At its most basic, a boat trailer is a wheeled frame designed to transport a boat across land by towing it behind a vehicle. The frame can be basic for small boats, but larger boats require more complex designs. The boat's weight, overall length, width, center of gravity, hull shape, engine(s), and many other factors determine the best boat trailer model. A sailboat, for example, requires a special boat trailer because of its deep keel and high winch stand.
New powerboats are often purchased with custom trailers made especially for the boat, right down to a matching paint scheme. The boat trailer might come with custom chrome wheels, electronic brakes that work in tandem with the vehicle's brakes, and other optional accessories.
A boat trailer can have a single, double or triple axle, depending on its rated weight capacity. While a small boat trailer sports a manual winch to haul the boat on to the trailer, larger models have one- or two-speed automatic winches. Most frames are made of a welded steel construction that features weatherproof paint. Lights and axles are fully submersible for launching.
The "bed" of the trailer consists of one or more sets of "bunks" or treated wood planks covered with durable indoor/outdoor material. The bunks are positioned lengthwise on either side of the trailer, slanted inward. The hull rests against these bunks. A boat trailer can have adjustable bunks, but most have stationary bunks. The shape of the hull determines the required positioning of the bunks.
The boat trailer connects to a car or truck via a locking "coupler" positioned at the end of the tow bar. The coupler slides down over the ball hitch on the vehicle. When the boat trailer is not in use, the coupler can be fitted with an optional flat lip coupler lock that will protect the boat trailer from theft by making it impossible to drop the coupler on to a ball hitch.
Before towing a boat, ensure that the winch and coupler are both locked and the boat has been secured. The electrical harness should be connected and all lights should be functioning properly. Routinely check tire pressure and tread wear. Some boat trailers provide a frame-mounted spare tire. For those that don't, this is a modification worth considering.