Guide
Pre-Purchase Underwater Survey - What a Diver Can Tell You Before You Buy
Updated · By Daniel Garcia
A marine survey gives you the paperwork. An underwater inspection shows you what the hull actually looks like - often the more expensive set of problems.
What's Different from a Marine Survey
A certified marine surveyor is the right person for the overall condition assessment - they're looking at rigging, systems, engine, interior, paperwork, and giving you a formal report for insurance and financing.
An underwater inspection by a commercial diver is specifically about what's below the waterline. Survey reports often note 'hull condition unknown - not hauled' or 'hull condition below waterline requires verification.' An underwater diver inspection fills that gap without needing a haul-out.
What We Look At
A thorough pre-purchase underwater inspection covers:
- Hull surface - blistering, cracks, osmotic damage, impact marks, paint condition
- Keel attachment - visible keel bolts where accessible, keel-to-hull joint condition
- Rudder - post condition, bearing play, damage, attachment
- Prop and shaft - condition, pitting, dezincification, cutless bearing wear
- Shaft alignment (visual indicators like wear patterns)
- Through-hull fittings - corrosion, backing, visible condition
- Transducers and speed/depth/temp sensors
- Zincs - condition, placement, what's there vs what should be
- Antifouling paint condition - age indicators, adhesion, failure patterns
- Anything else unusual - previous repairs, modifications, signs of grounding
Red Flags That Should Change Your Offer or Walk You Away
Things we find occasionally that matter to a buyer:
- Significant hull blistering - not just cosmetic, could mean major paint or laminate work
- Keel joint concerns on sailboats - grinning, movement, visible gap
- Prop showing serious dezincification - replacement cost $500-$2000+
- Cutless bearing worn through - shaft wobble, requires haul to replace
- Rudder bearing play - haul-out level repair
- Through-hull corrosion - immediate replacement concern
- Evidence of grounding - scrapes, impact damage, previous repairs
- Depleted zincs that suggest long-term electrical issues
What We Can't Tell You
Honest about limits. An underwater visual inspection doesn't replace:
- A certified marine survey (we're not surveyors - insurers won't accept our report as a survey)
- Engine hours verification and mechanical assessment
- Moisture meter readings on the hull laminate - that's a surveyor's tool and typically done on the hard
- Ultrasonic thickness testing on metal hulls
- Inside-the-hull inspection - we see the outside
How the Process Works
Typical pre-purchase dive inspection in Victoria or the Gulf Islands:
- Buyer contacts us with the boat's location and timing. Often we're asked to work around a survey appointment.
- We dive the boat, typically 1-2 hours in the water depending on size and conditions.
- Full HD underwater video of everything listed above, plus still photos of anything notable.
- Written report within 48 hours summarising findings, with video and photo references.
- Phone call if we find anything significant - we call the buyer immediately rather than waiting for the report.
Common questions