Editor’s note: This is the first of a two-part series on inspecting a boat on its trailer.

Many buyers have the misconception that shopping for a trailerable boat (16 to 25 feet) is easier and involves a less-detailed inspection than when purchasing a larger vessel.

Although smaller boats typically have fewer complex systems to be concerned with, I’ve found that they are more likely to suffer from reliability issues, partially created by the lack of system redundancy (i.e., fuel filtration, battery charging). Also, because of their often low freeboard and low-cut transoms, smaller boats are much more prone to taking on water, even in a small chop.

When the right conditions exist, a bowrider can take water over the bow, flooding the cockpit. The same sea conditions might go mostly unnoticed with a 30-footer. I’m not implying that there is anything unsafe about trailerable boats — I own and enjoy a 21-foot center console — just that you need to pay close attention to certain areas.

When approaching the driveway purchase, a quick overview is in order. Consider the overall height, weight and beam of the boat and trailer package, as well as the roads you’ll have to travel to launch it. Be certain the boat/trailer package is within your tow vehicle’s rating and your capabilities as a driver. Ground clearance, even with the outboards or drives raised, can be an issue when backing into steep driveways.

If the boat has spent enough time in the water there will be a tide mark along the actual waterline, indicating whether the boat sits stern-heavy, possibly because of engines that are too heavy, or lists to either side. Inspect the hull from all sides, examining any through-hull fittings and their relationship to the waterline. Cockpit drains, bait well discharge fittings and scuppers should be as high above the boat’s waterline as practical. One or two people standing on the same side of the boat or at the stern can quickly place these fittings under water.

As a marine surveyor, among the first items I inspect are the cockpit drains. They typically direct water down to the through-hull fittings through inexpensive corrugated hoses that are notorious for splitting open. While under way or trailering, the weight of water in the hose, combined with the constant pounding of the boat, can cause the plastic through-hull fittings to fail at the hose connection. Then, any time the through-hull fitting dips below the water or deck water drains into the hose, the bilge fills, which can sink the vessel.

With a boat that’s stored on a trailer, it’s easy to inspect the hull and keel for structural and gelcoat damage. Look for scrapes from frozen trailer rollers and damage from intentional beaching or unintentional grounding. Bottom cracks, caused by pounding in seas, are found where strong structural components terminate. Pay particular attention to where chines and spray rails taper out, and where internal stringers, frames and bulkheads end. Observe the hull fairness and inspect for cracks where the boat rests on the trailer, especially where the rollers make contact. All sharp edges of the hull are vulnerable to chipping and air holes where the resin might not have run into the mold properly. The bow eye absorbs tension from the trailer winch while loading and road shock while trailering. It should be secure within the hull and have an oversized backing plate, which should be visible from inside the boat.

On outboard boats, the transom must be able to handle the weight of the engine both in the water and over the road. Inspect it carefully for stress cracks where it joins the hull sides, deck and bottom. Transoms can be real trouble spots on older boats, so take the time to properly assess what you’re looking at. Thorough sounding of the transom is recommended, as the bedding of outboard engine bolts deteriorates over time, allowing water to seep into the transom core. And excessive torque on engine mounting bolts can result in crushing the transom structure below the sacrificial doubling plates.

Although the boat you’re looking at lives on a trailer now, that doesn’t mean it always did. My center console hadn’t seen the water for more than five years when I purchased it on its trailer, though it became obvious that at some point it had spent considerable time in a slip or on a mooring. I hadn’t taken the time to sound the hull or remove a lower engine bolt until I got it home. As water trickled out of the mounting bolt hole, I realized my oversight. However, I was fortunate in that the boat was in line for a restoration anyway, so I simply added the transom repair to the to-do list. Lesson learned.

Next month, we’ll look at the engine, deck hardware, steering gear, the electrical system and more.

October 2012 issue