SusCheck Blog · September 21, 2026 · Outboard boats

Red Flags When Buying a Used 16–24 ft Outboard Boat

A used outboard boat in the 16 to 24 foot range is the sweet spot of recreational boating — big enough for real water, small enough to trailer home. It’s also where the nastiest surprises in boating hide, because a boat’s worst problems are the ones you can’t see without knowing where to look.

The difference between a good buy and a bad one usually isn’t luck. It’s knowing which problems are structural, which are cosmetic, and which ones you can spot in the listing photos before you ever hook up the trailer.

Here are the red flags that matter, roughly in order of how serious they are.

1. Transom rot — the classic deal-breaker

The transom is the structural heart of an outboard boat. It carries the entire engine, and when the wood core inside it rots, the motor can literally tear itself off the back of the boat. This is the single most common reason a used outboard boat gets condemned.

In photos, look for:

• Stress cracks radiating from the motor-mount bolts — thin cracks spreading outward from where the engine bolts on are the transom flexing under load. Cosmetic gelcoat cracks in the corners are one thing; cracks anchored to the mount bolts are another.
• Discoloration or staining at the transom top edge and around through-transom fittings — water gets in through every bolt hole and fitting, and stains are its footprints.
• Sealant smeared around the bolts — somebody was chasing leaks through the transom core, which means there were leaks through the transom core.
• One new-looking section in an otherwise aged transom — a transom rebuild of unknown quality by an unknown person is not a selling point.

And ask the seller to do the wiggle test: grab the outboard and push and pull it firmly. Any flex, creaking, or movement in the transom is a walk-away until a marine surveyor says otherwise.

2. Waterlogged stringers and soft deck

The stringers are the boat’s skeleton — fiberglass-encased wood or foam running the length of the hull that everything else bolts to. When they rot or saturate, the hull loses its stiffness, and the repair means cutting the deck open.

In photos you can’t walk the deck, but you can look for the visual tells: deck gelcoat cracking in spiderweb patterns around cleats, rails, and the console base; rust streaks weeping from fasteners; visibly depressed or oil-canning deck sections; and soft, sagging, or water-stained floor panels. In bilge photos, look for standing water, heavy mold or mildew, stringers separated from the hull, or cracked tabbing where the stringers meet the hull sides.

Ask the seller to walk the deck and report any soft or spongy areas and exactly where they are. Soft spots don’t fix themselves, and they don’t stay small.

3. Hull damage — spider cracks vs. structural cracks

Not all cracks are equal. Learn the difference before you look at a single photo:

• Spider cracks (crazing) — fine surface cracks in the gelcoat, usually cosmetic, usually around stress points. Common on older boats. A watch item, not a deal-breaker.
• Structural cracks — deep cracks that show the fiberglass substrate underneath, cracks that flex when pressed, or large fractures from impact. These mean the laminate itself is damaged.

Also look for gouges through the gelcoat into the laminate, especially along the keel and chines; discolored or mismatched patches that signal prior fiberglass repair of unknown quality; chalky, oxidized gelcoat (cosmetic, but it tells you maintenance was neglected); and any visible hull deformation. Ask for the boat photographed out of the water so you can actually see the hull bottom — osmotic blistering down there needs a haul-out to assess properly.

4. Lower unit, skeg, and prop

The lower unit is the part of the engine that lives underwater and takes every hit. A bent, broken, or missing skeg means the boat hit something hard — and the question becomes what else got hit. Dinged, bent, or chewed-up propeller blades mean the same thing, plus vibration and lost performance.

Look for excessive paint bubbling on the lower unit, which is corrosion working underneath the paint, and heavy corrosion on the mounting bracket and tilt tube. Milky or emulsified oil at the drain plugs means water got into the gearcase — seals are shot. These are all visible in good close-up photos, and they’re all the kind of thing a seller hopes you won’t zoom in on.

5. Engine externals — what the cowling hides

Pop the cowling off in the photos (ask the seller to — if they won’t, that’s information too). What you want to see is a clean powerhead with intact wiring, pliable fuel lines, and no weeping. What you don’t want to see:

• Heavy corrosion on the powerhead or midsection — saltwater boats live hard, and corrosion doesn’t stop.
• Oil leaks or fuel weeping on or below the powerhead, or staining inside the cowling.
• Burnt, melted, or chafed wiring, cracked fuel lines, corroded hose clamps — the previous owner’s maintenance philosophy, in one photo.
• A seized or heavily corroded tilt/trim.

