25 per foot of boat length — so about $300–$500 for a 20-foot boat. This is well worth it for any boat over $15,000 or any boat you plan to finance (lenders typically require a survey for loans over a certain amount). The surveyor checks everything in this guide plus areas that require specialized knowledge and equipment: hull integrity below the waterline, through-hull fittings, steering system, fuel system, bilge pumps, and safety equipment. The written survey report documents every finding with photos and gives you documentation to negotiate price reductions for any defects found.