In 1994, I paid 11,000 euros for a 1974 Armagnac that was worth 3,000. The seller was charming, the woodwork smelled of polished teak, and I was 24 with a fresh naval engineering degree. Six months later, at the first haul-out, I saw what I hadn't known to look for: a hull pitted with osmosis across 70% of its surface, an 8-centimetre keel smile, and two cracked floors under the engine bay. The repair estimate exceeded the purchase price. I resold the boat at the same price to another naive young buyer, and from that experience I built an inspection checklist that has served me for the next three sailboats.
Key Facts
A professional osmosis treatment costs between 8,000 and 11,000 euros for a 12-metre hull, roughly 300 to 400 euros per square metre of underwater surface. Complete keel bolt replacement on a 10-metre cruising sailboat runs around 5,000 to 6,000 euros for labour alone, excluding transport and handling. An independent survey by a certified marine surveyor costs 1,000 to 1,500 euros for a 12-metre sailboat, with or without osmosis testing and sea trial. Rudder bearing replacement on a 10 to 11-metre sailboat comes in between 1,000 and 1,600 euros at a boatyard. Simple rule of thumb: if one or more of these points raises concern, the bill can represent 15 to 30% of the boat's purchase price.
Why a Checklist, Not an Exhaustive Guide
What I'm sharing here is my ten-point checklist. Ten points verified in this order, before even discussing price. If three are red flags, I don't commission a survey: I move on to another boat. If only one is problematic but quantifiable, I negotiate the repair cost, subject to an independent survey.
This checklist works for fibreglass cruising sailboats from the 1980s to 2015, which covers 80% of the used boat market in France. For aluminium boats, the logic is different and I won't cover it here.
Preliminary rule: I always do a first visit alone, without a surveyor, to screen. The certified surveyor (1,000 to 1,500 euros for a 12-metre boat) comes afterwards, on a boat I'm ready to buy. Never commission a survey before doing these ten checks yourself.
Point 1: Osmosis — the First Question I Ask
I always ask for the year of the last osmosis treatment and the corresponding invoice. No invoice means no treatment was done. On a boat over 20 years old that has never been treated, budget 8,000 to 11,000 euros for a 12-metre hull (specialist boatyards, Mediterranean and Atlantic, 2024-2026 prices). On smaller boats, expect 400 euros per square metre professionally, or 30 to 40 euros per square metre DIY with a good epoxy spray gun and six months ahead of you.
With the naked eye, at haul-out, I look for three things: micro-blisters of 2 to 8mm under the gelcoat, dark halos around through-hulls and the keel shoe, and residual moisture when I scrape with a utility knife at a discreet spot. Then the moisture meter: above 20% on a boat that's been out of the water for 3 months means active osmosis. Between 14 and 20% is a grey zone. Below 14%, you can breathe.
Point 2: The Keel — Weight That Wants to Fall Off
I check the keel-hull joint systematically. I'm looking for a visible gap, rust weeping from bolt heads, or hairline cracks in the filler around the joint. On an encapsulated keel (common on production boats from the 1980s-90s), I tap with a small hammer along the keel line to detect delamination.
Keel bolts are the most critical structural element on a ballasted sailboat. If they fail, you capsize. Replacement costs 5,000 to 6,000 euros minimum on a 10-metre boat, because it means lifting the keel off — which requires a crane, a cradle modification, and sometimes cutting access holes through the interior.
Point 3: The Rudder — Squeeze Test
I grab the trailing edge of the rudder and squeeze. On a healthy rudder, the skins don't flex. Any give means water has gotten in, the foam or wood core has degraded, and delamination is underway. A soggy rudder is a ticking time bomb.
I also lift the rudder vertically to check bearing play. More than 2mm of movement means the bearings need replacement (1,000 to 1,600 euros at a yard). On a skeg-hung rudder, I check the skeg attachment points for cracking.