Stand at the stern and look forward along the topsides. You're checking for waves, ripples, pits, or other imperfections. Top-shelf fiberglass work is as smooth as a mirror. Also watch for flat spots on the sides and curves along the length of the chines that could mean the boat was removed from the mold before it cured. While you're at the stern, eyeball the rubrail. It should be straight with only minor hints of the silicone that's sealing it. Waviness indicates that the hull and deck didn't fit together cleanly.
SQUARE AND FAIR
If, in construction, the hull and deck don't line up, the hull can become twisted as the two parts are forced together. Even small differences can affect handling. To check, tape some string to the bow at the waterline and bring it back along one side of the boat to the edge of the transom. Do the same on the other side. The two lengths of string should be the same.
SEALED FOR LIFE
Traditionally, the best way to join the hull and deck is with bolts and then bonding from the inside with fiberglass. But technology marches on. Methacrylate adhesives, like Plexus, get the job done right also. The best places to look at how the joint was done are inside the anchor locker and engine compartment.
WOOD CAN BE GOOD
Wood stringers and frames have gotten a lot of bad press since the advent of fiberglass internal support structures. Wood can be acceptable if it's pressure treated to resist rot and encapsulated in fiberglass. Crawl into the engine room and look for at least 2" of overlapping glass cloth. You should see no "line bubbles," which look like white streaks, in the corners. Fiberglass structures must meet the hull evenly and be faired into the hull with putty. Any blobs of putty and lumps of built-up fiberglass is a sign of poor mating or bonding.
Position yourself on the other side of the boat from the salesperson before you try this trick. Put one hand palm down on the hull above the waterline and hit the hull about 3' away with your other fist. You shouldn't feel any vibration.
EARN YOUR STRIPES
Run your hand across the colors on the hullside. If the colors are all sprayed in the gel coat, you should feel no edges between them. This method provides the most durable finish. Painted-on graphics and vinyl decals have a raised edge and don't hold up, but they're easier to fix.
Take your thumb and stick it up a through-hull fitting. Now spread out the fingers of your hand. If you can stick your fingers into another through-hull fitting, they're too close together and could weaken the hull.
GO FOR THE BRONZE
Check out the materials the through-hulls are made of. Plastic is acceptable, but top-quality builders use bronze. When you're in the engine compartment, make sure the shutoff levers can be easily reached and the hoses are attached to the fittings with two stainless-steel clamps.
If you've ever had to raise your feet above your waist to climb a boarding ladder, you know how important it is to have several steps. A ladder should have a minimum of three steps with the lowest rung at least three feet below the water's surface. Best is a ladder that stows in its own locker to keep the swim platform clear.
Many boatbuilders say they include trim tabs as standard equipment on a boat, but the stock units are usually too small. Boats around 25' should have tabs at least 1'6" wide. Offshore go-fasts should have heavy-duty tabs such as Mercury K-Planes with dual hydraulic rams.