What to Know Before Buying a Used Boat: Finding Hull Issues

Almost without exception, when you buy a used boat, you’ll discover issues the first few times you run it that you missed before purchase — a float switch that sticks on, a bow light that doesn’t work, a leak in the livewell plumbing, a glitchy trim tab switch. It happens, and it’s not a big deal. In fact, you should assume going in that there will be a “punch list” phase, during which you find and fix assorted issues on your new-to-you boat.

On the other hand, discovering issues with the engine(s) and/or hull can be potentially catastrophic. Major engine repairs, rebuilds and replacements are expensive, as are structural repairs on fiberglass hulls. As a point of reference, MSRP on a new Yamaha F150 with mechanical controls is upwards of $15,500 in 2022. For an F250, it’s around $25,000. And significant hull repairs like replacing a transom or stringers can easily run well into five figures.

The point is that when evaluating a used boat, you should concentrate on the big stuff. A chartplotter that cuts out intermittently, a blown speaker, a torn leaning post cushion, aging trolling motor batteries — those are just opportunities for negotiation. It’s problems with the hull and/or the engine(s) that should make you think hard about walking away.

Fortunately, even with little or no mechanical know-how, you can perform a few simple checks that will tell you a lot about the condition of the engine(s) and hull. Let’s look at a few key indicators that can reveal issues with the hull itself. Remember, this is not an exhaustive checklist!

Universally, a transom that flexes excessively is bad news. It can be a sign that the transom itself is rotten, waterlogged, broken, and/or delaminated, or that the bonds between the transom and stringers and/or hull sides are failing. The easiest way to check for transom flex is to use the outboard engine. You can tilt the engine most of the way up and then “bump” the trim switch momentarily down a couple of times. On a bad transom, the engine will bounce up and down. Alternatively, you can use your hands on the anti-ventilation plate to “bounce” a tilted outboard, watching for flex in the transom.

On larger boats designed to hold big outboards, you can even trim the motor down, hug the cowling, stand on the anti-vent plate, and bounce or jump. You’ll definitely want to get the owner’s permission before jumping up and down on their engine though.

Aside from simply watching for flex, you can sometimes feel the flex in a transom by putting your fingertips along the joint between the hull and deck or along the bottom edge of the metal transom trim. When the outside face of the transom moves more or differently than the inside face, you can often feel the differential movement in your fingers. Cracking in the splash well is another good sign of transom flex.

Keep in mind that all transoms flex to some degree. A tilted outboard will always bounce up and down at least slightly. So how much is too much? That’s hard to quantify. But if you see enough flex to worry you — or if you see or feel differential movement where part or all of the transom moves independently of the rest of the boat — call in a surveyor or other professional to take a look.

Cracks in gelcoat are not at all uncommon on fiberglass boats. Whether they’re just cosmetic blemishes or indicate a serious problem has to do with where they are, how big they are, and how numerous they are.

The hull bottom is the most critical area to look for cracking. Minor longitudinal cracking along strakes and chines is relatively common, but longer cracks running bow to stern can indicate structural damage. If you see moisture weeping out — or evidence that it has in the past — you’re likely looking at something major.

Transverse cracking (oriented port to starboard) frequently indicates that stringers or bulkheads inside the hull are either failing or coming loose from the hull bottom, allowing the boat to flex front-to-back, also known as “oil canning.” Matching transverse cracks on both sides of the keel are a major red flag.

So-called “spider cracks” happen because gelcoat is less flexible and more brittle than fiberglass. When fiberglass flexes, its gelcoat “shell” develops minor cracks, especially along gunwales, around cleats and other deck hardware, and in corners. As a general rule, if you can’t fit your fingernail into a crack, it’s probably nothing to worry about.

In certain areas, though, cracking can suggest a larger problem. Cracks in the splash well, for example, can indicate transom issues, while cracking around T-top legs, deck plates, or other areas where fasteners penetrate the deck can result from water intrusion.

Star-shaped patterns of gelcoat cracks radiating out from a center point are caused by an impact. In many cases, they’re only cosmetic, but if it was a hard enough hit, it might also have damaged the fiberglass underneath.

Past structural repairs to a hull need not be a deal-breaker, but you should certainly know what you’re getting into. In some cases, the seller may not even be aware of repairs made before he or she owned the boat, so it’s ultimately up to you to look for the signs.

When not covered, hull repairs are usually revealed by areas of gelcoat with a slightly different color and/or texture. Sight along the hull sides and bottoms looking for texture variations. Look carefully at floors, paying particular attention to inconsistencies in nonskid texture or pattern and color. Hatches or deck plates that don’t match those on the rest of the boat are sometimes installed rather than refinishing an area that has been cut out for repair.

Again, a hull that has been repaired isn’t always a bad thing. In fact, a professionally repaired or rebuilt hull can be literally better than new. But there also are plenty of shady fiberglass repair people and businesses out there who either don’t know what they’re doing or cut corners to save money. The bottom line is that you need all the facts upfront.

The dreaded “soft spot” can be symptomatic of several issues: waterlogged foam coring; wet, swollen or rotten wood coring; or delamination of solid fiberglass laminate. All are cause for serious concern.

As boat building materials and methods have improved, large, obvious areas of deterioration have gotten less common. Instead, you’re looking for smaller areas of water intrusion in specific areas. Wet coring and delamination are typically found near where fasteners penetrate cored fiberglass, particularly around T-top and leaning post legs, deck and splashwell drains, hatches and inspection plates, and in areas where water collects and stands, like cockpit corners.

Fairly small areas of delamination and/or wet coring can often be repaired without great expense. They’re still red flags, though. If the way the boat was built (or the way it has been used or maintained) has allowed water intrusion in one spot, you can probably bet it will happen elsewhere too.

Unless you’re brand new to boating, you can generally feel it on the water when there’s something significantly wrong with a hull. Always, always sea trial a used boat and when you do, run the boat on plane through some chop — even across your own wake if that’s the only option. Boats with significant structural issues will shudder, flex, twist or even just sound wrong when they hit a wave.

Also, make sure that the boat can reach the engine manufacturer’s recommended wide-open throttle RPM range. An engine that won’t reach the recommended RPM range might simply be propped wrong, but it could also indicate the boat is carrying extra weight from wet coring or fiberglass.

At the dock, look closely at how the boat sits in the water with no people or heavy gear aboard. If it has scuppers, are they above the waterline? Does the boat list at all to port or starboard? Does it float “on its lines” — level front to back and side to side with the waterline parallel to any boot stripe or bottom paint? Floating stern low, floating low all around or list can indicate wet coring or glass.