Buyer due diligence · All · 12 min read
How to Read a Marine Survey Before You Buy a $250k+ Boat
Walk through valuation, moisture, engine hours, and deficiency language on a heavy fiberglass survey so you know what is negotiable before wire transfer.
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A/B/C findings and valuation bands
SAMS-trained surveyors often tag deficiencies by severity: A findings are cosmetic or routine maintenance (teak trim, canvas age), B findings need near-term spend (rudder bearing play, aged exhaust hoses), and C findings threaten seaworthiness or core structure (delaminated stringers, active moisture through balsa). On a $275,000 purchase, three C items totaling $32,000 should drive a price credit or exit—not a handshake repair promise.
The survey market value line is not decorative. If BUC/NADA suggests $268,000 retail but replacement cost is quoted at $310,000, your insurer may bind agreed hull value at $280,000 while the lender caps advance at 80% of $268,000 ($214,400)—a $21,600 gap versus 80% of ask.
Read whether the surveyor used market value, replacement cost, or forced-sale value. Brokerage listings above survey value need a written explanation (recent refit, new engines) backed by invoices—not ad copy.
Flag vague language like 'acceptable for intended use' without referencing ABYC or manufacturer specs; push for measurable standards tied to engine hours and compression notes.
Moisture, fasteners, and hull-deck joints
Phenolic hammer sounding along the hull-deck joint and transom should be uniform; hollow spots near cleats or chainplates often precede $8,000–$18,000 fastener remediation on 40-foot express cruisers.
Document Tramex or Sovereign moisture scale readings by location: dry fiberglass often reads under 12%, while readings above 22% in balsa or foam core panels justify core sample discussion and $4,000–$35,000 repair bands depending on area.
Photograph every through-hull inside and out; surveyors note age of valves and hoses—budget $1,200–$2,800 to replace below-water hoses discovered during haul-out on boats older than eight years.
If the survey references prior damage repair, demand yard invoices and re-scan those panels; patched impact zones on $250k+ boats can hide $15,000 tabbing rework.
Sea trial data that must match the report
Sea trial acceptance should log wide-open throttle RPM within 50 RPM of rating, time-to-plane seconds, and trim-tab response—if survey cites 4,200 RPM achieved but engines are rated to 4,400, that 200 RPM gap can mean prop pitch issues or engine health questions worth $5,000–$12,000 in diagnostics.
Record fuel burn at cruise (not just WOT): twin diesels burning 38 GPH at 28 knots versus a seller claim of 32 GPH is a $3,600 fuel delta over 100 hours annually at $6.00 per gallon.
Compare generator load test results under way—AC pulling 18 amps on both units while underway reveals alternator or belt issues separate from dockside checks.
Tie acceptance to survey: purchase agreements should say sea trial and survey must agree within stated engine-hour and moisture tolerances before deposit goes hard.
Sources
- SAMS — Survey standards — Society of Accredited Marine Surveyors
- NAMSGlobal — Surveyor finder — National Association of Marine Surveyors
Questions
Should I accept a survey paid for by the seller?
You can, but hire your own surveyor if scope, independence, or haul-out access looks limited—the $1,100–$1,800 re-survey cost beats a $20,000 missed moisture job.
How do BUC/NADA and survey value interact with my loan?
Lenders typically lend against the lower of contract price or survey market value; ask for the advance calculation in writing before you increase deposit.
What RPM spread triggers a renegotiation?
Many buyers renegotiate when WOT is more than 100 RPM below spec or when oil analysis shows metal counts outside lab limits—use your mechanic's thresholds in the acceptance clause.