External condition doesn’t tell you compression or internal wear, but a neglected exterior almost never hides a pampered interior.

6. Electrical — corrosion and DIY wiring

Boat electrical systems live in a wet, vibrating environment, which is exactly the environment where bad wiring starts fires. In battery compartment and helm photos, look for corroded terminals, swollen or leaking batteries, and batteries that aren’t secured — a loose battery bouncing around the bilge is a short circuit waiting to happen.

The real tell is DIY wiring: wire nuts, electrical tape splices, and unfused add-on accessories are the marine equivalent of a “trust me” sticker. Green crust on connections, corroded fuse blocks, and dead navigation lights or pumps round out the picture. Ask the seller to test every switch and report what works. Tidy factory wiring with clean terminals is what you want to see.

7. The trailer — it strands more buyers than engines do

People inspect the boat and forget the trailer, then learn about it at 65 mph. Look at both sides of the frame, the tongue, and the crossmembers: surface rust is normal, but scaling or perforating rust — especially at welds and inside box tubing — is structural. Cracked welds, a bent tongue, or previous weld repairs deserve hard questions.

Check each wheel: bald, cracked, or mismatched tires, missing lug nuts, damaged bearing caps. Ask for the DOT date code on the trailer tires just like you would on the boat’s — trailer tires age out sitting in the driveway. Look at the winch strap for fraying, the winch itself for seizure or bends, bunks for worn-through carpet, and confirm the lights actually work. Non-functional brakes on a braked trailer are a safety issue, full stop.

8. Signs it sank

A boat that went down and came back up can look fine in glamour shots. Look for the evidence that stays: silt or waterlines high in the bilge and on interior surfaces, pervasive corrosion on every metal surface at the same level, heavy mold throughout compartments, and a musty or fuel smell the seller mentions a little too defensively. An engine that “just needs a tune-up” after “taking on some water” is a story, not a diagnosis.

If the boat was ever submerged, only a surveyor and a mechanic can tell you what’s actually salvageable. Photos can only tell you it happened.

9. The cover-up signs

Sometimes the red flag isn’t damage — it’s concealment. Be suspicious of:

• Fresh bottom paint over the whole hull (what’s it hiding — blisters? repairs?)
• Fresh sealant smeared around every fitting and bolt
• One suspiciously new transom, deck section, or upholstery panel in an otherwise original boat
• A listing with beautiful topside shots but no photos of the hull bottom, transom, bilge, or engine with the cowling off
• “Runs great” with no cold-start video offered and no sea trial allowed

A seller who photographs the HIN plate, opens every hatch, pulls the cowling, and shows you the boring stuff is usually a seller with nothing to hide.

10. What photos can’t tell you — the honest boundary

Here’s where a photo screen stops and the professionals start. Nobody can tell from pictures:

• Compression and internal engine condition — cylinder wear, crankshaft and bearing health, true engine hours. That takes a mechanic with a compression gauge.
• What’s inside the laminate — transom core and stringer core moisture need a surveyor with a moisture meter and a sounding hammer.
• Waterlogged foam — saturated flotation foam adds hundreds of pounds and hides rot, and it’s invisible from outside.
• Fuel tank internal corrosion — built-in aluminum tanks corrode from the inside out.
• Whether it actually runs right — only a cold start and a sea trial tell you if it planes, tracks straight, idles clean, and doesn’t overheat under load.

A photo pre-screen narrows the field. It doesn’t replace a marine surveyor, a mechanic, and a sea trial on the finalists.

11. Paperwork

Not visible in any photo: title status, lien history, theft records, and whether the HIN on the paperwork matches the HIN plate on the transom. Run the records check before money changes hands. A clean boat with a messy title is still a messy purchase.

What to ask the seller for

If the listing photos don’t cover the items above, ask for: the boat photographed out of the water with the hull bottom visible, the transom straight-on plus close-ups of the motor-mount bolts, the engine with the cowling off (powerhead from both sides), bilge photos with a flashlight, a close-up of the HIN plate and the hour meter, DOT date codes on the trailer tires, the wiggle-test result, and whether they’ll allow a cold start and a sea trial. A cooperative seller sends them within a day. An evasive one just told you something.

SusCheck is a photo pre-screen, not an inspection. Findings are based solely on what’s visible in the photos submitted. Always have the boat verified by a qualified marine surveyor and mechanic, including a sea trial, before purchase.